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Updates:
Updated by:
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Keywords: TRILL, RBridge, IS-IS, reachability, overload, MTU, DEI, multicast, RPF, color, E-L1FS, purge
Internet Engineering Task Force (IETF) D. Eastlake 3rd
Request for Comments: 7780 M. Zhang
Obsoletes: 7180 Huawei
Updates: 6325, 7177, 7179 R. Perlman
Category: Standards Track EMC
ISSN: 2070-1721 A. Banerjee
Cisco
A. Ghanwani
Dell
S. Gupta
IP Infusion
February 2016
Transparent Interconnection of Lots of Links (TRILL):
Clarifications, Corrections, and Updates
Abstract
Since the publication of the TRILL (Transparent Interconnection of
Lots of Links) base protocol in 2011, active development and
deployment of TRILL have revealed errata in RFC 6325 and areas that
could use clarifications or updates. RFC 7177, RFC 7357, and an
intended replacement of RFC 6439 provide clarifications and updates
with respect to adjacency, the TRILL ESADI (End Station Address
Distribution Information) protocol, and Appointed Forwarders,
respectively. This document provides other known clarifications,
corrections, and updates. It obsoletes RFC 7180 (the previous "TRILL
clarifications, corrections, and updates" RFC), and it updates RFCs
6325, 7177, and 7179.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7780.
Eastlake, et al. Standards Track [Page 1]
RFC 7780 TRILL Clarifications, Corrections, Updates February 2016
Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Eastlake, et al. Standards Track [Page 2]
RFC 7780 TRILL Clarifications, Corrections, Updates February 2016
Table of Contents
1. Introduction (Changed) ..........................................5
1.1. Precedence (Changed) .......................................5
1.2. Changes That Are Not Backward Compatible (Unchanged) .......6
1.3. Terminology and Acronyms (Changed) .........................6
2. Overloaded and/or Unreachable RBridges (Unchanged) ..............7
2.1. Reachability ...............................................8
2.2. Distribution Trees .........................................8
2.3. Overloaded Receipt of TRILL Data Packets ...................9
2.3.1. Known Unicast Receipt ...............................9
2.3.2. Multi-Destination Receipt ...........................9
2.4. Overloaded Origination of TRILL Data Packets ...............9
2.4.1. Known Unicast Origination ..........................10
2.4.2. Multi-Destination Origination ......................10
2.4.2.1. An Example Network ........................10
2.4.2.2. Indicating OOMF Support ...................11
2.4.2.3. Using OOMF Service ........................11
3. Distribution Trees and RPF Check (Changed) .....................12
3.1. Number of Distribution Trees (Unchanged) ..................12
3.2. Distribution Tree Update Clarification (Unchanged) ........12
3.3. Multicast Pruning Based on IP Address (Unchanged) .........13
3.4. Numbering of Distribution Trees (Unchanged) ...............13
3.5. Link Cost Directionality (Unchanged) ......................13
3.6. Alternative RPF Check (New) ...............................14
3.6.1. Example of the Potential Problem ...................14
3.6.2. Solution and Discussion ............................15
4. Nickname Selection (Unchanged) .................................17
5. MTU (Maximum Transmission Unit) (Unchanged) ....................18
5.1. MTU-Related Errata in RFC 6325 ............................19
5.1.1. MTU PDU Addressing .................................19
5.1.2. MTU PDU Processing .................................20
5.1.3. MTU Testing ........................................20
5.2. Ethernet MTU Values .......................................20
6. TRILL Port Modes (Unchanged) ...................................21
7. The CFI/DEI Bit (Unchanged) ....................................22
8. Other IS-IS Considerations (Changed) ...........................23
8.1. E-L1FS Support (New) ......................................24
8.1.1. Backward Compatibility .............................24
8.1.2. E-L1FS Use for Existing (Sub-)TLVs .................25
8.2. Control Packet Priorities (New) ...........................26
8.3. Unknown PDUs (New) ........................................27
8.4. Nickname Flags APPsub-TLV (New) ...........................27
8.5. Graceful Restart (Unchanged) ..............................29
8.6. Purge Originator Identification (New) .....................29
9. Updates to RFC 7177 (Adjacency) (Changed) ......................30
Eastlake, et al. Standards Track [Page 3]
RFC 7780 TRILL Clarifications, Corrections, Updates February 2016
10. TRILL Header Update (New) .....................................31
10.1. Color Bit ................................................32
10.2. Flags Word Changes (Update to RFC 7179) ..................32
10.2.1. Extended Hop Count ................................32
10.2.1.1. Advertising Support ......................33
10.2.1.2. Ingress Behavior .........................33
10.2.1.3. Transit Behavior .........................33
10.2.1.4. Egress Behavior ..........................34
10.2.2. Extended Color Field ..............................34
10.3. Updated Flags Word Summary ...............................35
11. Appointed Forwarder Status Lost Counter (New) .................35
12. IANA Considerations (Changed) .................................37
12.1. Previously Completed IANA Actions (Unchanged) ............37
12.2. New IANA Actions (New) ...................................37
12.2.1. Reference Updated .................................37
12.2.2. The "E" Capability Bit ............................37
12.2.3. NickFlags APPsub-TLV Number and Registry ..........38
12.2.4. Updated TRILL Extended Header Flags ...............38
12.2.5. TRILL-VER Sub-TLV Capability Flags ................39
12.2.6. Example Nicknames .................................39
13. Security Considerations (Changed) .............................39
14. References ....................................................40
14.1. Normative References .....................................40
14.2. Informative References ...................................42
Appendix A. Life Cycle of a TRILL Switch Port (New) ...............45
Appendix B. Example TRILL PDUs (New) ..............................48
B.1. LAN Hello over Ethernet ...................................48
B.2. LSP over PPP ..............................................50
B.3. TRILL Data over Ethernet ..................................51
B.4. TRILL Data over PPP .......................................52
Appendix C. Changes to Previous RFCs (New) ........................53
C.1. Changes to Obsoleted RFC 7180 .............................53
C.1.1. Changes ..............................................53
C.1.2. Additions ............................................53
C.1.3. Deletions ............................................54
C.2. Changes to RFC 6325 .......................................55
C.3. Changes to RFC 7177 .......................................55
C.4. Changes to RFC 7179 .......................................55
Acknowledgments ...................................................56
Authors' Addresses ................................................56
Eastlake, et al. Standards Track [Page 4]
RFC 7780 TRILL Clarifications, Corrections, Updates February 2016
1. Introduction (Changed)
Since the TRILL base protocol [RFC6325] was published in 2011, active
development and deployment of TRILL have revealed errors in the
specification [RFC6325] and several areas that could use
clarifications or updates.
[RFC7177], [RFC7357], and [RFC6439bis] provide clarifications and
updates with respect to adjacency, the TRILL ESADI (End Station
Address Distribution Information) protocol, and Appointed Forwarders,
respectively. This document provides other known clarifications,
corrections, and updates to [RFC6325], [RFC7177], and [RFC7179].
This document obsoletes [RFC7180] (the previous TRILL
"clarifications, corrections, and updates" document), updates
[RFC6325], updates [RFC7177] as described in Section 9, and updates
[RFC7179] as described in Sections 10.2 and 10.3. The changes to
these RFCs are summarized in Appendix C.
Sections of this document are annotated as to whether they are "New"
technical material, material that has been technically "Changed", or
material that is technically "Unchanged", by the appearance of one of
these three words in parentheses at the end of the section header. A
section with only editorial changes is annotated as "(Unchanged)".
If no such notation appears, then the first notation encountered on
going to successively higher-level section headers (those with
shorter section numbers) applies. Appendix C describes changes,
summarizes material added, and lists material deleted.
1.1. Precedence (Changed)
In the event of any conflicts between this document and [RFC6325],
[RFC7177], or [RFC7179], this document takes precedence.
In addition, Section 1.2 of [RFC6325] ("Normative Content and
Precedence") is updated to provide a more complete precedence
ordering of the sections of [RFC6325], as shown below, where sections
to the left take precedence over sections to their right. There are
no known conflicts between these sections; however, Sections 1 and 2
are less detailed and do not mention every corner case, while
subsequent sections of [RFC6325] are more detailed. This precedence
is specified as a fallback in case some conflict is found in the
future.
4 > 3 > 7 > 5 > 2 > 6 > 1
Eastlake, et al. Standards Track [Page 5]
RFC 7780 TRILL Clarifications, Corrections, Updates February 2016
1.2. Changes That Are Not Backward Compatible (Unchanged)
The change made by Section 3.4 below (unchanged from Section 3.4 of
[RFC7180]) is not backward compatible with [RFC6325] but has
nevertheless been adopted to reduce distribution tree changes
resulting from topology changes.
Several other changes herein that are fixes to errata for [RFC6325]
-- [Err3002], [Err3003], [Err3004], [Err3052], [Err3053], and
[Err3508] -- may not be backward compatible with previous
implementations that conformed to errors in the specification.
1.3. Terminology and Acronyms (Changed)
This document uses the acronyms defined in [RFC6325], some of which
are repeated below for convenience, along with some additional
acronyms and terms, as follows:
BFD - Bidirectional Forwarding Detection.
Campus - A TRILL network consisting of TRILL switches, links, and
possibly bridges bounded by end stations and IP routers. For
TRILL, there is no "academic" implication in the name "campus".
CFI - Canonical Format Indicator [802].
CSNP - Complete Sequence Number PDU.
DEI - Drop Eligibility Indicator [802.1Q-2014].
FGL - Fine-Grained Labeling [RFC7172].
FS-LSP - Flooding Scope LSP.
OOMF - Overload Originated Multi-destination Frame.
P2P - Point-to-point.
PDU - Protocol Data Unit.
PSNP - Partial Sequence Number PDU.
RBridge - Routing Bridge, an alternative name for a TRILL switch.
RPFC - Reverse Path Forwarding Check.
SNPA - Subnetwork Point of Attachment (for example, Media Access
Control (MAC) address).
Eastlake, et al. Standards Track [Page 6]
RFC 7780 TRILL Clarifications, Corrections, Updates February 2016
ToS - Type of Service.
TRILL - Transparent Interconnection of Lots of Links or Tunneled
Routing in the Link Layer.
TRILL switch - A device implementing the TRILL protocol. An
alternative name for an RBridge.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
[RFC2119].
In this document, a "packet" usually refers to a TRILL Data packet or
TRILL IS-IS packet received from or sent to a TRILL switch, while a
"frame" usually refers to a native frame being received from or sent
to an end station. (The word "frame" also occurs in other contexts,
such as the "Frame Check Sequence" that is at the end of Ethernet
transmissions.)
2. Overloaded and/or Unreachable RBridges (Unchanged)
In this section, the term "neighbor" refers only to actual RBridges
and ignores pseudonodes.
RBridges may be in overload, as indicated by the [IS-IS] overload
flag in their LSPs (Link State PDUs). This means that either (1)
they are incapable of holding the entire link-state database and thus
do not have a view of the entire topology or (2) they have been
configured to have the overload bit set. Although networks should be
engineered to avoid actual link-state overload, it might occur under
various circumstances -- for example, if a very large campus included
one or more low-end TRILL switches.
It is a common operational practice to set the overload bit in an
[IS-IS] router (such as a TRILL switch) when performing maintenance
on that router that might affect its ability to correctly forward
packets; this will usually leave the router reachable for maintenance
traffic, but transit traffic will not be routed through it. (Also,
in some cases, TRILL provides for setting the overload bit in the
pseudonode of a link to stop TRILL Data traffic on an access link
(see Section 4.9.1 of [RFC6325]).)
[IS-IS] and TRILL make a reasonable effort to do what they can, even
if some TRILL switches/routers are in overload. They can do
reasonably well if a few scattered nodes are in overload. However,
actual least-cost paths are no longer assured if any TRILL switches
are in overload.
Eastlake, et al. Standards Track [Page 7]
RFC 7780 TRILL Clarifications, Corrections, Updates February 2016
For the effect of overload on the appointment of forwarders, see
[RFC6439bis].
2.1. Reachability
Packets are not least-cost routed through an overloaded TRILL switch,
although they may originate or terminate at an overloaded TRILL
switch. In addition, packets will not be least-cost routed over
links with cost 2**24 - 1 [RFC5305]; such links are reserved for
traffic-engineered packets, the handling of which is beyond the scope
of this document.
As a result, a portion of the campus may be unreachable for
least-cost routed TRILL Data because all paths to it would be either
through a link with cost 2**24 - 1 or through an overloaded RBridge.
For example, an RBridge (TRILL switch) RB1 is not reachable by TRILL
Data if all of its neighbors are connected to RB1 by links with cost
2**24 - 1. Such RBridges are called "data unreachable".
The link-state database at an RBridge -- for example, RB1 -- can also
contain information on TRILL switches that are unreachable by IS-IS
link-state flooding due to link or RBridge failures. When such
failures partition the campus, the TRILL switches adjacent to the
failure and on the same side of the failure as RB1 will update their
LSPs to show the lack of connectivity, and RB1 will receive those
updates. As a result, RB1 will be aware of the partition. Nodes on
the far side of the partition are both IS-IS unreachable and data
unreachable from RB1. However, LSPs held by RB1 for TRILL switches
on the far side of the failure will not be updated and may stay
around until they time out, which could be tens of minutes or longer.
