LISP Traffic Engineering
draft-ietf-lisp-te-21
| Document | Type | Active Internet-Draft (lisp WG) | |
|---|---|---|---|
| Authors | Dino Farinacci , Michael Kowal , Parantap Lahiri , Padma Pillay-Esnault | ||
| Last updated | 2025-06-13 (Latest revision 2025-05-13) | ||
| Replaces | draft-farinacci-lisp-te | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | Experimental | ||
| