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Internet Engineering Task Force (IETF) L. Iannone
Request for Comments: 9302 Huawei Technologies France
Obsoletes: 6834 D. Saucez
Category: Standards Track Inria
ISSN: 2070-1721 O. Bonaventure
Universite catholique de Louvain
October 2022
Locator/ID Separation Protocol (LISP) Map-Versioning
Abstract
This document describes the Locator/ID Separation Protocol (LISP)
Map-Versioning mechanism, which provides in-packet information about
Endpoint-ID-to-Routing-Locator (EID-to-RLOC) mappings used to
encapsulate LISP data packets. This approach is based on associating
a version number to EID-to-RLOC mappings and transporting such a
version number in the LISP-specific header of LISP-encapsulated
packets. LISP Map-Versioning is particularly useful to inform
communicating Ingress Tunnel Routers (ITRs) and Egress Tunnel Routers
(ETRs) about modifications of the mappings used to encapsulate
packets. The mechanism is optional and transparent to
implementations not supporting this feature, since in the LISP-
specific header and in the Map Records, bits used for Map-Versioning
can be safely ignored by ITRs and ETRs that do not support or do not
want to use the mechanism.
This document obsoletes RFC 6834, which is the initial experimental
specifications of the mechanisms updated by this document.
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 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/rfc9302.
Copyright Notice
Copyright (c) 2022 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 Revised BSD License text as described in Section 4.e of the
Trust Legal Provisions and are provided without warranty as described
in the Revised BSD License.
Table of Contents
1. Introduction
2. Requirements Notation
3. Definitions of Terms
4. LISP-Specific Header and Map-Version Numbers
5. Map Record and Map-Version
6. EID-to-RLOC Map-Version Number
6.1. The Null Map-Version
7. Dealing with Map-Version Numbers
7.1. Handling Dest Map-Version Number
7.2. Handling Source Map-Version Number
8. Security Considerations
9. Deployment Considerations
10. IANA Considerations
11. References
11.1. Normative References
11.2. Informative References
Appendix A. Benefits and Case Studies for Map-Versioning
A.1. Map-Versioning and Unidirectional Traffic
A.2. Map-Versioning and Interworking
A.2.1. Map-Versioning and Proxy-ITRs
A.2.2. Map-Versioning and LISP-NAT
A.2.3. Map-Versioning and Proxy-ETRs
A.3. RLOC Shutdown/Withdraw
Authors' Addresses
1. Introduction
This document describes the Map-Versioning mechanism used to provide
information on changes in the Endpoint-ID-to-Routing-Locator (EID-to-
RLOC) mappings used in the Locator/ID Separation Protocol (LISP)
[RFC9300] [RFC9301] context to perform packet encapsulation. The
mechanism is totally transparent to Ingress and Egress Tunnel Routers
(xTRs) not supporting or not using such functionality. The
architecture of LISP is described in [RFC9299]. The reader is
expected to be familiar with this introductory document.
This document obsoletes [RFC6834], which is the initial experimental
specification that describes the mechanisms updated by this document.
The basic mechanism is to associate a Map-Version number to each LISP
EID-to-RLOC mapping and transport such a version number in the LISP-
specific header. When a mapping changes, a new version number is
assigned to the updated mapping. A change in an EID-to-RLOC mapping
can be a modification in the RLOCs set, such as addition of, removal
of, or change in the priority or weight of one or more RLOCs.
When Map-Versioning is used, LISP-encapsulated data packets contain
the version number of the two mappings used to select the RLOCs in
the outer header (i.e., both source and destination RLOCs). This
information has two uses:
1. Map-Versioning enables the Egress Tunnel Router (ETR) receiving
the packet to know if the Ingress Tunnel Router (ITR) is using
the latest mapping version for the destination EID. If this is
not the case, the ETR can directly send a Map-Request containing
the updated mapping to the ITR to notify it of the latest
version. The ETR can also solicit the ITR to trigger a Map-
Request to obtain the latest mapping by sending a Solicit Map-
Request (SMR) message. Both options are defined in [RFC9301].
2. Map-Versioning enables an ETR receiving the packet to know if it
has in its EID-to-RLOC Map-Cache the latest mapping for the
source EID. If this is not the case, a Map-Request can be sent.
Considerations about the deployment of LISP Map-Versioning are
discussed in Section 9.
The benefits of Map-Versioning in some common LISP-related use cases
are discussed in Appendix A.
2. Requirements Notation
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.
3. Definitions of Terms
This document uses terms already defined in the main LISP
specifications ([RFC9300] and [RFC9301]). Here, we define the terms
that are specific to the Map-Versioning mechanism. Throughout the
whole document, big-endian bit ordering is used.
Map-Version number: An unsigned 12-bit integer is assigned to an
EID-to-RLOC mapping, indicating its version number (Section 6).
Null Map-Version: A Map-Version number with a value of 0x000 (zero),
which is used to signal that the Map-Version feature is not used
and no Map-Version number is assigned to the EID-to-RLOC mapping
(Section 6.1).
Dest Map-Version number: Map-Version of the mapping in the EID-to-
RLOC Map-Cache used by the ITR to select the RLOC present in the
'Destination Routing Locator' field of the outer IP header of LISP-
encapsulated packets (Section 7.1).
Source Map-Version number: Map-Version of the mapping in the EID-to-
RLOC Database used by the ITR to select the RLOC present in the
'Source Routing Locator' field of the outer IP header of LISP-
encapsulated packets (Section 7.2).
4. LISP-Specific Header and Map-Version Numbers
In order for the versioning approach to work, the LISP-specific
header has to carry both the Source Map-Version number and Dest Map-
Version number. This is done by setting the V-bit in the LISP-
specific header as specified in [RFC9300] and shown in the example in
Figure 1. All permissible combinations of the flags when the V-bit
is set to 1 are described in [RFC9300]. Not all of the LISP-
encapsulated packets need to carry version numbers. When the V-bit
is set, the LISP-specific header has the following encoding:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|N|L|E|V|I|R|K|K| Source Map-Version | Dest Map-Version |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Instance ID/Locator-Status-Bits |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: LISP-Specific Header Example When Map-Versioning Is in Use
Source Map-Version number (12 bits): See Section 3.
Dest Map-Version number (12 bits): See Section 3.
5. Map Record and Map-Version
To accommodate the mechanism, the Map Records that are transported in
Map-Request/Map-Reply/Map-Register messages need to carry the Map-
Version number as well. For reference, the Map Record (specified in
[RFC9301]) is reported here as an example in Figure 2. This memo
does not change the operation of Map-Request/Map-Reply/Map-Register
messages; they continue to be used as specified in [RFC9301].
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
+-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | Record TTL |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
R | Locator Count | EID mask-len | ACT |A| Reserved |
e +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
c | Rsvd | Map-Version Number | EID-Prefix-AFI |
o +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
r | EID-Prefix |
d +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| /| Priority | Weight | M Priority | M Weight |
| L +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| o | Unused Flags |L|p|R| Loc-AFI |
| c +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| \| Locator |
+-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Map-Record Format Example
Map-Version Number: Map-Version of the mapping contained in the
Record. As explained in Section 6.1, this field can be zero (0),
meaning that no Map-Version is associated to the mapping.
This packet format is backward compatible with xTRs that do not
support Map-Versioning, since they can simply ignore those bits.
A Map-Server receiving a message with an unexpected Map-Version
number, for instance an old one, MUST silently drop the message and
an appropriate log action SHOULD be taken.
6. EID-to-RLOC Map-Version Number
The EID-to-RLOC Map-Version number consists of an unsigned 12-bit
integer. The version number is assigned on a per-mapping basis,
meaning that different mappings have different version numbers, which
are updated independently. An update in the version number (i.e., a
newer version) MUST consist of an increment of the older version
number (the only exception is for the Null Map-Version as explained
in at the end of Section 6.1).
The space of version numbers has a circular order where half of the
version numbers are considered greater (i.e., newer) than the current
Map-Version number and the other half of the version numbers are
considered smaller (i.e., older) than the current Map-Version number.
This is basically a serial number on which the arithmetic described
in [RFC1982] applies. The ordering enables different reactions to
"older" and "newer" Map-Version numbers, whereby "older" numbers are
discarded and "newer" numbers trigger Map-Requests (see Section 7 for
further details). In a formal way, assuming that we have two version
numbers (V1 and V2), both different from the special value Null Map-
Version (see Section 6.1), and that the numbers are expressed on 12
bits, the following steps MUST be performed (in the same order shown
below) to strictly define their order:
1. V1 = V2 : The Map-Version numbers are the same.
2. V2 > V1 : if and only if
V2 > V1 AND (V2 - V1) <= 2^(12-1)
OR
V1 > V2 AND (V1 - V2) > 2^(12-1)
3. V1 > V2 : otherwise.
Using 12 bits and assuming a Map-Version value of 69, Map-Version
numbers in the range [70; 69 + 2048] are greater than 69, while Map-
Version numbers in the range [69 + 2049; (69 + 4095) mod 4096] are
smaller than 69.
The initial Map-Version number of a new EID-to-RLOC mapping SHOULD be
assigned randomly, but it MUST NOT be set to the Null Map-Version
value (0x000), because the Null Map-Version number has a special
meaning (see Section 6.1). Optionally, the initial Map-version
number may be configured.
Upon reboot, an ETR will use mappings configured in its EID-to-RLOC
Database. If those mappings have a Map-Version number, it will be
used according to the mechanisms described in this document. ETRs
MUST NOT automatically generate and assign Map-Version numbers to
mappings in the EID-to-RLOC Database.
6.1. The Null Map-Version
The value 0x000 (zero) is a special Map-Version number indicating
that there is actually no version number associated to the EID-to-
RLOC mapping. Such a value is used for special purposes and is named
the Null Map-Version number.
Map Records that have a Null Map-Version number indicate that there
is no Map-Version number associated with the mapping. This means
that LISP-encapsulated packets destined to the EID-Prefix referred to
by the Map Record MUST NOT contain any Map-Version numbers (V-bit set
to 0). If an ETR receives LISP-encapsulated packets with the V-bit
set, when the original mapping in the EID-to-RLOC Database has the
version number set to the Null Map-Version value, then those packets
MUST be silently dropped.
The Null Map-Version may appear in the LISP-specific header as a
Source Map-Version number (Section 7.2). When the Source Map-Version
number is set to the Null Map-Version value, it means that no map
version information is conveyed for the source site. This means that
if a mapping exists for the source EID in the EID-to-RLOC Map-Cache,
then the ETR MUST NOT compare the received Null Map-Version with the
content of the EID-to-RLOC Map-Cache (Section 7.2).
The fact that the 0 value has a special meaning for the Map-Version
number implies that, when updating a Map-Version number because of a
change in the mapping, if the next value is 0, then the Map-Version
number MUST be incremented by 2 (i.e., set to 1 (0x001), which is the
next valid value).
7. Dealing with Map-Version Numbers
The main idea of using Map-Version numbers is that whenever there is
a change in the mapping (e.g., adding/removing RLOCs, a change in the
weights due to Traffic Engineering policies, or a change in the
priorities) or a LISP site realizes that one or more of its own RLOCs
are no longer reachable from a local perspective (e.g., through IGP
or policy changes), the LISP site updates the mapping and also
assigns a new Map-Version number. Only the latest Map-Version number
has to be considered valid. Mapping updates and their corresponding
Map-Version Number must be managed so that a very old version number
will not be confused as a new version number (because of the circular
numbering space). To this end, simple measures can be taken, like
updating a mapping only when all active traffic is using the latest
version, or waiting a sufficient amount of time to be sure that the
mapping in LISP caches expires, which means waiting at least as long
as the mapping Time To Live (TTL) (as defined in [RFC9301]).