(The default in [IS-IS] is twenty minutes.)
2.2. Distribution Trees
An RBridge in overload cannot be trusted to correctly calculate
distribution trees or correctly perform the RPFC (Reverse Path
Forwarding Check). Therefore, it cannot be trusted to forward
multi-destination TRILL Data packets. It can only appear as a leaf
node in a TRILL multi-destination distribution tree. Furthermore, if
all the immediate neighbors of an RBridge are overloaded, then it is
omitted from all trees in the campus and is unreachable by
multi-destination packets.
When an RBridge determines what nicknames to use as the roots of the
distribution trees it calculates, it MUST ignore all nicknames held
by TRILL switches that are in overload or are data unreachable. When
calculating RPFCs for multi-destination packets, an RBridge such as
RB1 MAY, to avoid calculating unnecessary RPFC state information,
Eastlake, et al. Standards Track [Page 8]
RFC 7780 TRILL Clarifications, Corrections, Updates February 2016
ignore any trees that cannot reach RB1, even if other RBridges list
those trees as trees that other TRILL switches might use. (However,
see Section 3.)
2.3. Overloaded Receipt of TRILL Data Packets
The receipt of TRILL Data packets by overloaded RBridge RB2 is
discussed in the subsections below. In all cases, the normal
Hop Count decrement is performed, and the TRILL Data packets are
discarded if the result is less than one or if the Egress Nickname is
illegal.
2.3.1. Known Unicast Receipt
RB2 will not usually receive unicast TRILL Data packets unless it is
the egress, in which case it egresses and delivers the data normally.
If RB2 receives a unicast TRILL Data packet for which it is not the
egress, perhaps because a neighbor does not yet know it is in
overload, RB2 MUST NOT discard the packet because the egress is an
unknown nickname, as it might not know about all nicknames due to its
overloaded condition. If any neighbor other than the neighbor from
which it received the packet is not overloaded, it MUST attempt to
forward the packet to one of those neighbors selected at random
[RFC4086]. If there is no such neighbor, the packet is discarded.
2.3.2. Multi-Destination Receipt
If RB2 in overload receives a multi-destination TRILL Data packet,
RB2 MUST NOT apply an RPFC because, due to overload, it might not do
so correctly. RB2 egresses and delivers the frame locally where it
is Appointed Forwarder for the frame's VLAN (or, if the packet is
FGL, for the VLAN that FGL maps to at the port), subject to any
multicast pruning. But because, as stated above, RB2 can only be the
leaf of a distribution tree, it MUST NOT forward a multi-destination
TRILL Data packet (except as an egressed native frame where RB2 is
Appointed Forwarder).
2.4. Overloaded Origination of TRILL Data Packets
Overloaded origination of unicast TRILL Data packets with known
egress and of multi-destination packets is discussed in the
subsections below.
Eastlake, et al. Standards Track [Page 9]
RFC 7780 TRILL Clarifications, Corrections, Updates February 2016
2.4.1. Known Unicast Origination
When RB2, an overloaded RBridge, ingresses or creates a known
destination unicast data packet, it delivers it locally if the
destination is local. Otherwise, RB2 unicasts it to any neighbor
TRILL switch that is not overloaded. It MAY use what routing
information it has to help select the neighbor.
2.4.2. Multi-Destination Origination
Overloaded RBridge RB2 ingressing or creating a multi-destination
data packet presents a more complex scenario than that of the known
unicast case, as discussed below.
2.4.2.1. An Example Network
For example, consider the network diagram below in which, for
simplicity, end stations and any bridges are not shown. There is one
distribution tree of which RB4 is the root, as represented by double
lines. Only RBridge RB2 is overloaded.
+-----+ +-----+ +-----+ +-----+
| RB7 +====+ RB5 +=====+ RB3 +=====+ RB1 |
+-----+ +--+--+ +-++--+ +--+--+
| || |
+---+---+ || |
+------+RB2(ov)|======++ |
| +-------+ || |
| || |
+--+--+ +-----+ ++==++=++ +--+--+
| RB8 +====+ RB6 +===++ RB4 ++=====+ RB9 |
+-----+ +-----+ ++=====++ +-----+
Since RB2 is overloaded, it does not know what the distribution tree
or trees are for the network. Thus, there is no way it can provide
normal TRILL Data service for multi-destination native frames. So,
RB2 tunnels the frame in a TRILL Data packet to a neighbor that is
not overloaded if it has such a neighbor that has signaled that it is
willing to offer this service. RBridges indicate this in their
Hellos as described below. This service is called the OOMF (Overload
Originated Multi-destination Frame) service.
- The multi-destination frame MUST NOT be locally distributed in
native form at RB2, because this would cause the frame to be
delivered twice. Instead, it is tunneling to a neighbor as
described in this section. For example, if RB2 locally distributed
a multicast native frame and then tunneled it to RB5, RB2 would get
a copy of the frame when RB3 transmitted it as a TRILL Data packet
Eastlake, et al. Standards Track [Page 10]
RFC 7780 TRILL Clarifications, Corrections, Updates February 2016
on the multi-access RB2-RB3-RB4 link. Since RB2 would, in general,
not be able to tell that this was a frame it had tunneled for
distribution, RB2 would decapsulate it and locally distribute it a
second time.
- On the other hand, if there is no neighbor of RB2 offering RB2 the
OOMF service, RB2 cannot tunnel the frame to a neighbor. In this
case, RB2 MUST locally distribute the frame where it is Appointed
Forwarder for the frame's VLAN and optionally subject to multicast
pruning.
2.4.2.2. Indicating OOMF Support
An RBridge RB3 indicates its willingness to offer the OOMF service to
RB2 in the TRILL Neighbor TLV in RB3's TRILL Hellos by setting a bit
associated with the SNPA (Subnetwork Point of Attachment, also known
as MAC address) of RB2 on the link (see the IANA Considerations
section). Overloaded RBridge RB2 can only distribute
multi-destination TRILL Data packets to the campus if a neighbor of
RB2 not in overload offers RB2 the OOMF service. If RB2 does not
have OOMF service available to it, RB2 can still receive
multi-destination packets from non-overloaded neighbors, and if RB2
should originate or ingress such a frame, it distributes it locally
in native form.
2.4.2.3. Using OOMF Service
If RB2 sees this OOMF (Overload Originated Multi-destination Frame)
service advertised for it by any of its neighbors on any link to
which RB2 connects, it selects one such neighbor by a means that is
beyond the scope of this document. Assuming that RB2 selects RB3 to
handle multi-destination packets it originates, RB2 MUST advertise in
its LSP that it might use any of the distribution trees that RB3
advertises so that the RPFC will work in the rest of the campus.
Thus, notwithstanding its overloaded state, RB2 MUST retain this
information from RB3 LSPs, which it will receive, as it is directly
connected to RB3.
RB2 then encapsulates such frames as TRILL Data packets to RB3 as
follows: "M" bit = 0; Hop Count = 2; Ingress Nickname = a nickname
held by RB2; and, since RB2 cannot tell what distribution tree RB3
will use, Egress Nickname = a special nickname indicating an OOMF
packet (see the IANA Considerations section). RB2 then unicasts this
TRILL Data packet to RB3. (Implementation of Item 4 in Section 4
below provides reasonable assurance that, notwithstanding its
overloaded state, the ingress nickname used by RB2 will be unique
within at least the portion of the campus that is IS-IS reachable
from RB2.)
Eastlake, et al. Standards Track [Page 11]
RFC 7780 TRILL Clarifications, Corrections, Updates February 2016
On receipt of such a packet, RB3 does the following:
- changes the Egress Nickname field to designate a distribution tree
that RB3 normally uses,
- sets the "M" bit to one,
- changes the Hop Count to the value it would normally use if it were
the ingress, and
- forwards the TRILL Data packet on that tree.
RB3 MAY rate-limit the number of packets for which it is providing
this service by discarding some such packets from RB2. The provision
of even limited bandwidth for OOMFs by RB3, perhaps via the slow
path, may be important to the bootstrapping of services at RB2 or at
end stations connected to RB2, such as supporting DHCP and ARP/ND
(Address Resolution Protocol / Neighbor Discovery). (Everyone
sometimes needs a little OOMF (pronounced "oomph") to get off the
ground.)
3. Distribution Trees and RPF Check (Changed)
Two corrections, a clarification, and two updates related to
distribution trees appear in the subsections below, along with an
alternative, stronger RPF (Reverse Path Forwarding) check. See also
Section 2.2.
3.1. Number of Distribution Trees (Unchanged)
In [RFC6325], Section 4.5.2, page 56, point 2, fourth paragraph, the
parenthetical "(up to the maximum of {j,k})" is incorrect [Err3052].
It should read "(up to k if j is zero or the minimum of (j, k) if j
is non-zero)".
3.2. Distribution Tree Update Clarification (Unchanged)
When a link-state database change causes a change in the distribution
tree(s), several possible types of change can occur. If a tree root
remains a tree root but the tree changes, then local forwarding and
RPFC entries for that tree should be updated as soon as practical.
Similarly, if a new nickname becomes a tree root, forwarding and RPFC
entries for the new tree should be installed as soon as practical.
However, if a nickname ceases to be a tree root and there is
sufficient room in local tables, the forwarding and RPFC entries for
the former tree MAY be retained so that any multi-destination TRILL
Data packets already in flight on that tree have a higher probability
of being delivered.
Eastlake, et al. Standards Track [Page 12]
RFC 7780 TRILL Clarifications, Corrections, Updates February 2016
3.3. Multicast Pruning Based on IP Address (Unchanged)
The TRILL base protocol specification [RFC6325] provides for, and
recommends the pruning of, multi-destination packet distribution
trees based on the location of IP multicast routers and listeners;
however, multicast listening is identified by derived MAC addresses
as communicated in the Group MAC Address sub-TLV [RFC7176].
TRILL switches MAY communicate multicast listeners and prune
distribution trees based on the actual IPv4 or IPv6 multicast
addresses involved. Additional Group Address sub-TLVs are provided
in [RFC7176] to carry this information. A TRILL switch that is only
capable of pruning based on derived MAC addresses SHOULD calculate
and use such derived MAC addresses from the multicast listener IPv4
or IPv6 address information it receives.
3.4. Numbering of Distribution Trees (Unchanged)
Section 4.5.1 of [RFC6325] specifies that, when building distribution
tree number j, node (RBridge) N that has multiple possible parents in
the tree is attached to possible parent number j mod p. Trees are
numbered starting with 1, but possible parents are numbered starting
with 0. As a result, if there are two trees and two possible
parents, then in tree 1 parent 1 will be selected, and in tree 2
parent 0 will be selected.
This is changed so that the selected parent MUST be (j-1) mod p. As
a result, in the case above, tree 1 will select parent 0, and tree 2
will select parent 1. This change is not backward compatible with
[RFC6325]. If all RBridges in a campus do not determine distribution
trees in the same way, then for most topologies, the RPFC will drop
many multi-destination packets before they have been properly
delivered.
3.5. Link Cost Directionality (Unchanged)
Distribution tree construction, like other least-cost aspects of
TRILL, works even if link costs are asymmetric, so the cost of the
hop from RB1 to RB2 is different from the cost of the hop from RB2 to
RB1. However, it is essential that all RBridges calculate the same
distribution trees, and thus all must use either the cost away from
the tree root or the cost towards the tree root. The text in
Section 4.5.1 of [RFC6325] is incorrect, as documented in [Err3508].
The text says:
In other words, the set of potential parents for N, for the tree
rooted at R, consists of those that give equally minimal cost
paths from N to R and ...
Eastlake, et al. Standards Track [Page 13]
RFC 7780 TRILL Clarifications, Corrections, Updates February 2016
but the text should say "from R to N":
In other words, the set of potential parents for N, for the tree
rooted at R, consists of those that give equally minimal cost
paths from R to N and ...
3.6. Alternative RPF Check (New)
[RFC6325] mandates a Reverse Path Forwarding (RPF) check on
multi-destination TRILL Data packets to avoid possible multiplication
and/or looping of multi-destination traffic during TRILL campus
topology transients. This check is logically performed at each TRILL
switch input port and determines whether it is arriving on the
expected port based on where the packet started (the ingress
nickname) and the tree on which it is being distributed. If not, the
packet is silently discarded. This check is fine for point-to-point
links; however, there are rare circumstances involving multi-access
("broadcast") links where a packet can be duplicated despite this
RPF check and other checks performed by TRILL.
Section 3.6.1 gives an example of the potential problem, and
Section 3.6.2 specifies a solution. This solution is an alternative,
stronger RPF check that TRILL switches can implement in place of the
RPF check discussed in [RFC6325].
3.6.1. Example of the Potential Problem
Consider this network:
F--A--B--C--o--D
|
E
All the links except the link between C, D, and E are point-to-point
links. C, D, and E are connected over a broadcast link represented
by the pseudonode "o". For example, they could be connected by a
bridged LAN. (Bridged LANs are transparent to TRILL.)
Although the choice of root is unimportant here, assume that D or F
is chosen as the root of a distribution tree so that it is obvious
that the tree looks just like the diagram above.
Eastlake, et al. Standards Track [Page 14]
RFC 7780 TRILL Clarifications, Corrections, Updates February 2016
Now assume that a link comes up from A to the same bridged LAN. The
network then looks like this:
+--------+
| |
F--A--B--C--o--D
|
E
Let's say the resulting tree in steady state includes all links
except the B-C link. After the network has converged, a packet that
starts from F will go F->A. Then A will send one copy on the A-B
link and another copy into the bridged LAN from which it will be
received by C and D.
Now consider a transition stage where A and D have acted on the new
LSPs and programmed their forwarding plane, while B and C have not
yet done so. This means that B and C both consider the link between
them to still be part of the tree. In this case, a packet that
starts out from F and reaches A will be copied by A into the A-B link
and to the bridged LAN. D's RPF check says to accept packets on this
tree coming from F over its port on the bridged LAN, so it gets
accepted. D is also adjacent to A on the tree, so the tree adjacency
check, a separate check mandated by [RFC6325], also passes.
However, the packet that gets to B gets sent out by B to C. C's RPF
check still has the old state, and it thinks the packet is OK. C
sends the packet along the old tree, which sends the packet into the
bridged LAN. D receives one more packet, but the tree adjacency
check passes at D because C is adjacent to D in the new tree as well.
The RPF check also passes at D because D's port on the bridged LAN is
OK for receiving packets from F.
So, during this transient state, D gets duplicates of every
multi-destination packet ingressed at F (unless the packet gets
pruned) until B and C act on the new LSPs and program their
forwarding tables.
3.6.2. Solution and Discussion
The problem stems from the RPF check described in [RFC6325] depending
only on the port at which a TRILL Data packet is received, the
ingress nickname, and the tree being used, that is, a check if
{ingress nickname, tree, input port} is a valid combination according
to the receiving TRILL switch's view of the campus topology. A
multi-access link actually has multiple adjacencies overlaid on one
physical link, and to avoid the problem shown in Section 3.6.1, a
stronger check is needed that includes the Layer 2 source address of
Eastlake, et al. Standards Track [Page 15]
RFC 7780 TRILL Clarifications, Corrections, Updates February 2016
the TRILL Data packet being received. (TRILL is a Layer 3 protocol,
and TRILL switches are true routers that logically strip the Layer 2
header from any arriving TRILL Data packets and add the appropriate
new Layer 2 header to any outgoing TRILL Data packet to get it to the
next TRILL switch, so the Layer 2 source address in a TRILL Data
packet identifies the immediately previous TRILL switch that
forwarded the packet.)
What is needed, instead of checking the validity of the triplet
{ingress nickname, tree, input port}, is to check that the quadruplet
{ingress nickname, source SNPA, tree, input port} is valid (where
"source SNPA" (Subnetwork Point of Attachment) is the Outer.MacSA for
an Ethernet link). Although it is true that [RFC6325] also requires
a check to ensure that a multi-destination TRILL Data packet is from
a TRILL switch that is adjacent in the distribution tree being used,
this check is separate from the RPF check, and these two independent
checks are not as powerful as the single unified check for a valid
quadruplet.
_______
/ \
RB1 ------ o ----- RB2
\_______/
However, this stronger RPF check is not without cost. In the simple
case of a multi-access link where each TRILL switch has only one port
on the link, it merely increases the size of validity entries by
adding the source SNPA (Outer.MacSA). However, assume that some
TRILL switch RB1 has multiple ports attached to a multi-access link.
In the figure above, RB1 is shown with three ports on the
multi-access link. RB1 is permitted to load split multi-destination
traffic it is sending into the multi-access link across those ports
(Section 4.4.4 of [RFC6325]). Assume that RB2 is another TRILL
switch on the link and RB2 is adjacent to RB1 in the distribution
tree. The number of validity quadruplets at RB2 for ingress
nicknames whose multi-destination traffic would arrive through RB1 is
multiplied by the number of ports RB1 has on the access link, because
RB2 has to accept such traffic from any such ports. Although such
instances seem to be very rare in practice, the number of ports an
RBridge has on a link could in principle be tens or even a hundred or
more ports, vastly increasing the RPF check state at RB2 when this
stronger RPF check is used.
Another potential cost of the stronger RPF check is increased
transient loss of multi-destination TRILL Data packets during a
topology change. For TRILL switch D, the new stronger RPF check is
(tree->A, Outer.MacSA=A, ingress=A, arrival port=if1), while the old
one was (tree->A, Outer.MacSA=C, ingress=A, arrival port=if1).
Eastlake, et al. Standards Track [Page 16]
RFC 7780 TRILL Clarifications, Corrections, Updates February 2016
Suppose that both A and B have switched to the new tree for multicast
forwarding but D has not updated its RPF check yet; the multicast
packet will then be dropped at D's input port, because D still
expects a packet from "Outer.MacSA=C". But we do not have this
packet loss issue if the weaker triplet check (tree->A, ingress=A,
arrival port=if1) is used. Thus, the stronger check can increase the
RPF check discard of multi-destination packets during topology
transients.
Because of these potential costs, implementation of this stronger
RPF check is optional. The TRILL base protocol is updated to provide
that TRILL switches MUST, for multi-destination packets, either
implement the RPF and other checks as described in [RFC6325] or
implement this stronger RPF check as a substitute for the [RFC6325]
RPF and tree adjacency checks. There is no problem with a campus
having a mixture of TRILL switches, some of which implement one of
these RPF checks and some of which implement the other.
4. Nickname Selection (Unchanged)
Nickname selection is covered by Section 3.7.3 of [RFC6325].
However, the following should be noted:
1. The second sentence in the second bullet item in Section 3.7.3 of
[RFC6325] on page 25 is erroneous [Err3002] and is corrected as
follows:
o The occurrence of "IS-IS ID (LAN ID)" is replaced with
"priority".
o The occurrence of "IS-IS System ID" is replaced with "7-byte
IS-IS ID (LAN ID)".
The resulting corrected sentence in [RFC6325] reads as follows:
If RB1 chooses nickname x, and RB1 discovers, through receipt
of an LSP for RB2 at any later time, that RB2 has also chosen
x, then the RBridge or pseudonode with the numerically higher
priority keeps the nickname, or if there is a tie in priority,
the RBridge with the numerically higher 7-byte IS-IS ID
(LAN ID) keeps the nickname, and the other RBridge MUST select
a new nickname.
2. In examining the link-state database for nickname conflicts,
nicknames held by IS-IS unreachable TRILL switches MUST be
ignored, but nicknames held by IS-IS reachable TRILL switches
MUST NOT be ignored even if they are data unreachable.
Eastlake, et al. Standards Track [Page 17]
RFC 7780 TRILL Clarifications, Corrections, Updates February 2016
3. An RBridge may need to select a new nickname, either initially
because it has none or because of a conflict. When doing so, the
RBridge MUST consider as available all nicknames that do not
appear in its link-state database or that appear to be held by
IS-IS unreachable TRILL switches; however, it SHOULD give
preference to selecting new nicknames that do not appear to be
held by any TRILL switch in the campus, reachable or unreachable,
so as to minimize conflicts if IS-IS unreachable TRILL switches
later become reachable.
4. An RBridge, even after it has acquired a nickname for which there
appears to be no conflicting claimant, MUST continue to monitor
for conflicts with the nickname or nicknames it holds. It does so
by monitoring any received LSPs that should update its link-state
database for any occurrence of any of its nicknames held with
higher priority by some other TRILL switch that is IS-IS reachable
from it. If it finds such a conflict, it MUST select a new
nickname, even when in overloaded state. (It is possible to
receive an LSP that should update the link-state database but does
not do so due to overload.)
5. In the very unlikely case that an RBridge is unable to obtain a
nickname because all valid RBridge nicknames (0x0001 through
0xFFBF inclusive) are in use with higher priority by IS-IS
reachable TRILL switches, it will be unable to act as an ingress,
egress, or tree root but will still be able to function as a
transit TRILL switch. Although it cannot be a tree root, such an
RBridge is included in distribution trees computed for the campus
unless all its neighbors are overloaded. It would not be possible
to send a unicast RBridge Channel message specifically to such a
TRILL switch [RFC7178]; however, it will receive unicast RBridge
Channel messages sent by a neighbor to the Any-RBridge egress
nickname and will receive appropriate multi-destination RBridge
Channel messages.
5. MTU (Maximum Transmission Unit) (Unchanged)
MTU values in TRILL are derived from the originatingL1LSPBufferSize
value communicated in the IS-IS originatingLSPBufferSize TLV [IS-IS].
The campus-wide value Sz, as described in Section 4.3.1 of [RFC6325],
is the minimum value of originatingL1LSPBufferSize for the RBridges
in a campus, but not less than 1470. The MTU testing mechanism and
limiting LSPs to Sz assure that the LSPs can be flooded by IS-IS and
thus that IS-IS can operate properly.
Eastlake, et al. Standards Track [Page 18]
RFC 7780 TRILL Clarifications, Corrections, Updates February 2016
If an RBridge knows nothing about the MTU of the links or the
originatingL1LSPBufferSize of other RBridges in a campus, the
originatingL1LSPBufferSize for that RBridge should default to the
minimum of the LSP size that its TRILL IS-IS software can handle and
the minimum MTU of the ports that it might use to receive or transmit
LSPs. If an RBridge does have knowledge of link MTUs or other
RBridge originatingL1LSPBufferSize, then, to avoid the necessity of
regenerating the local LSPs using a different maximum size, the
RBridge's originatingL1LSPBufferSize SHOULD be configured to the
minimum of (1) the smallest value that other RBridges are, or will
be, announcing as their originatingL1LSPBufferSize and (2) a value
small enough that the campus will not partition due to a significant
number of links with limited MTUs. However, as specified in
[RFC6325], in no case can originatingL1LSPBufferSize be less than
1470. In a well-configured campus, to minimize any LSP regeneration
due to resizing, all RBridges will be configured with the same
originatingL1LSPBufferSize.
Section 5.1 below corrects errata in [RFC6325], and Section 5.2
clarifies the meaning of various MTU limits for TRILL Ethernet links.
5.1. MTU-Related Errata in RFC 6325
Three MTU-related errata in [RFC6325] are corrected in the
subsections below.
5.1.1. MTU PDU Addressing
Section 4.3.2 of [RFC6325] incorrectly states that multi-destination
MTU-probe and MTU-ack TRILL IS-IS PDUs are sent on Ethernet links
with the All-RBridges multicast address as the Outer.MacDA [Err3004].
As TRILL IS-IS PDUs, when multicast on an Ethernet link, these
multi-destination MTU-probe and MTU-ack PDUs MUST be sent to the
All-IS-IS-RBridges multicast address.
Eastlake, et al. Standards Track [Page 19]
RFC 7780 TRILL Clarifications, Corrections, Updates February 2016
5.1.2. MTU PDU Processing
As discussed in [RFC6325] and (in more detail) [RFC7177], MTU-probe
and MTU-ack PDUs MAY be unicast; however, Section 4.6 of [RFC6325]
erroneously does not allow for this possibility [Err3003]. It is
corrected by replacing Item 1 in Section 4.6.2 of [RFC6325] with the
following text, to which TRILL switches MUST conform:
1. If the Ethertype is L2-IS-IS and the Outer.MacDA is either
All-IS-IS-RBridges or the unicast MAC address of the receiving
RBridge port, the frame is handled as described in
Section 4.6.2.1.
The reference to "Section 4.6.2.1" in the above text is to that
section in [RFC6325].
5.1.3. MTU Testing
The last two sentences of Section 4.3.2 of [RFC6325] contain errors
[Err3053]. They currently read as follows:
If X is not greater than Sz, then RB1 sets the "failed minimum MTU
test" flag for RB2 in RB1's Hello. If size X succeeds, and X >
Sz, then RB1 advertises the largest tested X for each adjacency in
the TRILL Hellos RB1 sends on that link, and RB1 MAY advertise X
as an attribute of the link to RB2 in RB1's LSP.
They should read as follows:
If X is not greater than or equal to Sz, then RB1 sets the "failed
minimum MTU test" flag for RB2 in RB1's Hello. If size X
succeeds, and X >= Sz, then RB1 advertises the largest tested X
for each adjacency in the TRILL Hellos RB1 sends on that link,
and RB1 MAY advertise X as an attribute of the link to RB2 in
RB1's LSP.
5.2. Ethernet MTU Values
originatingL1LSPBufferSize is the maximum permitted size of LSPs
starting with and including the IS-IS 0x83 "Intradomain Routeing
Protocol Discriminator" byte. In Layer 3 IS-IS,
originatingL1LSPBufferSize defaults to 1492 bytes. (This is because,
in its previous life as DECnet Phase V, IS-IS was encoded using the
SNAP SAP (Subnetwork Access Protocol Service Access Point) [RFC7042]
format, which takes 8 bytes of overhead and 1492 + 8 = 1500, the
classic Ethernet maximum. When standardized by ISO/IEC [IS-IS] to
use Logical Link Control (LLC) encoding, this default could have been
increased by a few bytes but was not.)
Eastlake, et al. Standards Track [Page 20]
RFC 7780 TRILL Clarifications, Corrections, Updates February 2016
In TRILL, originatingL1LSPBufferSize defaults to 1470 bytes. This
allows 27 bytes of headroom or safety margin to accommodate legacy
devices with the classic Ethernet maximum MTU, despite headers such
as an Outer.VLAN.
Assuming that the campus-wide minimum link MTU is Sz, RBridges on
Ethernet links MUST limit most TRILL IS-IS PDUs so that PDUz (the
length of the PDU starting just after the L2-IS-IS Ethertype and
ending just before the Ethernet Frame Check Sequence (FCS)) does not
exceed Sz. The PDU exceptions are TRILL Hello PDUs, which MUST NOT
exceed 1470 bytes, and MTU-probe and MTU-ack PDUs that are padded by
an amount that depends on the size being tested (which may
exceed Sz).
Sz does not limit TRILL Data packets. They are only limited by the
MTU of the devices and links that they actually pass through;
however, links that can accommodate IS-IS PDUs up to Sz would
accommodate, with a generous safety margin, TRILL Data packet
payloads of (Sz - 24) bytes, starting after the Inner.VLAN and ending
just before the FCS.
Most modern Ethernet equipment has ample headroom for frames with
extensive headers and is sometimes engineered to accommodate 9 KB
jumbo frames.
6. TRILL Port Modes (Unchanged)
Section 4.9.1 of [RFC6325] specifies four mode bits for RBridge ports
but may not be completely clear on the effects of all combinations of
bits in terms of allowed frame types.
Eastlake, et al. Standards Track [Page 21]
RFC 7780 TRILL Clarifications, Corrections, Updates February 2016
The table below explicitly indicates the effects of all possible
combinations of the TRILL port mode bits. "*" in one of the first
four columns indicates that the bit can be either zero or one. The
remaining columns indicate allowed frame types. The "disable bit"
normally disables all frames; however, as an implementation choice,
some or all low-level Layer 2 control messages can still be sent or
received. Examples of Layer 2 control messages are those control
frames for Ethernet identified in Section 1.4 of [RFC6325] or PPP
link negotiation messages [RFC6361].
+-+-+-+-+--------+-------+-------+-------+-------+
|D| | | | | | | | |
|i| |A| | | | TRILL | | |
|s| |c|T| |Native | Data | | |
|a| |c|r| |Ingress| | | |
|b|P|e|u| | | LSP | | |
|l|2|s|n|Layer 2 |Native | SNP | TRILL | P2P |
|e|P|s|k|Control |Egress | MTU | Hello | Hello |
+-+-+-+-+--------+-------+-------+-------+-------+
|0|0|0|0| Yes | Yes | Yes | Yes | No |
+-+-+-+-+--------+-------+-------+-------+-------+
|0|0|0|1| Yes | No | Yes | Yes | No |
+-+-+-+-+--------+-------+-------+-------+-------+
|0|0|1|0| Yes | Yes | No | Yes | No |
+-+-+-+-+--------+-------+-------+-------+-------+
|0|0|1|1| Yes | No | No | Yes | No |
+-+-+-+-+--------+-------+-------+-------+-------+
|0|1|0|*| Yes | No | Yes | No | Yes |
+-+-+-+-+--------+-------+-------+-------+-------+
|0|1|1|*| Yes | No | No | No | Yes |
+-+-+-+-+--------+-------+-------+-------+-------+
|1|*|*|*|Optional| No | No | No | No |
+-+-+-+-+--------+-------+-------+-------+-------+
The formal name of the "access bit" above is the "TRILL traffic
disable bit". The formal name of the "trunk bit" is the "end-station
service disable bit" [RFC6325].
7. The CFI/DEI Bit (Unchanged)
In May 2011, the IEEE promulgated IEEE Std 802.1Q-2011, which changed
the meaning of the bit between the priority and VLAN ID bits in the
payload of C-VLAN tags. Previously, this bit was called the CFI
(Canonical Format Indicator) bit [802] and had a special meaning in
connection with IEEE 802.5 (Token Ring) frames. After 802.1Q-2011
and in subsequent versions of 802.1Q -- the most current of which is
Eastlake, et al. Standards Track [Page 22]
RFC 7780 TRILL Clarifications, Corrections, Updates February 2016
[802.1Q-2014] -- this bit is now the DEI (Drop Eligibility Indicator)
bit. (The corresponding bit in S-VLAN/B-VLAN tags has always been a
DEI bit.)
The TRILL base protocol specification [RFC6325] assumed, in effect,
that the link by which end stations are connected to TRILL switches
and the restricted virtual link provided by the TRILL Data packet are
IEEE 802.3 Ethernet links on which the CFI bit is always zero.
Should an end station be attached by some other type of link, such as
a Token Ring link, [RFC6325] implicitly assumed that such frames
would be canonicalized to 802.3 frames before being ingressed, and
similarly, on egress, such frames would be converted from 802.3 to
the appropriate frame type for the link. Thus, [RFC6325] required
that the CFI bit in the Inner.VLAN, which is shown as the "C" bit in
Section 4.1.1 of [RFC6325], always be zero.
However, for TRILL switches with ports conforming to the change
incorporated in the IEEE 802.1Q-2011 standard, the bit in the
Inner.VLAN, now a DEI bit, MUST be set to the DEI value provided by
the port interface on ingressing a native frame. Similarly, this bit
MUST be provided to the port when transiting or egressing a TRILL
Data packet. As with the 3-bit Priority field, the DEI bit to use in
forwarding a transit packet MUST be taken from the Inner.VLAN. The
exact effect on the Outer.VLAN DEI and priority bits, and whether or
not an Outer.VLAN appears at all on the wire for output frames, may
depend on output port configuration.
TRILL campuses with a mixture of ports, some compliant with versions
of 802.1Q from IEEE Std 802.1Q-2011 onward and some compliant with
pre-802.1Q-2011 standards, especially if they have actual Token Ring
links, may operate incorrectly and may corrupt data, just as a
bridged LAN with such mixed ports and links would.
8. Other IS-IS Considerations (Changed)
This section covers Extended Level 1 Flooding Scope (E-L1FS) support,
control packet priorities, unknown PDUs, the Nickname Flags
APPsub-TLV, graceful restart, and the Purge Originator
Identification TLV.
Eastlake, et al. Standards Track [Page 23]
RFC 7780 TRILL Clarifications, Corrections, Updates February 2016
8.1. E-L1FS Support (New)
TRILL switches MUST support E-L1FS PDUs [RFC7356] and MUST include a
Scope Flooding Support TLV [RFC7356] in all TRILL Hellos they send
indicating support for this scope and any other FS-LSP scopes that
they support. This support increases the number of fragments
available for link-state information by over two orders of magnitude.
(See Section 9 for further information on support of the Scope
Flooding Support TLV.)
In addition, TRILL switches MUST advertise their support of E-L1FS
flooding in a TRILL-VER sub-TLV Capability Flag (see [RFC7176] and
Section 12.2). This flag is used by a TRILL switch, say RB1, to
determine support for E-L1FS by some remote RBx. The alternative of
simply looking for an E-L1FS FS-LSP originated by RBx fails because
(1) RBx might support E-L1FS flooding but is not originating any
E-L1FS FS-LSPs and (2) even if RBx is originating E-L1FS FS-LSPs
there might, due to legacy TRILL switches in the campus, be no path
between RBx and RB1 through TRILL switches supporting E-L1FS
flooding. If that were the case, no E-L1FS FS-LSP originated by RBx
could get to RB1.
E-L1FS will commonly be used to flood TRILL GENINFO TLVs and enclosed
TRILL APPsub-TLVs [RFC7357]. For robustness, E-L1FS fragment zero
MUST NOT exceed 1470 bytes in length; however, if such a fragment is
received that is larger, it is processed normally. It is anticipated
that in the future some particularly important TRILL APPsub-TLVs will
be specified as being flooded in E-L1FS fragment zero. TRILL GENINFO
TLVs MUST NOT be sent in LSPs; however, if one is received in an LSP,
it is processed normally.
8.1.1. Backward Compatibility
A TRILL campus might contain TRILL switches supporting E-L1FS
flooding and legacy TRILL switches that do not support E-L1FS or
perhaps do not support any [RFC7356] scopes.
A TRILL switch conformant to this document can always tell which
adjacent TRILL switches support E-L1FS flooding from the adjacency
table entries on its ports (see Section 9). In addition, such a
TRILL switch can tell which remote TRILL switches in a campus support
E-L1FS by the presence of a TRILL version sub-TLV in that TRILL
switch's LSP with the E-L1FS support bit set in the Capabilities
field; this capability bit is ignored for adjacent TRILL switches for
which only the adjacency table entry is consulted to determine E-L1FS
support.
Eastlake, et al. Standards Track [Page 24]
RFC 7780 TRILL Clarifications, Corrections, Updates February 2016
TRILL specifications making use of E-L1FS MUST specify how situations
involving a mixed TRILL campus of TRILL switches will be handled.
8.1.2. E-L1FS Use for Existing (Sub-)TLVs
In a campus where all TRILL switches support E-L1FS, all TRILL
sub-TLVs listed in Section 2.3 of [RFC7176], except the TRILL version
sub-TLV, MAY be advertised by inclusion in Router Capability or
MT-Capability TLVs in E-L1FS FS-LSPs [RFC7356]. (The TRILL version
sub-TLV still MUST appear in an LSP fragment zero.)
In a mixed campus where some TRILL switches support E-L1FS and some
do not, then only the following four sub-TLVs of those listed in
Section 2.3 of [RFC7176] can appear in E-L1FS, and then only under
the conditions discussed below. In the following list, each sub-TLV
is preceded by an abbreviated acronym used only in this section of
this document:
IV: Interested VLANs and Spanning Tree Roots sub-TLV
VG: VLAN Group sub-TLV
IL: Interested Labels and Spanning Tree Roots sub-TLV
LG: Label Group sub-TLV
An IV or VG sub-TLV MUST NOT be advertised by TRILL switch RB1 in an
E-L1FS FS-LSP (and should instead be advertised in an LSP) unless the
following conditions are met:
- E-L1FS is supported by all of the TRILL switches that are data
reachable from RB1 and are interested in the VLANs mentioned in the
IV or VG sub-TLV, and
- there is E-L1FS connectivity between all such TRILL switches in the
campus interested in the VLANs mentioned in the IV or VG sub-TLV
(connectivity involving only intermediate TRILL switches that also
support E-L1FS).
Any IV and VG sub-TLVs MAY still be advertised via core TRILL IS-IS
LSPs by any TRILL switch that has enough room in its LSPs.
The conditions for using E-L1FS for the IL and LG sub-TLVs are the
same as for IV and VG, but with Fine-Grained Labels [RFC7172]
substituted for VLANs.
Note, for example, that the above would permit a contiguous subset
of the campus that supported Fine-Grained Labels and E-L1FS to use
E-L1FS to advertise IL and LG sub-TLVs, even if the remainder of
the campus did not support Fine-Grained Labels or E-L1FS.
Eastlake, et al. Standards Track [Page 25]
RFC 7780 TRILL Clarifications, Corrections, Updates February 2016
8.2. Control Packet Priorities (New)
When deciding what packet to send out a port, control packets used to
establish and maintain adjacency between TRILL switches SHOULD be
treated as being in the highest-priority category. This includes
TRILL IS-IS Hello and MTU PDUs, and possibly other adjacency
[RFC7177] or link-technology-specific packets. Other control and
data packets SHOULD be given lower priority so that a flood of such
other packets cannot lead to loss of, or inability to establish,
adjacency. Loss of adjacency causes a topology transient that can
result in reduced throughput; reordering; increased probability of
loss of data; and, in the worst case, network partition if the
adjacency is a cut point.
Other important control packets should be given second-highest
priority. Lower priorities should be given to data or less important
control packets.
Based on the above, control packets can be ordered into priority
categories as shown below, based on the relative criticality of these
types of messages, where the most critical control packets relate to
the core routing between TRILL switches and the less critical control
packets are closer to "application" information. (There may be
additional control packets, not specifically listed in any category
below, that SHOULD be handled as being in the most nearly analogous
category.) Although few implementations will actually treat these
four categories with different priority, an implementation MAY choose
to prioritize more critical messages over less critical. However, an
implementation SHOULD NOT send control packets in a lower-priority
category with a priority above those in a higher-priority category
because, under sufficiently congested conditions, this could block
control packets in a higher-priority category, resulting in network
disruption.
Priority
Category Description
-------- --------------
4. Hello, MTU-probe, MTU-ack, and other packets critical
to establishing and maintaining adjacency. (Normally
sent with highest priority, which is priority 7.)
3. LSPs, CSNPs/PSNPs, and other important control packets.
2. Circuit scoped FS-LSPs, FS-CSNPs, and FS-PSNPs.
1. Non-circuit scoped FS-LSPs, FS-CSNPs, and FS-PSNPs.
Eastlake, et al. Standards Track [Page 26]
RFC 7780 TRILL Clarifications, Corrections, Updates February 2016
8.3. Unknown PDUs (New)
TRILL switches MUST silently discard [IS-IS] PDUs they receive with
PDU numbers they do not understand, just as they ignore TLVs and
sub-TLVs they receive that have unknown Types and sub-Types; however,
they SHOULD maintain a counter of how many such PDUs have been
received, on a per-PDU-number basis. (This is not burdensome, as the
PDU number is only a 5-bit field.)
