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Internet Engineering Task Force (IETF) V. Moreno
Request for Comments: 8378 Cisco Systems
Category: Experimental D. Farinacci
ISSN: 2070-1721 lispers.net
May 2018
Signal-Free Locator/ID Separation Protocol (LISP) Multicast
Abstract
When multicast sources and receivers are active at Locator/ID
Separation Protocol (LISP) sites, the core network is required to use
native multicast so packets can be delivered from sources to group
members. When multicast is not available to connect the multicast
sites together, a signal-free mechanism can be used to allow traffic
to flow between sites. The mechanism described in this document uses
unicast replication and encapsulation over the core network for the
data plane and uses the LISP mapping database system so encapsulators
at the source LISP multicast site can find decapsulators at the
receiver LISP multicast sites.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for examination, experimental implementation, and
evaluation.
This document defines an Experimental Protocol for the Internet
community. 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). Not
all documents approved by the IESG are candidates for any level of
Internet Standard; see Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc8378.
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RFC 8378 Signal-Free LISP Multicast May 2018
Copyright Notice
Copyright (c) 2018 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
(https://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.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Definition of Terms . . . . . . . . . . . . . . . . . . . . . 4
3. Requirements Language . . . . . . . . . . . . . . . . . . . . 5
4. Reference Model . . . . . . . . . . . . . . . . . . . . . . . 6
5. General Procedures . . . . . . . . . . . . . . . . . . . . . 7
5.1. General Receiver-Site Procedures . . . . . . . . . . . . 8
5.1.1. Multicast Receiver Detection . . . . . . . . . . . . 8
5.1.2. Receiver-Site Registration . . . . . . . . . . . . . 9
5.1.3. Consolidation of the Replication List . . . . . . . . 10
5.2. General Source-Site Procedures . . . . . . . . . . . . . 10
5.2.1. Multicast Tree Building at the Source Site . . . . . 10
5.2.2. Multicast Destination Resolution . . . . . . . . . . 11
5.3. General LISP Notification Procedures . . . . . . . . . . 11
6. Source-Specific Multicast Trees . . . . . . . . . . . . . . . 12
6.1. Source Directly Connected to Source-ITRs . . . . . . . . 12
6.2. Source Not Directly Connected to Source-ITRs . . . . . . 12
7. Multihoming Considerations . . . . . . . . . . . . . . . . . 13
7.1. Multiple ITRs at a Source Site . . . . . . . . . . . . . 13
7.2. Multiple ETRs at a Receiver Site . . . . . . . . . . . . 13
7.3. Multiple RLOCs for an ETR at a Receiver Site . . . . . . 14
7.4. Multicast RLOCs for an ETR at a Receiver Site . . . . . . 14
8. PIM Any-Source Multicast Trees . . . . . . . . . . . . . . . 15
9. Signal-Free Multicast for Replication Engineering . . . . . . 16
10. Security Considerations . . . . . . . . . . . . . . . . . . . 18
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 19
12.1. Normative References . . . . . . . . . . . . . . . . . . 19
12.2. Informative References . . . . . . . . . . . . . . . . . 20
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21
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RFC 8378 Signal-Free LISP Multicast May 2018
1. Introduction
When multicast sources and receivers are active at LISP sites, and
the core network between the sites does not provide multicast
support, a signal-free mechanism can be used to create an overlay
that will allow multicast traffic to flow between sites and connect
the multicast trees at the different sites.
The signal-free mechanism proposed here does not extend PIM [RFC7761]
over the overlay as proposed in [RFC6831], nor does the mechanism
utilize direct signaling between the Receiver-ETRs and Sender-ITRs as
described in [LISP-MULTI-SIGNALING]. The signal-free mechanism
proposed reduces the amount of signaling required between sites to a
minimum and is centered around the registration of receiver sites for
a particular multicast group or multicast channel with the LISP
mapping system.
Registrations from the different receiver sites will be merged at the
mapping system to assemble a multicast-replication-list inclusive of
all Routing Locators (RLOCs) that lead to receivers for a particular
multicast group or multicast channel. The replication list for each
specific multicast entry is maintained as a database mapping entry in
the LISP mapping system.
When the Ingress Tunnel Router (ITR) at the source site receives
multicast traffic from sources at its site, the ITR can query the
mapping system by issuing Map-Request messages for the (S,G) source
and destination addresses in the packets received. The mapping
system will return the RLOC replication list to the ITR, which the
ITR will cache as per standard LISP procedure. Since the core is
assumed to not support multicast, the ITR will replicate the
multicast traffic for each RLOC on the replication list and will
unicast encapsulate the traffic to each RLOC. The combined function
or replicating and encapsulating the traffic to the RLOCs in the
replication list is referred to as "rep-encapsulation" in this
document.
The document describes general procedures (Section 5) and information
encoding that are required at the receiver sites and source sites to
achieve signal-free multicast interconnectivity. The general
procedures for mapping system notifications to different sites are
also described. A section dedicated to the specific case of Source-
Specific Multicast (SSM) trees discusses the implications to the
general procedures for SSM multicast trees over different topological
scenarios. A section on Any-Source Multicast (ASM) support is
included to identify the constraints that come along with supporting
it using LISP signal-free multicast.
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RFC 8378 Signal-Free LISP Multicast May 2018
There is a section dedicated to Replication Engineering, which is a
mechanism to reduce the impact of head-end replication. The mapping
system, via LISP signal-free mechanisms, can be used to build a layer
of Re-encapsulating Tunnel Routers (RTRs).
2. Definition of Terms
LISP-related terms, notably Map-Request, Map-Reply, Ingress Tunnel
Router (ITR), Egress Tunnel Router (ETR), Map-Server (MS), and
Map-Resolver (MR) are defined in the LISP specification [RFC6830].
Extensions to the definitions in [RFC6830] for their application to
multicast routing are documented in [RFC6831].
Terms defining interactions with the LISP mapping system are defined
in [RFC6833].
The following terms are consistent with the definitions in [RFC6830]
and [RFC6831]. The terms are specific cases of the general terms and
are defined here to facilitate the descriptions and discussions
within this particular document.
Source: Multicast source endpoint. The host that originates
multicast packets.
Receiver: Multicast group member endpoint. The host joins a
multicast group as a receiver of multicast packets sent to the group.
Receiver site: LISP site where multicast receivers are located.
Source site: LISP site where multicast sources are located.
RP site: LISP site where an ASM PIM Rendezvous Point (RP) [RFC7761]
is located. The RP site and the source site MAY be the same in some
situations.
Receiver-ETR: LISP decapsulating the Tunnel Router (xTR) at the
receiver site. This is a multicast ETR.
Source-ITR: LISP encapsulating xTR at the source site. This is a
multicast ITR.
RP-xTR: LISP xTR at the RP site. This is typically a multicast ITR.
Replication list: Mapping-entry containing the list of RLOCs that
have registered receivers for a particular multicast entry.
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RFC 8378 Signal-Free LISP Multicast May 2018
Multicast entry: A tuple identifying a multicast tree. Multicast
entries are in the form of (S-prefix, G-prefix).
Rep-encapsulation: The process of replicating and then encapsulating
traffic to multiple RLOCs.
Re-encapsulating Tunnel Router (RTR): An RTR is a router that
implements the re-encapsulating tunnel function detailed in Section 8
of the main LISP specification [RFC6830]. A LISP RTR performs packet
re-routing by chaining ETR and ITR functions, whereby it first
removes the LISP header of an ingress packet and then prepends a new
LISP header to an egress packet.
RTR Level: An RTR level is encoded in a Replication List Entry (RLE)
LISP Canonical Address Format (LCAF) Type detailed in [RFC8060].
Each entry in the replication list contains an address of an xTR and
a level value. Level values are used to create a replication
hierarchy so that ITRs at source LISP sites replicate to the lowest
(smaller value) level number RTRs in an RLE. And then RTRs at a
given level replicate to the next higher level of RTRs. The number
of RTRs at each level are engineered to control the fan-out or
replication factor, so a trade-off between the width of the level
versus the number of levels can be selected.
ASM: Any-Source Multicast as defined in [RFC3569] where multicast
distribution trees are built with a Rendezvous Point [RFC7761].
SSM: Source-Specific Multicast as defined in [RFC3569] where
multicast distribution trees are built and rooted at the multicast
router(s) directly connected to the multicast source.
3. Requirements Language
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 BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
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RFC 8378 Signal-Free LISP Multicast May 2018
4. Reference Model
The reference model that will be used for the discussion of the
signal-free multicast tree interconnection is illustrated in
Figure 1.
MS/MR
+---+
| |
+---+ +---+ +---+ +---+ +---+
Src-1 ----| R1|-----|ITR| | |ETR|------| R2|----- Rcv-2
+---+ +---+ | +---+ +---+
\ | /
Source-site-1 \ | / Receiver-site-2
\ | /
\ | /
\ | /
Core
/ \
/ \
/ \
/ \
/ \
+---+ +---+
Src-3 --------------|ITR| |ETR|---------------- Rcv-4
+---+ +---+
Source-site-3 Receiver-site-4
Figure 1: LISP Multicast Generic Reference Model
Sites 1 and 3 are source sites.
Source-site-3 presents a source (Src-3) that is directly connected to
the Source-ITR.
Source-site-1 presents a source (Src-1) that is one hop or more away
from the Source-ITR.
Receiver-site-2 and -4 are receiver sites with not-directly connected
and directly connected receiver endpoints, respectively.
R1 is a multicast router in Source-site-1.
R2 is a multicast router at the receiver site.
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RFC 8378 Signal-Free LISP Multicast May 2018
Map-Servers and Map-Resolvers are reachable in the RLOC space in the
core; only one is shown for illustration purposes, but these can be
many or even part of a distributed mapping system, such as a
Delegated Database Tree (DDT).
The procedures for interconnecting multicast trees over an overlay
can be broken down into three functional areas:
o Receiver-site procedures
o Source-site procedures
o LISP notification procedures
The receiver-site procedures will be common for most tree types and
topologies.
The procedures at the source site can vary depending on the type of
trees being interconnected as well as the topological relation
between sources and source-site xTRs. For ASM trees, a special case
of the source site is the RP site for which a variation of the
source-site procedures MAY be necessary if ASM trees are to be
supported in future specifications of LISP signal-free multicast.
The LISP notification procedures between sites are normalized for the
different possible scenarios. Certain scenarios MAY benefit from a
simplified notification mechanism or no notification requirement at
all.
5. General Procedures
The interconnection of multicast trees across different LISP sites
involves the following procedures to build the necessary multicast
distribution trees across sites.
1. The presence of multicast receiver endpoints is detected by the
Receiver-ETRs at the receiver sites.
2. Receiver-ETRs register their RLOCs as part of the replication
list for the multicast entry the detected receivers subscribe to.
3. The mapping system merges all Receiver-ETR or delivery-group
RLOCs to build a comprehensive replication list inclusive of all
receiver sites for each multicast entry.
4. LISP Map-Notify messages MUST be sent to the Source-ITR informing
of any changes in the replication list.
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RFC 8378 Signal-Free LISP Multicast May 2018
5. Multicast tree building at the source site is initiated when the
Source-ITR receives the LISP notification.
Once the multicast distribution trees are built, the following
forwarding procedures may take place:
1. The source sends multicast packets to the multicast group
destination address.
2. Multicast traffic follows the multicast tree built at the source
site and makes its way to the Source-ITRs.
3. The Source-ITR will issue a Map-Request to resolve the
replication list for the multicast entry.
4. The mapping system responds to the Source-ITR with a Map-Reply
containing the replication list for the multicast group
requested.
5. The Source-ITR caches the replication list received in the
map-reply for the multicast entry.
6. Multicast traffic is rep-encapsulated. That is, the packet is
replicated for each RLOC in the replication list and then
encapsulated to each one.
5.1. General Receiver-Site Procedures
5.1.1. Multicast Receiver Detection
When the Receiver-ETRs are directly connected to the receivers (e.g.,
Receiver-site-4 in Figure 1), the Receiver-ETRs will receive IGMP
reports from the receivers indicating which group the receivers wish
to subscribe to. Based on these IGMP reports, the Receiver-ETR is
made aware of the presence of receivers as well as which group they
are interested in.
When the Receiver-ETRs are several hops away from the receivers
(e.g., Receiver-site-2 in Figure 1), the Receiver-ETRs will receive
PIM join messages, which will allow the Receiver-ETR to know that
there are multicast receivers at the site and also to learn which
multicast group the receivers are for.
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RFC 8378 Signal-Free LISP Multicast May 2018
5.1.2. Receiver-Site Registration
Once the Receiver-ETRs detect the presence of receivers at the
receiver site, the Receiver-ETRs MUST issue Map-Register messages to
include the Receiver-ETR RLOCs in the replication list for the
multicast entry the receivers joined.
The Map-Register message MUST use the multicast entry (Source, Group)
tuple as its Endpoint ID (EID) record type with the Receiver-ETR
RLOCs conforming the locator set.
The EID in the Map-Register message MUST be encoded using the
Multicast Info LCAF Type defined in [RFC8060].
The RLOC in the Map-Register message MUST be encoded using the RLE
LCAF Type defined in [RFC8060] with the Level Value fields for all
entries set to 128 (decimal).
The encoding described above MUST be used consistently for Map-
Register messages, entries in the mapping system, Map-Reply messages,
as well as the map-cache at the Source-ITRs.
The Map-Register messages [RFC6830] sent by the Receiver-ETRs MUST
have the following bits set as specified here:
1. merge-request bit set to 1. The Map-Register messages are sent
with "Merge Semantics". The Map-Server will receive
registrations from a multitude of Receiver-ETRs. The Map-Server
will merge the registrations for common EIDs and maintain a
consolidated replication list for each multicast entry.
2. want-map-notify bit (M) set to 0. This tells the mapping system
that the Receiver-ETR does not expect to receive Map-Notify
messages as it does not need to be notified of all changes to the
replication list.
3. proxy-reply bit (P) set to 1. The merged replication list is
kept in the Map-Servers. By setting the proxy-reply bit, the
Receiver-ETRs instruct the mapping system to proxy reply to Map-
Requests issued for the multicast entries.
Map-Register messages for a particular multicast entry MAY be sent
for every receiver detected, even if previous receivers have been
detected for the particular multicast entry. This allows the
replication list to remain up to date.
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RFC 8378 Signal-Free LISP Multicast May 2018
Receiver-ETRs MUST be configured to know what Map-Servers Map-
Register messages are sent to. The configuration is likely to be
associated with an S-prefix that multiple (S,G) entries match to and
are more specific for. Therefore, the S-prefix determines the Map-
Server set in the least number of configuration statements.
5.1.3. Consolidation of the Replication List
The Map-Server will receive registrations from a multitude of
Receiver-ETRs. The Map-Server will merge the registrations for
common EIDs and consolidate a replication list for each multicast
entry.
When an ETR sends an RLE RLOC-record in a Map-Register and the RLE
already exists in the Map-Server's RLE-merged list, the Map-Server
will replace the single RLE with the information from the Map-
Register RLOC-record. The Map-Server MUST NOT merge duplicate RLOCs
in the consolidated replication list.
5.2. General Source-Site Procedures
Source-ITRs MUST register the unicast EIDs of any sources or
Rendezvous Points that may be present on the source site. In other
words, it is assumed that the sources and RPs are LISP EIDs.
The registration of the unicast EIDs for the sources or Rendezvous
Points allows the Map-Server to know where to send Map-Notify
messages to. Therefore, the Source-ITR MUST register the unicast
S-prefix EID with the want-map-notify bit set in order to receive
Map-Notify messages whenever there is a change in the replication
list.
5.2.1. Multicast Tree Building at the Source Site
When the source site receives the Map-Notify messages from the
mapping system as described in Section 5.3, it will initiate the
process of building a multicast distribution tree that will allow the
multicast packets from the source to reach the Source-ITR.
The Source-ITR MUST issue a PIM join for the multicast entry for
which it received the Map-Notify message. The join will be issued in
the direction of the source or in the direction of the RP for the SSM
and ASM cases, respectively.
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RFC 8378 Signal-Free LISP Multicast May 2018
5.2.2. Multicast Destination Resolution
On reception of multicast packets, the Source-ITR obtains the
replication list for the (S,G) addresses in the packets.
In order to obtain the replication list, the Source-ITR MUST issue a
Map-Request message in which the EID is the (S,G) multicast tuple,
which is encoded using the Multicast Info LCAF Type defined in
[RFC8060].
The mapping system (most likely the Map-Server) will Map-Reply with
the merged replication list maintained in the mapping system. The
Map-Reply message MUST follow the format defined in [RFC6830]; its
EID is encoded using the Multicast Info LCAF Type, and the
corresponding RLOC-records are encoded using the RLE LCAF Type. Both
LCAF Types are defined in [RFC8060].
5.3. General LISP Notification Procedures
The Map-Server will issue LISP Map-Notify messages to inform the
source site of the presence of receivers for a particular multicast
group over the overlay.
Updated Map-Notify messages SHOULD be issued every time a new
registration is received from a receiver site. This guarantees that
the source sites are aware of any potential changes in the multicast-
distribution-list membership.
The Map-Notify messages carry (S,G) multicast EIDs encoded using the
Multicast Info LCAF Type defined in [RFC8060].
Map-Notify messages will be sent by the Map-Server to the RLOCs with
which the unicast S-prefix EID was registered. In the case when
sources are discovered dynamically [LISP-EID-MOBILITY], xTRs MUST
register sources explicitly with the want-map-notify bit set. This
is so the ITR in the site the source has moved to can get the most
current replication list.
When both the receiver sites and the source sites register to the
same Map-Server, the Map-Server has all the necessary information to
send the Map-Notify messages to the source site.
When the Map-Servers are distributed (when using LISP-DDT [RFC8111]),
the receiver sites MAY register to one Map-Server while the source
site registers to a different Map-Server. In this scenario, the Map-
Server for the receiver sites MUST resolve the unicast S-prefix EID
across a distributed mapping transport system, per standard LISP
lookup procedures, and obtain the necessary information to send the
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RFC 8378 Signal-Free LISP Multicast May 2018
Map-Notify messages to the source site. The Map-Notify messages are
sent with an authentication length of 0 as they would not be
authenticated.
When the Map-Servers are distributed, different receiver sites MAY
register to different Map-Servers. However, this is not supported
with the currently defined mechanisms.
6. Source-Specific Multicast Trees
The interconnection of SSM trees across sites will follow the general
receiver-site procedures described in Section 5.1 on the receiver
sites.
The source-site procedures will vary depending on the topological
location of the source within the source site as described in
Sections 6.1 and 6.2 .
6.1. Source Directly Connected to Source-ITRs
When the source is directly connected to the Source-ITR, it is not
necessary to trigger signaling to build a local multicast tree at the
source site. Therefore Map-Notify messages are not required to
initiate building of the multicast tree at the source site.
Map-Notify messages are still required to ensure that any changes to
the replication list are communicated to the source site so that the
map-cache at the Source-ITRs is kept updated.
6.2. Source Not Directly Connected to Source-ITRs
The general LISP notification procedures described in Section 5.3
MUST be followed when the source is not directly connected to the
Source-ITR. On reception of Map-Notify messages, local multicast
signaling MUST be initiated at the source site per the general
source-site procedures for multicast tree building described in
Section 5.2.1.
In the SSM case, the IP address of the source is known, and it is
also registered with the LISP mapping system. Thus, the mapping
system MAY resolve the mapping for the source address in order to
send Map-Notify messages to the correct Source-ITR.
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RFC 8378 Signal-Free LISP Multicast May 2018
7. Multihoming Considerations
7.1. Multiple ITRs at a Source Site
When multiple ITRs exist at a source multicast site, care MUST be
taken that more than one ITR does not head-end replicate packets;
otherwise, receiver multicast sites will receive duplicate packets.
The following procedures will be used for each topology scenario:
o When more than one ITR is directly connected to the source host,
either the PIM DR or the IGMP querier (when PIM is not enabled on
the ITRs) is responsible for packet replication. All other ITRs
silently drop the packet. In the IGMP querier case, one or more
ITRs on the source LAN MUST be IGMP querier candidates.
Therefore, it is required that they be configured as such.
o When more than one ITR is multiple hops away from the source host
and one of the ITRs is the PIM Rendezvous Point, then the PIM RP
is responsible for packet replication.
o When more than one ITR is multiple hops away from the source host
and the PIM Rendezvous Point is not one of the ITRs, then one of
the ITRs MUST join to the RP. When a Map-Notify is received from
the Map-Server by an ITR, only the highest RLOC addressed ITR will
join toward the PIM RP or toward the source.
7.2. Multiple ETRs at a Receiver Site
When multiple ETRs exist in a receiver multicast site and each one
creates a multicast join state, each Map-Registers its RLOC address
to the mapping system. In this scenario, the replication happens on
the overlay causing multiple ETR entry points to replicate to all
receivers instead of a single ETR entry point replicating to all
receivers. If an ETR does not create join state, because it has not
received PIM joins or IGMP reports, it will not Map-Register its RLOC
addresses to the mapping system. The same procedures in Section 5.1
are followed.
When multiple ETRs exist on the same LAN as a receiver host, then the
PIM DR (when PIM is enabled) or the IGMP querier is responsible for
sending a Map-Register for its RLOC. In the IGMP case, one or more
ETRs on a LAN MUST be IGMP querier candidates. Therefore, it is
required that they are configured as such.
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RFC 8378 Signal-Free LISP Multicast May 2018
7.3. Multiple RLOCs for an ETR at a Receiver Site
It MAY be desirable to have multiple underlay paths to an ETR for
multicast packet delivery. This can be done by having multiple RLOCs
assigned to an ETR and having the ETR send Map-Registers for all its
RLOCs. By doing this, an ITR can choose a specific path based on
underlay performance and/or RLOC reachability.