An ETR receiving a LISP packet with Map-Version numbers checks the
following predicates:
1. The ITR that has sent the packet has an up-to-date mapping in its
EID-to-RLOC Map-Cache for the destination EID and is performing
encapsulation correctly. See Section 7.1 for details.
2. In the case of bidirectional traffic, the mapping in the local
ETR EID-to-RLOC Map-Cache for the source EID is up to date. See
Section 7.2 for details.
7.1. Handling Dest Map-Version Number
When an ETR receives a packet, the Dest Map-Version number relates to
the mapping for the destination EID for which the ETR is an RLOC.
This mapping is part of the ETR EID-to-RLOC Database. Since the ETR
is authoritative for the mapping, it has the correct and up-to-date
Dest Map-Version number. A check on this version number MUST be
done, where the following cases can arise:
1. The packet arrives with the same Dest Map-Version number stored
in the EID-to-RLOC Database. This is the regular case. The ITR
sending the packet has, in its EID-to-RLOC Map-Cache, an up-to-
date mapping. No further actions are needed.
2. The packet arrives with a Dest Map-Version number newer (as
defined in Section 6) than the one stored in the EID-to-RLOC
Database. Since the ETR is authoritative on the mapping, meaning
that the Map-Version number of its mapping is the correct one,
the packet carries a version number that is not considered valid.
Therefore, the packet MUST be silently dropped and an appropriate
log action SHOULD be taken.
3. The packet arrives with a Dest Map-Version number older (as
defined in Section 6) than the one stored in the EID-to-RLOC
Database. This means that the ITR sending the packet has an old
mapping in its EID-to-RLOC Map-Cache containing stale
information. The ETR MAY choose to normally process the
encapsulated datagram according to [RFC9300]; however, the ITR
sending the packet MUST be informed that a newer mapping is
available, respecting rate-limitation policies described in
[RFC9301]. This is done with a Map-Request message sent back to
the ITR, as specified in [RFC9301]. One feature introduced by
Map-Version numbers is the possibility of blocking traffic not
using the latest mapping. This can happen if an ITR is not
updating the mapping for which the ETR is authoritative, or it
might be some form of attack. According to the rate-limitation
policy defined in [RFC9301] for Map-Request messages, after 10
retries, Map-Requests are sent every 30 seconds; if after the
first 10 retries the Dest Map-Version number in the packets is
not updated, the ETR SHOULD drop packets with a stale Map-Version
number. Operators can configure exceptions to this
recommendation, which are outside the scope of this document.
The rule in the third case MAY be more restrictive. If the Record
TTL of the previous mapping has already expired, all packets arriving
with an old Map-Version MUST be silently dropped right away without
issuing any Map-Request. Such action is permitted because, if the
new mapping with the updated version number has been unchanged for at
least the same amount of time as the Record TTL of the older mapping,
all the entries in the EID-to-RLOC Map-Caches of ITRs must have
expired. Indeed, all ITRs sending traffic should have refreshed the
mapping according to [RFC9301].
It is a protocol violation for LISP-encapsulated packets to contain a
Dest Map-Version number equal to the Null Map-Version number (see
Section 6.1).
7.2. Handling Source Map-Version Number
When an ETR receives a packet, the Source Map-Version number relates
to the mapping for the source EID for which the ITR that sent the
packet is authoritative. If the ETR has an entry in its EID-to-RLOC
Map-Cache for the source EID, then a check MUST be performed, and the
following cases can arise:
1. The packet arrives with the same Source Map-Version number as
that stored in the EID-to-RLOC Map-Cache. This is the regular
case. The ETR has in its EID-to-RLOC Map-Cache an up-to-date
copy of the mapping. No further actions are needed.
2. The packet arrives with a Source Map-Version number newer (as
defined in Section 6) than the one stored in the local EID-to-
RLOC Map-Cache. This means that the ETR has in its EID-to-RLOC
Map-Cache a mapping that is stale and needs to be updated. A
Map-Request MUST be sent to get the new mapping for the source
EID, respecting rate-limitation policies described in [RFC9301].
3. The packet arrives with a Source Map-Version number older (as
defined in Section 6) than the one stored in the local EID-to-
RLOC Map-Cache. Note that if the mapping is already present in
the EID-to-RLOC Map-Cache, this means that an explicit Map-
Request has been sent and a Map-Reply has been received from an
authoritative source. In this situation, the packet SHOULD be
silently dropped. Operators can configure exceptions to this
recommendation, which are outside the scope of this document.
If the ETR does not have an entry in the EID-to-RLOC Map-Cache for
the source EID, then the Source Map-Version number MUST be ignored.
See Appendix A.1 for an example of when this situation can arise.
8. Security Considerations
This document builds on the specification and operation of the LISP
control and data planes. The Security Considerations of [RFC9300]
and [RFC9301] apply. As such, Map-Versioning MUST NOT be used over
the public Internet and MUST only be used in trusted and closed
deployments. A thorough security analysis of LISP is documented in
[RFC7835].
Attackers can try to trigger a large number of Map-Requests by simply
forging packets with random Map-Versions. The Map-Requests are rate
limited as described in [RFC9301]. With Map-Versioning, it is
possible to filter packets carrying invalid version numbers before
triggering a Map-Request, thus helping to reduce the effects of DoS
attacks. However, it might not be enough to really protect against a
DDoS attack.
The present memo includes log action to be taken upon certain events.
It is recommended that implementations include mechanisms (which are
beyond the scope of this document) to avoid log resource exhaustion
attacks.
The specifications in the present memo are relatively conservative in
the sense that, in several cases, the packets are dropped. Such an
approach is the outcome of considerations made about the possible
risks that control plane actions that are triggered by the data plane
can be used to carry out attacks. There exists corner cases where,
even with an invalid Map-Version number, forwarding the packet might
be potentially considered safe; however, system manageability has
been given priority with respect to having to put in place more
machinery to be able to identify legitimate traffic.
9. Deployment Considerations
LISP requires multiple ETRs within the same site to provide identical
mappings for a given EID-Prefix. Map-Versioning does not require
additional synchronization mechanisms. Clearly, all the ETRs have to
reply with the same mapping, including the same Map-Version number;
otherwise, there can be an inconsistency that creates additional
control traffic, instabilities, and traffic disruptions.
There are two ways Map-Versioning is helpful with respect to
synchronization. On the one hand, assigning version numbers to
mappings helps in debugging, since quick checks on the consistency of
the mappings on different ETRs can be done by looking at the Map-
Version number. On the other hand, Map-Versioning can be used to
control the traffic toward ETRs that announce the latest mapping.
As an example, let's consider the topology of Figure 3 where ITR A.1
of Domain A is sending unidirectional traffic to Domain B, while A.2
of Domain A exchanges bidirectional traffic with Domain B. In
particular, ITR A.2 sends traffic to ETR B, and ETR A.2 receives
traffic from ITR B.
+-----------------+ +-----------------+
| Domain A | | Domain B |
| +---------+ | |
| | ITR A.1 |--- | |
| +---------+ \ +---------+ |
| | ------->| ETR B | |
| | ------->| | |
| +---------+ / | | |
| | ITR A.2 |--- -----| ITR B | |
| | | / +---------+ |
| | ETR A.2 |<----- | |
| +---------+ | |
| | | |
+-----------------+ +-----------------+
Figure 3: Example Topology
Obviously, in the case of Map-Versioning, both ITR A.1 and ITR A.2 of
Domain A must use the same value; otherwise, the ETR of Domain B will
start to send Map-Requests.
The same problem can, however, arise without Map-Versioning, for
instance, if the two ITRs of Domain A send different Locator-Status-
Bits. In this case, either the traffic is disrupted if ETR B does
not verify reachability or if ETR B will start sending Map-Requests
to confirm each change in reachability.
So far, LISP does not provide any specific synchronization mechanism
but assumes that synchronization is provided by configuring the
different xTRs consistently. The same applies for Map-Versioning.
If in the future any synchronization mechanism is provided, Map-
Versioning will take advantage of it automatically, since it is
included in the Map Record format, as described in Section 5.
10. IANA Considerations
This document has no IANA actions.
11. References
11.1. 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>.
[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>.
[RFC9300] Farinacci, D., Fuller, V., Meyer, D., Lewis, D., and A.
Cabellos, Ed., "The Locator/ID Separation Protocol
(LISP)", RFC 9300, DOI 10.17487/RFC9300, October 2022,
<https://www.rfc-editor.org/info/rfc9300>.
[RFC9301] Farinacci, D., Maino, F., Fuller, V., and A. Cabellos,
Ed., "Locator/ID Separation Protocol (LISP) Control
Plane", RFC 9301, DOI 10.17487/RFC9301, October 2022,
<https://www.rfc-editor.org/info/rfc9301>.
11.2. Informative References
[RFC1982] Elz, R. and R. Bush, "Serial Number Arithmetic", RFC 1982,
DOI 10.17487/RFC1982, August 1996,
<https://www.rfc-editor.org/info/rfc1982>.
[RFC6832] Lewis, D., Meyer, D., Farinacci, D., and V. Fuller,
"Interworking between Locator/ID Separation Protocol
(LISP) and Non-LISP Sites", RFC 6832,
DOI 10.17487/RFC6832, January 2013,
<https://www.rfc-editor.org/info/rfc6832>.
[RFC6834] Iannone, L., Saucez, D., and O. Bonaventure, "Locator/ID
Separation Protocol (LISP) Map-Versioning", RFC 6834,
DOI 10.17487/RFC6834, January 2013,
<https://www.rfc-editor.org/info/rfc6834>.
[RFC7835] Saucez, D., Iannone, L., and O. Bonaventure, "Locator/ID
Separation Protocol (LISP) Threat Analysis", RFC 7835,
DOI 10.17487/RFC7835, April 2016,
<https://www.rfc-editor.org/info/rfc7835>.
[RFC9299] Cabellos, A. and D. Saucez, Ed., "An Architectural
Introduction to the Locator/ID Separation Protocol
(LISP)", RFC 9299, DOI 10.17487/RFC9299, October 2022,
<https://www.rfc-editor.org/info/rfc9299>.
Appendix A. Benefits and Case Studies for Map-Versioning
In the following sections, we provide more discussion on various
aspects and uses of Map-Versioning. Security observations are
grouped in Section 8.
A.1. Map-Versioning and Unidirectional Traffic
When using Map-Versioning, the LISP-specific header carries two Map-
Version numbers for both source and destination mappings. This can
raise the question on what will happen in the case of unidirectional
flows, for instance, in the case presented in Figure 4, since the
LISP specifications do not mandate that the ETR have a mapping from
the source EID.
+-----------------+ +-----------------+
| Domain A | | Domain B |
| +---------+ +---------+ |
| | ITR A |----------->| ETR B | |
| +---------+ +---------+ |
| | | |
+-----------------+ +-----------------+
Figure 4: Unidirectional Traffic between LISP Domains
An ITR is able to put both the source and destination version numbers
in the LISP-specific header since the Source Map-Version number is in
its database, while the Dest Map-Version number is in its cache.
The ETR checks only the Dest Map-Version number, ignoring the Source
Map-Version number as specified in the final sentence of Section 7.2.
A.2. Map-Versioning and Interworking
Map-Versioning is compatible with the LISP interworking between LISP
and non-LISP sites as defined in [RFC6832]. LISP interworking
defines three techniques to allow communication LISP sites and non-
LISP sites, namely: Proxy-ITR, LISP-NAT, and Proxy-ETR. The
following text describes how Map-Versioning relates to these three
mechanisms.
A.2.1. Map-Versioning and Proxy-ITRs
The purpose of the Proxy-ITR (PITR) is to encapsulate traffic
originating in a non-LISP site in order to deliver the packet to one
of the ETRs of the LISP site (cf. Figure 5). This case is very
similar to the unidirectional traffic case described in Appendix A.1;
hence, similar rules apply.
+----------+ +-------------+
| LISP | | non-LISP |
| Domain A | | Domain B |
| +-------+ +-----------+ | |
| | ETR A |<-------| Proxy-ITR |<-------| |
| +-------+ +-----------+ | |
| | | |
+----------+ +-------------+
Figure 5: Unidirectional Traffic from Non-LISP Domain to LISP Domain
The main difference is that a Proxy-ITR does not have any mapping,
since it just encapsulates packets arriving from the non-LISP site,
and thus cannot provide a Source Map-Version. In this case, the
Proxy-ITR will just put the Null Map-Version value as the Source Map-
Version number, while the receiving ETR will ignore the field.
With this setup, LISP Domain A is able to check whether the PITR is
using the latest mapping. In the Dest Map-Version Number of the
LISP-specific header, the Proxy-ITR will put the version number of
the mapping it is using for encapsulation; the ETR A can use such
value as defined in Section 7.1.
A.2.2. Map-Versioning and LISP-NAT
The LISP-NAT mechanism is based on address translation from non-
routable EIDs to routable EIDs and does not involve any form of
encapsulation. As such, Map-Versioning does not apply in this case.
A.2.3. Map-Versioning and Proxy-ETRs
The purpose of the Proxy-ETR (PETR) is to decapsulate traffic
originating in a LISP site in order to deliver the packet to the non-
LISP site (cf. Figure 6). One of the main reasons to deploy PETRs
is to bypass Unicast Reverse Path Forwarding checks on the domain.
+----------+ +-------------+
| LISP | | non-LISP |
| Domain A | | Domain B |
| +-------+ +-----------+ | |
| | ITR A |------->| Proxy-ETR |------->| |
| +-------+ +-----------+ | |
| | | |
+----------+ +-------------+
Figure 6: Unidirectional Traffic from LISP Domain to Non-LISP Domain
A Proxy-ETR does not have any mapping, since it just decapsulates
packets arriving from the LISP site. In this case, the ITR can
interchangeably put a Map-Version value or the Null Map-Version value
as the Dest Map-Version number, since the receiving Proxy-ETR will
ignore the field.
With this setup, the Proxy-ETR, by looking at the Source Map-Version
Number, is able to check whether the mapping of the source EID has
changed. This is useful to perform source RLOC validation. In the
example above, traffic coming from the LISP domain has to be LISP
encapsulated with a source address being an RLOC of the domain. The
Proxy-ETR can retrieve the mapping associated to the LISP domain and
check if incoming LISP-encapsulated traffic is arriving from a valid
RLOC. A change in the RLOC-Set that can be used as source addresses
can be signaled via the version number, with the Proxy-ETR able to
request the latest mapping if necessary as described in Section 7.2.
A.3. RLOC Shutdown/Withdraw
Map-Versioning can also be used to perform a graceful shutdown or to
withdraw a specific RLOC. This is achieved by simply issuing a new
mapping, with an updated Map-Version number where the specific RLOC
to be shut down is withdrawn or announced as unreachable (via the
R-bit in the Map Record; see [RFC9301]) but without actually turning
it off.
Upon updating the mapping, the RLOC will receive less and less
traffic because remote LISP sites will request the updated mapping
and see that it is disabled. At least one TTL, plus a little time
for traffic transit, after the mapping is updated, it should be safe
to shut down the RLOC gracefully, because all sites actively using
the mapping should have been updated.
Note that a change in ETR for a flow can result in the reordering of
the packet in the flow just as any other routing change could cause
reordering.
Authors' Addresses
Luigi Iannone
Huawei Technologies France
Email: luigi.iannone@huawei.com
Damien Saucez
Inria
2004 route des Lucioles - BP 93
Sophia Antipolis
France
Email: damien.saucez@inria.fr
Olivier Bonaventure
Universite catholique de Louvain
Email: olivier.bonaventure@uclouvain.be