Note: The set of valid [IS-IS] PDUs was stable for so long that
some IS-IS implementations may treat PDUs with unknown PDU
numbers as a serious error and, for example, an indication that
other valid PDUs from the sender are not to be trusted or that
they should drop adjacency to the sender if it was adjacent.
However, the MTU-probe and MTU-ack PDUs were added by
[RFC7176], and now [RFC7356] has added three more new PDUs.
Although the authors of this document are not aware of any
Internet-Drafts calling for further PDUs, the eventual addition
of further new PDUs should not be surprising.
8.4. Nickname Flags APPsub-TLV (New)
An optional Nickname Flags APPsub-TLV within the TRILL GENINFO TLV
[RFC7357] is specified below.
1 1 1 1 1 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = NickFlags (6) | (2 bytes)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length = 4*K | (2 bytes)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NICKFLAG RECORD 1 (4 bytes) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NICKFLAG RECORD K (4 bytes) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where each NICKFLAG RECORD has the following format:
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| Nickname |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
|IN| RESV |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
Eastlake, et al. Standards Track [Page 27]
RFC 7780 TRILL Clarifications, Corrections, Updates February 2016
o Type: NickFlags TRILL APPsub-TLV, set to 6 (NICKFLAGS).
o Length: 4 times the number of NICKFLAG RECORDS present.
o Nickname: A 16-bit TRILL nickname held by the advertising TRILL
switch ([RFC6325] and Section 4).
o IN: Ingress. If this flag is one, it indicates that the
advertising TRILL switch may use the nickname in the NICKFLAG
RECORD as the Ingress Nickname of TRILL Headers it creates. If
the flag is zero, that nickname will not be used for that
purpose.
o RESV: Reserved for additional flags to be specified in the
future. MUST be sent as zero and ignored on receipt.
The entire NickFlags APPsub-TLV is ignored if the Length is not a
multiple of 4. A NICKFLAG RECORD is ignored if the nickname it lists
is not a nickname owned by the TRILL switch advertising the enclosing
NickFlags APPsub-TLV.
If a TRILL switch intends to use a nickname in the Ingress Nickname
field of TRILL Headers it constructs, it can advertise this through
E-L1FS FS-LSPs (see Section 8.1) using a NickFlags APPsub-TLV entry
with the IN flag set. If it owns only one nickname, there is no
reason to do this because, if a TRILL switch advertises no NickFlags
APPsub-TLVs with the IN flag set for nicknames it owns, it is assumed
that the TRILL switch might use any or all nicknames it owns as the
Ingress Nickname in TRILL Headers it constructs. If a TRILL switch
advertises any NickFlags APPsub-TLV entries with the IN flag set,
then it MUST NOT use any other nickname(s) it owns as the Ingress
Nickname in TRILL Headers it constructs.
Every reasonable effort should be made to be sure that Nickname
sub-TLVs [RFC7176] and NickFlags APPsub-TLVs remain in sync. If all
TRILL switches in a campus support E-L1FS, so that Nickname sub-TLVs
can be advertised in E-L1FS FS-LSPs, then the Nickname sub-TLV and
any NickFlags APPsub-TLVs for any particular nickname SHOULD be
advertised in the same fragment. If they are not in the same
fragment, then, to the extent practical, all fragments involving
those sub-TLVs for the same nickname should be propagated as an
atomic action. If a TRILL switch sees multiple NickFlags APPsub-TLV
entries for the same nickname, it assumes that that nickname might be
used as the ingress in a TRILL Header if any of the NickFlags
APPsub-TLV entries have the IN bit set.
Eastlake, et al. Standards Track [Page 28]
RFC 7780 TRILL Clarifications, Corrections, Updates February 2016
It is possible that a NickFlags APPsub-TLV would not be propagated
throughout the TRILL campus due to legacy TRILL switches not
supporting E-L1FS. In that case, Nickname sub-TLVs MUST be
advertised in LSPs, and TRILL switches not receiving NickFlags
APPsub-TLVs having entries with the IN flag set will simply assume
that the source TRILL switch might use any of its nicknames as the
ingress in constructing TRILL Headers. Thus, the use of this
optional APPsub-TLV is backward compatible with legacy lack of E-L1FS
support.
(Additional flags are assigned from those labeled RESV above and
specified in [TRILL-L3-GW] and [Centralized-Replication].)
8.5. Graceful Restart (Unchanged)
TRILL switches SHOULD support the features specified in [RFC5306],
which describes a mechanism for a restarting IS-IS router to signal
to its neighbors that it is restarting, allowing them to reestablish
their adjacencies without cycling through the down state, while still
correctly initiating link-state database synchronization. If this
feature is not supported, it may increase the number of topology
transients caused by a TRILL switch rebooting due to errors or
maintenance.
8.6. Purge Originator Identification (New)
To ease debugging of any purge-related problems, TRILL switches
SHOULD include the Purge Originator Identification TLV [RFC6232] in
all purge PDUs in TRILL IS-IS. This includes Flooding Scope LSPs
[RFC7356] and ESADI LSPs [RFC7357].
Eastlake, et al. Standards Track [Page 29]
RFC 7780 TRILL Clarifications, Corrections, Updates February 2016
9. Updates to RFC 7177 (Adjacency) (Changed)
To support the E-L1FS flooding scope [RFC7356] mandated by
Section 8.1 and backward compatibility with legacy RBridges not
supporting E-L1FS flooding, this document updates [RFC7177] as
follows:
1. The list in the second paragraph of Section 3.1 of [RFC7177] is
updated by adding the following item:
o The Scope Flooding Support TLV.
In addition, the sentence immediately after that list is updated
by this document to read as follows:
Of course, (a) the priority, (b) the Desired Designated VLAN,
(c) the Scope Flooding Support TLV, and whether or not the
(d) PORT-TRILL-VER sub-TLV and/or (e) BFD-Enabled TLV are
included, and their value if included, could change on
occasion. However, if these change, the new value(s) must
similarly be used in all TRILL Hellos on the LAN port,
regardless of VLAN.
2. This document adds another bullet item to the end of Section 3.2
of [RFC7177], as follows:
o The value from the Scope Flooding Support TLV, or a null string
if none was included.
3. Near the bottom of Section 3.3 of [RFC7177], this document adds
the following bullet item:
o The variable-length value part of the Scope Flooding Support
TLV in the Hello, or a null string if that TLV does not occur
in the Hello.
4. At the beginning of Section 4 of [RFC7177], this document adds a
bullet item to the list, as follows:
o The variable-length value part of the Scope Flooding Support
TLV used in TRILL Hellos sent on the port.
Eastlake, et al. Standards Track [Page 30]
RFC 7780 TRILL Clarifications, Corrections, Updates February 2016
5. This document adds a line to Table 4 ("TRILL Hello Contents") in
Section 8.1 of [RFC7177], as follows:
LAN P2P Number Content Item
--- --- ------ ---------------------------
M M 1 Scope Flooding Support TLV
10. TRILL Header Update (New)
The TRILL Header has been updated from its original specification in
[RFC6325] by [RFC7455] and [RFC7179] and is further updated by this
document. The TRILL Header is now as shown in the figure below
(which is followed by references for all of the fields). Those
fields for which the reference is only to [RFC6325] are unchanged
from that RFC.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| V |A|C|M| RESV |F| Hop Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Egress Nickname | Ingress Nickname |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Optional Flags Word :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
In calculating a TRILL Data packet hash as part of equal-cost
multipath selection, a TRILL switch MUST ignore the value of the
"A" and "C" bits.
In [RFC6325] and [RFC7179], there is a TRILL Header Extension Length
field called "Op-Length", which is hereby changed to consist of the
RESV field and "F" bit shown above.
o V (Version): 2-bit unsigned integer. See Section 3.2
of [RFC6325].
o A (Alert): 1 bit. See [RFC7455].
o C (Color): 1 bit. See Section 10.1.
o M (Multi-destination): 1 bit. See Section 3.4 of [RFC6325].
o RESV: 4 bits. These bits are reserved and MUST be sent as zero.
Due to the previous use of these bits as specified in [RFC6325],
most TRILL "fast path" hardware implementations trap and do not
forward TRILL Data packets with these bits non-zero. A TRILL
Eastlake, et al. Standards Track [Page 31]
RFC 7780 TRILL Clarifications, Corrections, Updates February 2016
switch receiving a TRILL Data packet with any of these bits
non-zero MUST discard the packet unless the non-zero bit or bits
have some future use specified that the TRILL switch understands.
o F: 1 bit. If this field is non-zero, then the optional flags word
described in Section 10.2 is present. If it is zero, the
flags word is not present.
o Hop Count: 6 bits. See Section 3.6 of [RFC6325] and
Section 10.2.1 below.
o Egress Nickname: See Section 3.7.1 of [RFC6325].
o Ingress Nickname: See Section 3.7.2 of [RFC6325].
o Optional Flags Word: See [RFC7179] and Section 10.2.
10.1. Color Bit
The Color bit provides an optional way by which ingress TRILL
switches MAY mark TRILL Data packets for implementation-specific
purposes. Transit TRILL switches MUST NOT change this bit. Transit
and egress TRILL switches MAY use the Color bit for implementation-
dependent traffic labeling, or for statistical analysis or other
types of traffic study or analysis.
10.2. Flags Word Changes (Update to RFC 7179)
When the "F" bit in the TRILL Header is non-zero, the first 32 bits
after the Ingress Nickname field provide additional flags. These
bits are as specified in [RFC7179], except as changed by the
subsections below, in which the Extended Hop Count and Extended Color
fields are described. See Section 10.3 for a diagram and summary of
these fields.
10.2.1. Extended Hop Count
The TRILL base protocol [RFC6325] specifies the Hop Count field in
the header, to avoid packets persisting in the network due to looping
or the like. However, the Hop Count field size (6 bits) limits the
maximum hops a TRILL Data packet can traverse to 64. Optionally,
TRILL switches can use a field composed of bits 14 through 16 in the
flags word, as specified below, to extend this field to 9 bits. This
increases the maximum Hop Count to 512. Except in rare
circumstances, reliable use of Hop Counts in excess of 64 requires
support of this optional capability at all TRILL switches along the
path of a TRILL Data packet.
Eastlake, et al. Standards Track [Page 32]
RFC 7780 TRILL Clarifications, Corrections, Updates February 2016
10.2.1.1. Advertising Support
It may be that not all the TRILL switches support the Extended Hop
Count mechanism in a TRILL campus and in that campus more than
64 hops are required either for the distribution tree calculated path
or for the unicast calculated path plus a reasonable allowance for
alternate pathing. As such, it is required that TRILL switches
advertise their support by setting bit 14 in the TRILL Version
Sub-TLV Capabilities and Header Flags Supported field [RFC7176];
bits 15 and 16 of that field are now specified as Unassigned (see
Section 12.2.5).
10.2.1.2. Ingress Behavior
If an ingress TRILL switch determines that it should set the
Hop Count for a TRILL Data packet to 63 or less, then behavior is as
specified in the TRILL base protocol [RFC6325]. If the optional
TRILL Header flags word is present, bits 14, 15, and 16 and the
critical reserved bit of the critical summary bits are zero.
If the Hop Count for a TRILL Data packet should be set to some value
greater than 63 but less than 512 and all TRILL switches that the
packet is reasonably likely to encounter support Extended Hop Count,
then the resulting TRILL Header has the flags word extension present,
the high-order 3 bits of the desired Hop Count are stored in the
Extended Hop Count field in the flags word, the low-order 5 bits are
stored in the Hop Count field in the first word of the TRILL Header,
and bit two (the critical reserved bit of the critical summary bits)
in the flags word is set to one.
For known unicast traffic (TRILL Header "M" bit zero), an ingress
TRILL switch discards the frame if it determines that the least-cost
path to the egress is (1) more than 64 hops and not all TRILL
switches on that path support the Extended Hop Count feature or
(2) more than 512 hops.
For multi-destination traffic, when a TRILL switch determines that
one or more tree paths from the ingress are more than 64 hops and not
all TRILL switches in the campus support the Extended Hop Count
feature, the encapsulation uses a total Hop Count of 63 to obtain at
least partial distribution of the traffic.
10.2.1.3. Transit Behavior
A transit TRILL switch supporting Extended Hop Count behaves like a
base protocol [RFC6325] TRILL switch in decrementing the Hop Count,
except that it considers the Hop Count to be a 9-bit field where the
Extended Hop Count field constitutes the high-order 3 bits.
Eastlake, et al. Standards Track [Page 33]
RFC 7780 TRILL Clarifications, Corrections, Updates February 2016
To be more precise: a TRILL switch supporting Extended Hop Count
takes the first of the following actions that is applicable:
1. If both the Hop Count and Extended Hop Count fields are zero, the
packet is discarded.
2. If the Hop Count is non-zero, it is decremented. As long as the
Extended Hop Count is non-zero, no special action is taken. If
the result of this decrement is zero, the packet is processed
normally.