It is recommended that an ETR send a Map-Register with a single RLOC-
record that uses the Explicit Locator Path (ELP) LCAF Type [RFC8060]
that is nested inside the RLE LCAF. For example, say ETR1 has
assigned RLOC1 and RLOC2 for a LISP receiver site. Also, there is
ETR2 in another LISP receiver site that has RLOC3. The two receiver
sites have the same (S,G) being joined. Here is how the RLOC-record
is encoded on each ETR:
ETR1: EID-record: (S,G)
RLOC-record: RLE[ ELP{ (RLOC1,s,p), (RLOC2,s,p) } ]
ETR2: EID-record: (S,G)
RLOC-record: RLE[ RLOC3 ]
And here is how the entry is merged and stored on the Map-Server
since the Map-Registers have an RLE-encoded RLOC-record:
MS: EID-record: (S,G)
RLOC-record: RLE[ RLOC3, ELP{ (RLOC1,s,p), (RLOC2,s,p) } ]
When the ITR receives a packet from a multicast source S for group G,
it uses the merged RLOC-record returned from the Map-Server. The ITR
replicates the packet to (RLOC3 and RLOC1) or (RLOC3 and RLOC2).
Since it is required for the s-bit to be set for RLOC1, the ITR MUST
replicate to RLOC1 if it is reachable. When the required p-bit is
also set, the RLOC-reachability mechanisms from [RFC6830] are
followed. If the ITR determines that RLOC1 is unreachable, it uses
RLOC2, as long as RLOC2 is reachable.
7.4. Multicast RLOCs for an ETR at a Receiver Site
This specification is focused on underlays without multicast support,
but it does not preclude the use of multicast RLOCs in RLEs. ETRs
MAY register multicast EID entries using multicast RLOCs. In such
cases, the ETRs will be joined to underlay multicast distribution
trees by using IGMP as a multicast host using mechanisms in [RFC2236]
and [RFC3376].
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8. PIM Any-Source Multicast Trees
LISP signal-free multicast can support ASM trees in limited but
acceptable topologies. It is suggested, for the simplification of
building ASM trees across the LISP overlay, to have PIM-ASM run
independently in each LISP site. What this means is that a PIM RP is
configured in each LISP site so PIM Register procedures and (*,G)
state maintenance is contained within the LISP site.
The following procedure will be used to support ASM in each LISP
site:
1. In a receiver site, the RP is co-located with the ETR. RPs for
different groups can be spread across each ETR, but is not
required.
2. When (*,G) state is created in an ETR, the procedures in
Section 5.1.2 are followed. In addition, the ETR registers
(S-prefix,G), where S-prefix is 0/0 (the respective unicast
default route for the address-family) to the mapping system.
3. In a source site, the RP is co-located with the ITR. RPs for
different groups can be spread across each ITR, but is not
required.
4. When a multicast source sends a packet, a PIM Register message is
delivered to the ITR, and the procedures in Section 5.2 are
followed.
5. When the ITR sends a Map-Request for (S,G) and no receiver site
has registered for (S,G), the mapping system will return the
(0/0,G) entry to the ITR so it has a replication list of all the
ETRs that have received (*,G) state.
6. The ITR stores the replication list in its map-cache for (S,G).
It replicates packets to all ETRs in the list.
7. ETRs decapsulate packets and forward based on (*,G) state in
their site.
8. When last-hop PIM routers join the newly discovered (S,G), the
ETR will store the state and follow the procedures in
Section 5.1.2.
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9. Signal-Free Multicast for Replication Engineering
The mechanisms in this specification can be applied to the "LISP
Replication Engineering" [LISP-RE] design. Rather than have the
layered LISP-RE RTR hierarchy use signaling mechanisms, the RTRs can
register their availability for multicast tree replication via the
mapping database system.
As stated in [LISP-RE], the RTR-layered hierarchy is used to avoid
head-end replication in replicating nodes closest to a multicast
source. Rather than have multicast ITRs replicate to each ETR in an
RLE of an (S,G) mapping database entry, it could replicate to one or
more layer 0 RTRs in the LISP-RE hierarchy.
This document specifies how the RTR hierarchy is determined but not
the optimal layers of RTRs to be used. Methods for determining
optimal paths or RTR topological closeness are out of scope for this
document.
There are two formats an (S,G) mapping database entry could have.
One format is a 'complete-format', and the other is a 'filtered-
format'. A 'complete-format' entails an (S,G) entry having multiple
RLOC-records that contain both ETRs that have registered as well as
the RTRs at the first level of the LISP-RE hierarchy for the ITR to
replicate to. When using 'complete-format', the ITR has the ability
to select if it replicates to RTRs or to the registered ETRs at the
receiver sites. A 'filtered-format' (S,G) entry is one where the
Map-Server returns the RLOC-records that it decides the ITR SHOULD
use. So replication policy is shifted from the ITRs to the mapping
system. The Map-Servers can also decide for a given ITR if it uses a
different set of replication targets per (S,G) entry for which the
ITR is replicating for.