3. If the Hop Count is zero, it is set to the maximum value of 63,
and the Extended Hop Count is decremented. If this results in the
Extended Hop Count being zero, the critical reserved bit in the
critical summary bits is set to zero.
10.2.1.4. Egress Behavior
No special behavior is required when egressing a TRILL Data packet
that uses the Extended Hop Count. The flags word, if present, is
removed along with the rest of the TRILL Header during decapsulation.
10.2.2. Extended Color Field
Flags word bits 27 and 28 are specified to be a 2-bit Extended Color
field (see Section 10.3). These bits are in the non-critical
ingress-to-egress region of the flags word.
The Extended Color field provides an optional way by which ingress
TRILL switches MAY mark TRILL Data packets for implementation-
specific purposes. Transit TRILL switches MUST NOT change these
bits. Transit and egress TRILL switches MAY use the Extended Color
bits for implementation-dependent traffic labeling, or for
statistical analysis or other types of traffic study or analysis.
Per Section 2.3.1 of [RFC7176], support for these bits is indicated
by the same bits (27 and 28) in the Capabilities and Header Flags
Supported field of the TRILL version sub-TLV. If these bits are zero
in those capabilities, Extended Color is not supported. A TRILL
switch that does not support Extended Color will ignore the
corresponding bits in any TRILL Header flags word it receives as part
of a TRILL Data packet and will set those bits to zero in any TRILL
Header flags word it creates. A TRILL switch that sets or senses the
Extended Color field on transmitting or receiving TRILL Data packets
MUST set the corresponding 2-bit field in the TRILL version sub-TLV
to a non-zero value. Any difference in the meaning of the three
possible non-zero values of this 2-bit capability field (0b01, 0b10,
or 0b11) is implementation dependent.
Eastlake, et al. Standards Track [Page 34]
RFC 7780 TRILL Clarifications, Corrections, Updates February 2016
10.3. Updated Flags Word Summary
With the changes above, the 32-bit flags word extension to the TRILL
Header [RFC7179], which is detailed in the "TRILL Extended Header
Flags" registry on the "Transparent Interconnection of Lots of Links
(TRILL) Parameters" IANA web page, is now as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Crit.| CHbH | NCHbH |CRSV | NCRSV | CItE | NCItE |
|.....|.........|...........|.....|.......|...........|.........|
|C|C|C| |C|N| | Ext | | |Ext| |
|R|R|R| |R|C| | Hop | | |Clr| |
|H|I|R| |C|C| | Cnt | | | | |
|b|t|s| |A|A| | | | | | |
|H|E|v| |F|F| | | | | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Bits 0, 1, and 2 are the critical summary bits, as specified in
[RFC7179], consisting of the critical hop-by-hop, critical
ingress-to-egress, and critical reserved bits, respectively. The
next two fields are specific critical and non-critical hop-by-hop
bits -- CHbH and NCHbH, respectively -- containing the Critical and
Non-critical Channel Alert flags as specified in [RFC7179]. The next
field is the critical reserved bits (CRSV), which are specified
herein to be the Extended Hop Count. The non-critical reserved bits
(NCRSV) and the critical ingress-to-egress bits (CItE) as specified
in [RFC7179] follow. Finally, there is the non-critical
ingress-to-egress field, including bits 27 and 28, which are
specified herein as the Extended Color field.
11. Appointed Forwarder Status Lost Counter (New)
Strict conformance to the provisions of Section 4.8.3 of [RFC6325] on
the value of the Appointed Forwarder Status Lost Counter can result
in the splitting of Interested VLANs and Spanning Tree Roots sub-TLVs
[RFC7176] (or the corresponding Interested Labels and Spanning Tree
Roots sub-TLVs where a VLAN is mapped to an FGL) due to differences
in this counter value for adjacent VLAN IDs (or 24-bit FGLs). This
counter is a mechanism to optimize data-plane learning by trimming
the expiration timer for learned addresses on a per-VLAN/FGL basis
under some circumstances.
The requirement to increment this counter by one whenever a TRILL
switch loses Appointed Forwarder status on a port is hereby changed
from the mandatory provisions of [RFC6325] to the enumerated
provisions below. To the extent that this might cause the Appointed
Eastlake, et al. Standards Track [Page 35]
RFC 7780 TRILL Clarifications, Corrections, Updates February 2016
Forwarder Status Lost Counter to be increased when [RFC6325]
indicates that it should not, this will cause data-plane address
learning timeouts at remote TRILL switches to be reduced. To the
extent that this might cause the Appointed Forwarder Status Lost
Counter to remain unchanged when [RFC6325] indicates that it should
be increased, this will defeat a reduction in such timeouts that
would otherwise occur.
(1) If any of the following apply, either data-plane address learning
is not in use or Appointed Forwarder status is irrelevant. In
these cases, the Appointed Forwarder Status Lost Counter MAY be
left at zero or set to any convenient value such as the value of
the Appointed Forwarder Status Lost Counter for an adjacent
VLAN ID or FGL.
(1a) The TRILL switch port has been configured with the
"end-station service disable" bit (also known as the
trunk bit) on.
(1b) The TRILL switch port has been configured in IS-IS as an
IS-IS point-to-point link.
(1c) The TRILL switch is relying on ESADI [RFC7357] or Directory
Assist [RFC7067] and not using data-plane learning.
(2) In cases other than those enumerated in point 1 above, the
Appointed Forwarder Status Lost Counter SHOULD be incremented as
described in [RFC6325]. Such incrementing has the advantage of
optimizing data-plane learning. Alternatively, the value of the
Appointed Forwarder Status Lost Counter can deviate from that
value -- for example, to make it match the value for an adjacent
VLAN ID (or FGL), so as to permit greater aggregation of
Interested VLANs and Spanning Tree Roots sub-TLVs.
Eastlake, et al. Standards Track [Page 36]
RFC 7780 TRILL Clarifications, Corrections, Updates February 2016
12. IANA Considerations (Changed)
This section lists IANA actions previously completed and new IANA
actions.
12.1. Previously Completed IANA Actions (Unchanged)
The following IANA actions were completed as part of [RFC7180] and
are included here for completeness, since this document obsoletes
[RFC7180].
1. The nickname 0xFFC1, which was reserved by [RFC6325], is allocated
for use in the TRILL Header Egress Nickname field to indicate an
OOMF (Overload Originated Multi-destination Frame).
2. Bit 1 from the seven previously reserved (RESV) bits in the
per-neighbor "Neighbor RECORD" in the TRILL Neighbor TLV [RFC7176]
is allocated to indicate that the RBridge sending the TRILL Hello
volunteers to provide the OOMF forwarding service described in
Section 2.4.2 to such frames originated by the TRILL switch whose
SNPA (MAC address) appears in that Neighbor RECORD. The
description of this bit is "Offering OOMF service".
3. Bit 0 is allocated from the capability bits in the PORT-TRILL-VER
sub-TLV [RFC7176] to indicate support of the VLANs Appointed
sub-TLV [RFC7176] and the VLAN inhibition setting mechanisms
specified in [RFC6439bis]. The description of this bit is "Hello
reduction support".
12.2. New IANA Actions (New)
The following are new IANA actions for this document.
12.2.1. Reference Updated
All references to [RFC7180] in the "Transparent Interconnection of
Lots of Links (TRILL) Parameters" registry have been replaced with
references to this document, except that the Reference for bit 0 in
the PORT-TRILL-VER Sub-TLV Capability Flags has been changed to
[RFC6439bis].
12.2.2. The "E" Capability Bit
There is an existing TRILL version sub-TLV, sub-TLV #13, under both
TLV #242 and TLV #144 [RFC7176]. This TRILL version sub-TLV contains
a capability bits field for which assignments are documented in the
"TRILL-VER Sub-TLV Capability Flags" registry on the TRILL Parameters
IANA web page. IANA has allocated 4 from the previously reserved
Eastlake, et al. Standards Track [Page 37]
RFC 7780 TRILL Clarifications, Corrections, Updates February 2016
bits in this "TRILL-VER Sub-TLV Capability Flags" registry to
indicate support of the E-L1FS flooding scope as specified in
Section 8.1. This capability bit is referred to as the "E" bit. The
following is the addition to the "TRILL-VER Sub-TLV Capability Flags"
registry:
Bit Description References
---- --------------------- ---------------
4 E-L1FS FS-LSP support [RFC7356], RFC 7780
12.2.3. NickFlags APPsub-TLV Number and Registry
IANA has assigned an APPsub-TLV number, as follows, under the TRILL
GENINFO TLV from the range less than 255.
Type Name References
---- --------- -----------
6 NICKFLAGS RFC 7780
In addition, IANA has created a registry on its TRILL Parameters web
page for NickFlags bit assignments, as follows:
Name: NickFlags Bits
Registration Procedure: IETF Review [RFC5226]
Reference: RFC 7780
Bit Mnemonic Description Reference
----- -------- ----------- ---------
0 IN Used as ingress RFC 7780
1-15 - Unassigned RFC 7780
12.2.4. Updated TRILL Extended Header Flags
The "TRILL Extended Header Flags" registry has been updated as
follows:
Bits Purpose Reference
----- ---------------------------------------- ------------
14-16 Extended Hop Count RFC 7780
27-28 Extended Color RFC 7780
29-31 Available non-critical ingress-to-egress [RFC7179], RFC 7780
flags
Eastlake, et al. Standards Track [Page 38]
RFC 7780 TRILL Clarifications, Corrections, Updates February 2016
12.2.5. TRILL-VER Sub-TLV Capability Flags
The "TRILL-VER Sub-TLV Capability Flags" registry has been updated as
follows:
Bit Description Reference
----- -------------------------- ----------------
14 Extended Hop Count support RFC 7780
15-16 Unassigned RFC 7780
27-28 Extended Color support RFC 7780
29-31 Extended header flag support [RFC7179], RFC 7780
12.2.6. Example Nicknames
As shown in the table below, IANA has assigned a block of eight
nicknames for use as examples in documentation. Appendix B shows a
use of some of these nicknames. The "TRILL Nicknames" registry has
been updated by changing the previous "0xFFC2-0xFFFE Unassigned" line
to the following:
Name Description Reference
------------- -------------- -----------
0xFFC2-0xFFD7 Unassigned
0xFFD8-0xFFDF For use in documentation examples RFC 7780
0xFFE0-0xFFFE Unassigned
13. Security Considerations (Changed)
See [RFC6325] for general TRILL security considerations.
This memo improves the documentation of the TRILL protocol; corrects
six errata in [RFC6325]; updates [RFC6325], [RFC7177], and [RFC7179];
and obsoletes [RFC7180]. It does not change the security
considerations of those RFCs, except as follows:
o E-L1FS FS-LSPs can be authenticated with IS-IS security [RFC5310],
that is, through the inclusion of an IS-IS Authentication TLV in
E-L1FS PDUs.
o As discussed in Section 3.6, when using an allowed weaker RPF
check under very rare topologies and transient conditions,
multi-destination TRILL Data packets can be duplicated; this could
have security consequences for some protocols.
Eastlake, et al. Standards Track [Page 39]
RFC 7780 TRILL Clarifications, Corrections, Updates February 2016
14. References
14.1. Normative References
[802.1Q-2014]
IEEE, "IEEE Standard for Local and metropolitan area
networks -- Bridges and Bridged Networks",
DOI 10.1109/IEEESTD.2014.6991462, IEEE Std 802.1Q-2014.
[IS-IS] International Organization for Standardization,
"Information technology -- Telecommunications and
information exchange between systems -- Intermediate
System to Intermediate System intra-domain routeing
information exchange protocol for use in conjunction with
the protocol for providing the connectionless-mode network
service (ISO 8473)", ISO/IEC 10589:2002, Second Edition,
November 2002.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic
Engineering", RFC 5305, DOI 10.17487/RFC5305,
October 2008, <http://www.rfc-editor.org/info/rfc5305>.
[RFC5306] Shand, M. and L. Ginsberg, "Restart Signaling for IS-IS",
RFC 5306, DOI 10.17487/RFC5306, October 2008,
<http://www.rfc-editor.org/info/rfc5306>.
[RFC5310] Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R.,
and M. Fanto, "IS-IS Generic Cryptographic
Authentication", RFC 5310, DOI 10.17487/RFC5310,
February 2009, <http://www.rfc-editor.org/info/rfc5310>.
[RFC6232] Wei, F., Qin, Y., Li, Z., Li, T., and J. Dong, "Purge
Originator Identification TLV for IS-IS", RFC 6232,
DOI 10.17487/RFC6232, May 2011,
<http://www.rfc-editor.org/info/rfc6232>.
[RFC6325] Perlman, R., Eastlake 3rd, D., Dutt, D., Gai, S., and A.
Ghanwani, "Routing Bridges (RBridges): Base Protocol
Specification", RFC 6325, DOI 10.17487/RFC6325, July 2011,
<http://www.rfc-editor.org/info/rfc6325>.
Eastlake, et al. Standards Track [Page 40]
RFC 7780 TRILL Clarifications, Corrections, Updates February 2016
[RFC6361] Carlson, J. and D. Eastlake 3rd, "PPP Transparent
Interconnection of Lots of Links (TRILL) Protocol Control
Protocol", RFC 6361, DOI 10.17487/RFC6361, August 2011,
<http://www.rfc-editor.org/info/rfc6361>.
[RFC7172] Eastlake 3rd, D., Zhang, M., Agarwal, P., Perlman, R., and
D. Dutt, "Transparent Interconnection of Lots of Links
(TRILL): Fine-Grained Labeling", RFC 7172,
DOI 10.17487/RFC7172, May 2014,
<http://www.rfc-editor.org/info/rfc7172>.
[RFC7176] Eastlake 3rd, D., Senevirathne, T., Ghanwani, A., Dutt,
D., and A. Banerjee, "Transparent Interconnection of Lots
of Links (TRILL) Use of IS-IS", RFC 7176,
DOI 10.17487/RFC7176, May 2014,
<http://www.rfc-editor.org/info/rfc7176>.
[RFC7177] Eastlake 3rd, D., Perlman, R., Ghanwani, A., Yang, H., and
V. Manral, "Transparent Interconnection of Lots of Links
(TRILL): Adjacency", RFC 7177, DOI 10.17487/RFC7177,
May 2014, <http://www.rfc-editor.org/info/rfc7177>.
[RFC7179] Eastlake 3rd, D., Ghanwani, A., Manral, V., Li, Y., and C.
Bestler, "Transparent Interconnection of Lots of Links
(TRILL): Header Extension", RFC 7179,
DOI 10.17487/RFC7179, May 2014,
<http://www.rfc-editor.org/info/rfc7179>.
[RFC7356] Ginsberg, L., Previdi, S., and Y. Yang, "IS-IS Flooding
Scope Link State PDUs (LSPs)", RFC 7356,
DOI 10.17487/RFC7356, September 2014,
<http://www.rfc-editor.org/info/rfc7356>.
[RFC7455] Senevirathne, T., Finn, N., Salam, S., Kumar, D., Eastlake
3rd, D., Aldrin, S., and Y. Li, "Transparent
Interconnection of Lots of Links (TRILL): Fault
Management", RFC 7455, DOI 10.17487/RFC7455, March 2015,
<http://www.rfc-editor.org/info/rfc7455>.
Eastlake, et al. Standards Track [Page 41]
RFC 7780 TRILL Clarifications, Corrections, Updates February 2016
14.2. Informative References
[802] IEEE 802, "IEEE Standard for Local and Metropolitan Area
Networks: Overview and Architecture",
DOI 10.1109/IEEESTD.2014.6847097, IEEE Std 802-2014.
[Centralized-Replication]
Hao, W., Li, Y., Durrani, M., Gupta, S., Qu, A., and T.
Han, "Centralized Replication for BUM traffic in
active-active edge connection", Work in Progress,
draft-ietf-trill-centralized-replication-03,
November 2015.
[Err3002] RFC Errata, Erratum ID 3002, RFC 6325.
[Err3003] RFC Errata, Erratum ID 3003, RFC 6325.
[Err3004] RFC Errata, Erratum ID 3004, RFC 6325.
[Err3052] RFC Errata, Erratum ID 3052, RFC 6325.
[Err3053] RFC Errata, Erratum ID 3053, RFC 6325.
[Err3508] RFC Errata, Erratum ID 3508, RFC 6325.
[RFC792] Postel, J., "Internet Control Message Protocol", STD 5,
RFC 792, DOI 10.17487/RFC0792, September 1981,
<http://www.rfc-editor.org/info/rfc792>.
[RFC826] Plummer, D., "Ethernet Address Resolution Protocol: Or
Converting Network Protocol Addresses to 48.bit Ethernet
Address for Transmission on Ethernet Hardware", STD 37,
RFC 826, DOI 10.17487/RFC0826, November 1982,
<http://www.rfc-editor.org/info/rfc826>.
[RFC4086] Eastlake 3rd, D., Schiller, J., and S. Crocker,
"Randomness Requirements for Security", BCP 106, RFC 4086,
DOI 10.17487/RFC4086, June 2005,
<http://www.rfc-editor.org/info/rfc4086>.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
DOI 10.17487/RFC5226, May 2008,
<http://www.rfc-editor.org/info/rfc5226>.
Eastlake, et al. Standards Track [Page 42]
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[RFC6327] Eastlake 3rd, D., Perlman, R., Ghanwani, A., Dutt, D., and
V. Manral, "Routing Bridges (RBridges): Adjacency",
RFC 6327, DOI 10.17487/RFC6327, July 2011,
<http://www.rfc-editor.org/info/rfc6327>.
[RFC6439] Perlman, R., Eastlake, D., Li, Y., Banerjee, A., and F.
Hu, "Routing Bridges (RBridges): Appointed Forwarders",
RFC 6439, DOI 10.17487/RFC6439, November 2011,
<http://www.rfc-editor.org/info/rfc6439>.
[RFC6439bis]
Eastlake 3rd, D., Li, Y., Umair, M., Banerjee, A., and H.
Fangwei, "TRILL: Appointed Forwarders", Work in Progress,
draft-ietf-trill-rfc6439bis-01, January 2016.
[RFC7042] Eastlake 3rd, D. and J. Abley, "IANA Considerations and
IETF Protocol and Documentation Usage for IEEE 802
Parameters", BCP 141, RFC 7042, DOI 10.17487/RFC7042,
October 2013, <http://www.rfc-editor.org/info/rfc7042>.
[RFC7067] Dunbar, L., Eastlake 3rd, D., Perlman, R., and I.
Gashinsky, "Directory Assistance Problem and High-Level
Design Proposal", RFC 7067, DOI 10.17487/RFC7067,
November 2013, <http://www.rfc-editor.org/info/rfc7067>.
[RFC7175] Manral, V., Eastlake 3rd, D., Ward, D., and A. Banerjee,
"Transparent Interconnection of Lots of Links (TRILL):
Bidirectional Forwarding Detection (BFD) Support",
RFC 7175, DOI 10.17487/RFC7175, May 2014,
<http://www.rfc-editor.org/info/rfc7175>.
[RFC7178] Eastlake 3rd, D., Manral, V., Li, Y., Aldrin, S., and D.
Ward, "Transparent Interconnection of Lots of Links
(TRILL): RBridge Channel Support", RFC 7178,
DOI 10.17487/RFC7178, May 2014,
<http://www.rfc-editor.org/info/rfc7178>.
[RFC7180] Eastlake 3rd, D., Zhang, M., Ghanwani, A., Manral, V., and
A. Banerjee, "Transparent Interconnection of Lots of Links
(TRILL): Clarifications, Corrections, and Updates",
RFC 7180, DOI 10.17487/RFC7180, May 2014,
<http://www.rfc-editor.org/info/rfc7180>.
Eastlake, et al. Standards Track [Page 43]
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[RFC7357] Zhai, H., Hu, F., Perlman, R., Eastlake 3rd, D., and O.
Stokes, "Transparent Interconnection of Lots of Links
(TRILL): End Station Address Distribution Information
(ESADI) Protocol", RFC 7357, DOI 10.17487/RFC7357,
September 2014, <http://www.rfc-editor.org/info/rfc7357>.
[TRILL-L3-GW]
Hao, W., Li, Y., Qu, A., Durrani, M., Sivamurugan, P., and
L. Xia, "TRILL Distributed Layer 3 Gateway", Work in
Progress, draft-ietf-trill-irb-10, January 2016.
Eastlake, et al. Standards Track [Page 44]
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Appendix A. Life Cycle of a TRILL Switch Port (New)
Text from <http://www.ietf.org/mail-archive/web/trill/
current/msg06355.html> is paraphrased in this informational appendix.
Question:
Suppose we are developing a TRILL implementation to run on
different machines. Then what happens first? Is LSP flooding or
ESADI started first? -> Link-state database creation ->
Designated RBridge election (How to set priority? Any fixed
process that depends on user settings?) -> etc.
Answer:
The first thing that happens on a port/link is any link setup that
is needed. For example, on a PPP link [RFC6361], you need to
negotiate that you will be using TRILL. However, if you have
Ethernet links [RFC6325], which are probably the most common type,
there isn't any link setup needed.
As soon as the port is set up, it can ingress or egress native
frames if end-station service is being offered on that port.
Offering end-station service is the default. However, if the port
trunk bit (end-station service disable) is set or the port is
configured as an IS-IS point-to-point link port, then end-station
service is not offered; therefore, native frames received are
ignored, and native frames are not egressed.
TRILL IS-IS Hellos then get sent out the port to be exchanged with
any other TRILL switches on the link [RFC7177]. Only the Hellos
are required; optionally, you might also exchange MTU-probe/ack
PDUs [RFC7177], BFD PDUs [RFC7175], or other link test packets.
TRILL doesn't send any TRILL Data or TRILL IS-IS packets out the
port to the link, except for Hellos, until the link gets to the
2-Way or Report state [RFC7177].
If a link is configured as a point-to-point link, there is no
Designated RBridge (DRB) election. By default, an Ethernet link
is considered a LAN link, and the DRB election occurs when the
link is in any state other than Down. You don't have to configure
priorities for each TRILL switch (RBridge) to be the DRB. Things
will work fine with all the RBridges on a link using default
priority. But if the network manager wants to control this, there
should be a way for them to configure the priority to be the DRB
of the TRILL switch ports on the link.
Eastlake, et al. Standards Track [Page 45]
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(To avoid complexity, this appendix generally describes the
life cycle for a link that only has two TRILL switches on it. But
TRILL works fine as currently specified on a broadcast link with
multiple TRILL switches on it -- actually, multiple TRILL switch
ports -- since a TRILL switch can have multiple ports connected to
the same link. The most likely way to get such a multi-access
link with current technology and the existing TRILL standards is
to have more than two TRILL switch Ethernet ports connected to a
bridged LAN. The TRILL protocol operates above all bridging; in
general, the bridged LAN looks like a transparent broadcast link
to TRILL.)
When a link gets to the 2-Way or Report state, LSPs, CSNPs, and
PSNPs will start to flow on the link (as well as FS-LSPs,
FS-CSNPs, and FS-PSNPs for E-L1FS (see Section 8.1)).
When a link gets to the Report state, there is adjacency. The
existence of that adjacency is flooded (reported) to the campus in
LSPs. TRILL Data packets can then start to flow on the link as
TRILL switches recalculate the least-cost paths and distribution
trees to take the new adjacency into account. Until it gets to
the Report state, there is no adjacency, and no TRILL Data packets
can flow over that link (with the minor corner case exception that
an RBridge Channel message can, for its first hop only, be sent on
a port where there is no adjacency (Section 2.4 of [RFC7178]).
(Although this paragraph seems to be talking about link state, it
is actually port state. It is possible for different TRILL switch
ports on the same link to temporarily be in different states. The
adjacency state machinery runs independently on each port.)
ESADI [RFC7357] is built on top of the regular TRILL Data routing.
Since ESADI PDUs look, to transit TRILL switches, like regular
TRILL Data packets, no ESADI PDUs can flow until adjacencies are
established and TRILL Data is flowing. Of course, ESADI is
optional and is not used unless configured.
Eastlake, et al. Standards Track [Page 46]
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Question:
Does it require TRILL Full Headers at the time TRILL LSPs start
being broadcast on a link? Because at that time it's not defined
egress and ingress nicknames.
Answer:
TRILL Headers are only for TRILL Data packets. TRILL IS-IS
packets, such as TRILL LSPs, are sent in a different way that does
not use a TRILL Header and does not depend on nicknames.
Probably, in most implementations, a TRILL switch will start up
using the same nickname it had when it shut down or last got
disconnected from a campus. If you want, you can implement TRILL
to come up initially not reporting any nickname (by not including
a Nickname sub-TLV in its LSPs) until you get the link-state
database or most of the link-state database, and then choose a
nickname no other TRILL switch in the campus is using. Of course,
if a TRILL switch does not have a nickname, then it cannot ingress
data, cannot egress known unicast data, and cannot be a tree root.
TRILL IS-IS PDUs such as LSPs, and the link-state database, all
work based on the 7-byte IS-IS System ID (sometimes called the
LAN ID [IS-IS]). Since topology determination uses System IDs,
which are always unique across the campus, it is not affected by
the nickname assignment state. The nickname system is built on
top of that.
Eastlake, et al. Standards Track [Page 47]
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Appendix B. Example TRILL PDUs (New)
This appendix shows example TRILL IS-IS PDUs. The primary purpose of
these examples is to clarify issues related to bit ordering.
The examples in this appendix concentrate on the format of the packet
header and trailer. There are frequently unspecified optional items
or data in the packet that would affect header or trailer fields like
the packet length or checksum. Thus, an "Xed out" placeholder is
used for such fields, where each X represents one hex nibble.
B.1. LAN Hello over Ethernet
A TRILL Hello sent from a TRILL switch (RBridge) with 7-byte
System ID 0x30033003300300 holding nickname 0xFFDE over Ethernet from
a port with MAC address 0x00005E0053DE on VLAN 1 at priority 7.
There is one neighbor that is the DRB. The neighbor's port MAC is
0x00005E0053E3, and the neighbor's System ID is 0x44444444444400.
Ethernet Header
Outer.MacDA, Outer.MacSA
0x0180C2000041 All-IS-IS-RBridges Destination MAC Address
0x00005E0053DE Source MAC Address
Outer VLAN Tag (optional)
0x8100 C-VLAN Ethertype [802.1Q-2014]
0xE001 Priority 7, Outer.VLAN
IS-IS
0x22F4 L2-IS-IS Ethertype
IS-IS Payload
Common Header
0x83 Intradomain Routeing Protocol Discriminator
0x08 Header Length
0x01 IS-IS Version Number
0x06 ID Length of 6 Bytes
0x0F PDU Type (Level 1 LAN Hello)
0x01 Version
0x00 Reserved
0x01 Maximum Area Addresses
Hello PDU Specific Fields
0x01 Circuit Type (Level 1)
0x30033003300300 Source System ID
0x0009 Holding Time
0xXXXX PDU Length
0x40 Priority to be DRB
0x44444444444400 LAN ID
TLVs (the following order of TLVs or of sub-TLVs in a TLV
is not significant)
Eastlake, et al. Standards Track [Page 48]
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Area Addresses TLV
0x01 Area Addresses Type
0x02 Length of Value
0x01 Length of Address
0x00 The fixed TRILL Area Address
MT Port Capabilities TLV
0x8F MT Port Capabilities Type
0x0011 Length of Value
0x0000 Topology
Special VLANs and Flags Sub-TLV
0x01 Sub-TLV Type
0x08 Length
0x0123 Port ID
0xFFDE Sender Nickname
0x0001 Outer.VLAN
0x0001 Designated VLAN
Enabled VLANs Sub-TLV (optional)
0x02 Sub-TLV Type
0x03 Length
0x0001 Start VLAN 1
0x80 VLAN 1
TRILL Neighbor TLV
0x91 Neighbor Type
0x0A Length of Value
0xC0 S Flag = 1, L Flag = 1, SIZE field 0
NEIGHBOR RECORD
0x00 Flags
0x2328 MTU = 9 KB
0x00005E0053E3 Neighbor MAC Address
Scope Flooding Support TLV
0xF3 Scope Flooding Support Type
0x01 Length of Value
0x40 E-L1FS Flooding Scope
More TLVs (optional)
...
Ethernet Trailer
0xXXXXXXXX Ethernet Frame Check Sequence (FCS)
Eastlake, et al. Standards Track [Page 49]
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B.2. LSP over PPP
Here is an example of a TRILL LSP sent over a PPP link by the same
source TRILL switch as the example in Appendix B.1.
PPP Header
0x405D PPP TRILL Link State Protocol
IS-IS Payload
Common Header
0x83 Intradomain Routeing Protocol Discriminator
0x08 Header Length
0x01 IS-IS Version Number
0x06 ID Length of 6 Bytes
0x12 PDU Type (Level 1 LSP)
0x01 Version
0x00 Reserved
0x01 Maximum Area Addresses
LSP Specific Fields
0xXXXX PDU Length
0x0123 Remaining Lifetime
0x3003300330030009 LSP ID (fragment 9)
0x00001234 Sequence Number
0xXXXX Checksum
0x01 Flags = Level 1
TLVs (the following order of TLVs or of sub-TLVs in a TLV
is not significant)
Router Capability TLV
0xF2 Router Capability Type
0x0F Length of Value
0x00 Flags
Nickname Sub-TLV
0x06 Sub-TLV Type
0x05 Length of Value
NICKNAME RECORD
0x33 Nickname Priority
0x1234 Tree Root Priority
0xFFDE Nickname
TRILL Version Sub-TLV
0x0D Sub-TLV Type
0x05
0x00 Max Version
0x40000000 Flags = FGL Support
More TLVs (optional
...
PPP Trailer
0xXXXXXX PPP Frame Check Sequence (FCS)
Eastlake, et al. Standards Track [Page 50]
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B.3. TRILL Data over Ethernet
Below is an IPv4 ICMP Echo [RFC792] sent in a TRILL Data packet from
the TRILL switch that sent the Hello in Appendix B.1 to the neighbor
TRILL switch on the link used in Appendix B.1.
Ethernet Header
Outer.MacDA, Outer.MacSA
0x00005E0053E3 Destination MAC Address
0x00005E0053DE Source MAC Address
Outer VLAN Tag (optional)
0x8100 C-VLAN Ethertype [802.1Q-2014]
0x0001 Priority 0, Outer.VLAN 1
TRILL
0x22F3 TRILL Ethertype
TRILL Header
0X000E Flags, Hop Count 14
0xFFDF Egress Nickname
0xFFDC Ingress Nickname
Inner Ethernet Header
Inner.MacDA, Inner.MacSA
0x00005E005322 Destination MAC Address
0x00005E005344 Source MAC Address
Inner VLAN Tag
0x8100 C-VLAN Ethertype
0x0022 Priority 0, Inner.VLAN 34
Ethertype
0x0800 IPv4 Ethertype
IP Header
0x4500 Version 4, Header Length 5, ToS 0
0xXXXX Total Length
0x3579 Identification
0x0000 Flags, Fragment Offset
0x1101 TTL 17, ICMP = Protocol 1
0xXXXX Header Checksum
0xC0000207 Source IP 192.0.2.7
0xC000020D Destination IP 192.0.2.13
0x00000000 Options, Padding
ICMP
0x0800 ICMP Echo
0xXXXX Checksum
0x87654321 Identifier, Sequence Number
... Echo Data
Ethernet Trailer
0xXXXXXXXX Ethernet Frame Check Sequence (FCS)
Eastlake, et al. Standards Track [Page 51]
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B.4. TRILL Data over PPP
Below is an ARP Request [RFC826] sent in a TRILL Data packet from the
TRILL switch that sent the Hello in Appendix B.1 over a PPP link.
PPP Header
0x005D PPP TRILL Network Protocol
TRILL Header
0X080D Flags (M = 1), Hop Count 13
0xFFDD Distribution Tree Root Nickname
0xFFDC Ingress Nickname
Inner Ethernet Header
Inner.MacDA, Inner.MacSA
0xFFFFFFFFFFFF Destination MAC Address
0x00005E005344 Source MAC Address
Inner VLAN Tag
0x8100 C-VLAN Ethertype
0x0022 Priority 0, Inner.VLAN 34
Ethertype
0x0806 ARP Ethertype
ARP
0x0001 Hardware Address Space = Ethernet
0x0001 Protocol Address Space = IPv4
0x06 Size of Hardware Address
0x04 Size of Protocol Address
0x0001 OpCode = Request
0x00005E005344 Sender Hardware Address
0xC0000207 Sender Protocol Address 192.0.2.7
0x000000000000 Target Hardware Address
0xC000020D Target Protocol Address 192.0.2.13
PPP Trailer
0xXXXXXX PPP Frame Check Sequence (FCS)
Eastlake, et al. Standards Track [Page 52]
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Appendix C. Changes to Previous RFCs (New)
C.1. Changes to Obsoleted RFC 7180
This section summarizes the changes, augmentations, and excisions
this document specifies for [RFC7180], which it obsoletes and
replaces.
C.1.1. Changes
For each section header in this document ending with "(Changed)",
this section summarizes the changes that are made by this document:
Section 1 ("Introduction"): Numerous changes to reflect the overall
changes in contents.
Section 1.1 ("Precedence"): Changed to add mention of [RFC7179].
Section 1.3 ("Terminology and Acronyms"): Numerous terms added.
Section 3 ("Distribution Trees and RPF Check"): Changed by the
addition of the new material in Section 3.6. See Appendix C.1.2,
Item 1.
Section 8 ("Other IS-IS Considerations"): Changed by the addition of
Sections 8.1, 8.2, 8.3, and 8.4. See Appendix C.1.2 -- Items 2, 3,
4, and 5, respectively.
Section 9 ("Updates to RFC 7177 (Adjacency)": Changes and additions
to [RFC7177] to support E-L1FS. See Appendix C.1.2, Item 2.
Section 12 ("IANA Considerations"): Changed by the addition of
material in Section 12.2. See Appendix C.1.2, Item 7.
Section 13 ("Security Considerations"): Minor changes in the RFCs
listed.
C.1.2. Additions
This document contains the following material not present in
[RFC7180]:
1. Support for an alternative Reverse Path Forwarding Check (RPFC),
along with considerations for deciding between the original
[RFC6325] RPFC and this alternative RPFC. This alternative RPFC
was originally discussed on the TRILL WG mailing list in
<http://www.ietf.org/mail-archive/web/trill/current/
msg01852.html> and subsequent messages (Section 3.6).
Eastlake, et al. Standards Track [Page 53]
RFC 7780 TRILL Clarifications, Corrections, Updates February 2016
2. Mandatory E-L1FS [RFC7356] support (Sections 8.1 and 9).
3. Recommendations concerning control packet priorities
(Section 8.2).
4. Implementation requirements concerning unknown IS-IS PDU types
(Section 8.3).
5. Specification of an optional Nickname Flags APPsub-TLV and an
ingress flag within that APPsub-TLV (Section 8.4).
6. Update to the TRILL Header to allocate a Color bit
(Section 10.1), and update to the optional TRILL Header Extension
flags word to allocate a 2-bit Extended Color field
(Section 10.2).
7. Some new IANA Considerations in Section 12.2, including
reservation of nicknames for use as examples in documentation.
8. A new "Appointed Forwarder Status Lost Counter" section
(Section 11 of this document) that loosens the mandatory update
requirements specified in [RFC6325].
9. Informative Appendix A on the life cycle of a TRILL port.
10. A new Appendix B containing example TRILL PDUs.
11. Recommendation to use the Purge Originator Identification TLV
(Section 8.6).
C.1.3. Deletions
This document omits the following material that was present in
[RFC7180]:
1. All updates to [RFC6327] that occurred in [RFC7180]. These have
been rolled into [RFC7177], which obsoletes [RFC6327]. However,
new updates to [RFC7177] are included (see Appendix C.3).
2. All updates to [RFC6439]. These have been rolled into
[RFC6439bis], which is intended to obsolete [RFC6439].
Eastlake, et al. Standards Track [Page 54]
RFC 7780 TRILL Clarifications, Corrections, Updates February 2016
C.2. Changes to RFC 6325
This document contains many normative updates to [RFC6325], some of
which were also in [RFC7180], which this document replaces. These
changes include the following:
1. Changing nickname allocation to ignore conflicts with RBridges
that are IS-IS unreachable.
2. Fixing errors: [Err3002], [Err3003], [Err3004], [Err3052],
[Err3053], and [Err3508].
3. Changing the requirement to use the RPF check described in
[RFC6325] for multi-destination TRILL Data packets by providing
an alternative stronger RPF check.
4. Adoption of the change of the CFI bit, which was required to be
zero in the inner frame, to the DEI bit, which is obtained from
inner frame ingress or creation.
5. Requiring that all RBridges support E-L1FS FS-LSP flooding.
6. Reducing the variable-length TRILL Header extensions area to one
optional flags word. The Extension Length field (called
"Op-Length" in [RFC6325]) is reduced to 1 bit that indicates
whether the flags word is present. The rest of that Length field
is now reserved.
7. Changing the mandatory Appointed Forwarder Status Lost Counter
increment provisions, as specified in Section 11.
C.3. Changes to RFC 7177
All of the updates to [RFC7177] herein are in Section 9. Basically,
this document requires that a Scope Flooding Support TLV [RFC7356]
appear in all Hellos and that TRILL switches retain in their
adjacency state the information received in that TLV.
C.4. Changes to RFC 7179
The updates to [RFC7179] herein are in Sections 10.2 and 10.3.
Eastlake, et al. Standards Track [Page 55]
RFC 7780 TRILL Clarifications, Corrections, Updates February 2016
Acknowledgments
The contributions of the following individuals to this document are
gratefully acknowledged:
Santosh Rajagopalan and Gayle Noble
The contributions of the following (listed in alphabetical order) to
the preceding version of this document, [RFC7180], are gratefully
acknowledged:
Somnath Chatterjee, Weiguo Hao, Rakesh Kumar, Yizhou Li, Radia
Perlman, Varun Shah, Mike Shand, and Meral Shirazipour.
Authors' Addresses
Donald Eastlake 3rd
Huawei Technology
155 Beaver Street
Milford, MA 01757
United States
Phone: +1-508-333-2270
Email: d3e3e3@gmail.com
Mingui Zhang
Huawei Technologies
No. 156 Beiqing Rd., Haidian District
Beijing 100095
China
Email: zhangmingui@huawei.com
Radia Perlman
EMC
2010 256th Avenue NE, #200
Bellevue, WA 98007
United States
Email: radia@alum.mit.edu
Ayan Banerjee
Cisco
Email: ayabaner@cisco.com
Eastlake, et al. Standards Track [Page 56]
RFC 7780 TRILL Clarifications, Corrections, Updates February 2016
Anoop Ghanwani
Dell
5450 Great America Parkway
Santa Clara, CA 95054
United States
Email: anoop@alumni.duke.edu
Sujay Gupta
IP Infusion
RMZ Centennial
Mahadevapura Post
Bangalore 560048
India
Email: sujay.gupta@ipinfusion.com
Eastlake, et al. Standards Track [Page 57]