The procedure for the LISP-RE RTRs to make themselves available for
replication can occur before or after any receivers join an (S,G)
entry or any sources send for a particular (S,G) entry. Therefore,
newly configured RTR state will be used to create new (S,G) state and
will be inherited into existing (S,G) state. A set of RTRs can
register themselves to the mapping system or a third party can do so
on their behalf. When RTR registration occurs, it is done with an
(S-prefix, G-prefix) entry so it can advertise its replication
services for a wide range of source/group combinations.
When a Map-Server receives (S,G) registrations from ETRs and
(S-prefix, G-prefix) registrations from RTRs, it has the option of
merging the RTR RLOC-records for each (S,G) that is more specific for
the (S-prefix, G-prefix) entry or keeping them separate. When
merging, a Map-Server is ready to return a 'complete-format' Map-
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Reply. When keeping the entries separate, the Map-Server can decide
what to include in a Map-Reply when a Map-Request is received. It
can include a combination of RLOC-records from each entry or decide
to use one or the other depending on policy configured.
+---+ +----+
Src-1 --------------|ITR| |ETR1|--------------- Rcv-1
+---+ +----+
\ /
Source-site-1 \ / Receiver-site-1
\ /
\ /
+----+ \ / +----+
|RTR1| \ / |RTR2| Level-0
+----+ \ / +----+
\ <^^^^^^^^^^^^^^> /
\ < > /
< Core Network >
< >
<vvvvvvvvvvvvvv>
/ / \ \
/ / \ \
+----+ / / \ \ +----+
|RTR3| / \ |RTR4| Level-1
+----+ / \ +----+
/ \
/ \
+----+ +----+
Rcv-2 --------------|ETR2| |ETR3|--------------- Rcv-3
+----+ +----+
Receiver-site-2 Receiver-site-3
Figure 2: LISP-RE Reference Model
Here is a specific example, illustrated in Figure 2, of (S,G) and
(S-prefix, G-prefix) mapping database entries when a source S is
behind an ITR, and there are receiver sites joined to (S,G) via ETR1,
ETR2, and ETR3. And there exists a LISP-RE hierarchy of RTR1 and
RTR2 at level-0 and RTR3 and RTR4 at level-1:
EID-record: (S,G)
RLOC-record: RLE: (ETR1, ETR2, ETR3), p1
EID-record: (S-prefix, G-prefix)
RLOC-record: RLE: (RTR1(L0), RTR2(L0), RTR3(L1), RTR4(L1)), p1
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The above entries are in the form in which they were registered and
are stored in a Map-Server. When a Map-Server uses 'complete-
format', the Map-Reply it originates has the mapping record encoded
as:
EID-record: (S,G)
RLOC-record: RLE: (RTR1(L0), RTR3(L1)), p1
RLOC-record: RLE: (ETR1, ETR2, ETR3), p1
The above Map-Reply allows the ITR to decide if it replicates to the
ETRs or if it SHOULD replicate only to level-0 RTR1. This decision
is left to the ITR since both RLOC-records have priority 1. If the
Map-Server wanted to force the ITR to replicate to RTR1, it would set
the ETRs RLOC-record to a priority greater than 1.
When a Map_server uses 'filtered-format', the Map-Reply it originates
has the mapping record encoded as:
EID-record: (S,G)
RLOC-record: RLE: (RTR1(L0), RTR3(L1)), p1
An (S,G) entry can contain alternate RTRs. So rather than
replicating to multiple RTRs, one RTR set MAY be used based on the
RTR reachability status. An ITR can test reachability status to any
layer 0 RTR using RLOC-probing, so it can choose one RTR from a set
to replicate to. When this is done, the RTRs are encoded in
different RLOC-records instead of together in one RLE RLOC-record.
This moves the replication load off the ITRs at the source site to
the RTRs inside the network infrastructure. This mechanism can also
be used by level-n RTRs to level-n+1 RTRs.
The following mapping would be encoded in a Map-Reply sent by a Map-
Server and stored in the ITR. The ITR would use RTR1 until it went
unreachable and then switch to use RTR2:
EID-record: (S,G)
RLOC-record: RTR1, p1
RLOC-record: RTR2, p2
10. Security Considerations
[LISP-SEC] defines a set of security mechanisms that provide origin
authentication, integrity, and anti-replay protection to LISP's EID-
to-RLOC mapping data conveyed via the mapping lookup process. LISP-
SEC also enables verification of authorization on EID-prefix claims
in Map-Reply messages.
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Additional security mechanisms to protect the LISP Map-Register
messages are defined in [RFC6833].
The security of the mapping system infrastructure depends on the
particular mapping database used. As an example, [RFC8111] defines a
public-key-based mechanism that provides origin authentication and
integrity protection to the LISP DDT protocol.
Map-Replies received by the Source-ITR can be signed (by the Map-
Server), so the ITR knows the replication list is from a legitimate
source.
Data-plane encryption can be used when doing unicast rep-
encapsulation as described in [RFC8061].
11. IANA Considerations
This document has no IANA actions.
12. References
12.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC2236] Fenner, W., "Internet Group Management Protocol, Version
2", RFC 2236, DOI 10.17487/RFC2236, November 1997,
<https://www.rfc-editor.org/info/rfc2236>.
[RFC3376] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.
Thyagarajan, "Internet Group Management Protocol, Version
3", RFC 3376, DOI 10.17487/RFC3376, October 2002,
<https://www.rfc-editor.org/info/rfc3376>.
[RFC3569] Bhattacharyya, S., Ed., "An Overview of Source-Specific
Multicast (SSM)", RFC 3569, DOI 10.17487/RFC3569, July
2003, <https://www.rfc-editor.org/info/rfc3569>.
[RFC6830] Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "The
Locator/ID Separation Protocol (LISP)", RFC 6830,
DOI 10.17487/RFC6830, January 2013,
<https://www.rfc-editor.org/info/rfc6830>.
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RFC 8378 Signal-Free LISP Multicast May 2018
[RFC6831] Farinacci, D., Meyer, D., Zwiebel, J., and S. Venaas, "The
Locator/ID Separation Protocol (LISP) for Multicast
Environments", RFC 6831, DOI 10.17487/RFC6831, January
2013, <https://www.rfc-editor.org/info/rfc6831>.
[RFC6833] Fuller, V. and D. Farinacci, "Locator/ID Separation
Protocol (LISP) Map-Server Interface", RFC 6833,
DOI 10.17487/RFC6833, January 2013,
<https://www.rfc-editor.org/info/rfc6833>.
[RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I.,
Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent
Multicast - Sparse Mode (PIM-SM): Protocol Specification
(Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March
2016, <https://www.rfc-editor.org/info/rfc7761>.
[RFC8060] Farinacci, D., Meyer, D., and J. Snijders, "LISP Canonical
Address Format (LCAF)", RFC 8060, DOI 10.17487/RFC8060,
February 2017, <https://www.rfc-editor.org/info/rfc8060>.
[RFC8111] Fuller, V., Lewis, D., Ermagan, V., Jain, A., and A.
Smirnov, "Locator/ID Separation Protocol Delegated
Database Tree (LISP-DDT)", RFC 8111, DOI 10.17487/RFC8111,
May 2017, <https://www.rfc-editor.org/info/rfc8111>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
12.2. Informative References
[LISP-EID-MOBILITY]
Portoles-Comeras, M., Ashtaputre, V., Moreno, V., Maino,
F., and D. Farinacci, "LISP L2/L3 EID Mobility Using a
Unified Control Plane", Work in Progress, draft-ietf-lisp-
eid-mobility-01, November 2017.
[LISP-MULTI-SIGNALING]
Farinacci, D. and M. Napierala, "LISP Control-Plane
Multicast Signaling", Work in Progress, draft-farinacci-
lisp-mr-signaling-06, February 2015.
[LISP-RE] Coras, F., Cabellos-Aparicio, A., Domingo-Pascual, J.,
Maino, F., and D. Farinacci, "LISP Replication
Engineering", Work in Progress, draft-coras-lisp-re-08,
November 2015.
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[LISP-SEC] Maino, F., Ermagan, V., Cabellos-Aparicio, A., and D.
Saucez, "LISP-Security (LISP-SEC)", Work in Progress,
draft-ietf-lisp-sec-15, April 2018.
[RFC8061] Farinacci, D. and B. Weis, "Locator/ID Separation Protocol
(LISP) Data-Plane Confidentiality", RFC 8061,
DOI 10.17487/RFC8061, February 2017,
<https://www.rfc-editor.org/info/rfc8061>.
Acknowledgements
The authors want to thank Greg Shepherd, Joel Halpern, and Sharon
Barkai for their insightful contribution to shaping the ideas in this
document. A special thanks to Luigi Iannone, LISP WG co-chair, for
shepherding this working group document. Thanks also goes to Jimmy
Kyriannis, Paul Vinciguerra, Florin Coras, and Yan Filyurin for
testing an implementation of this document.
Authors' Addresses
Victor Moreno
Cisco Systems
170 Tasman Drive
San Jose, California 95134
United States of America
Email: vimoreno@cisco.com
Dino Farinacci
lispers.net
San Jose, CA 95120
United States of America
Email: farinacci@gmail.com
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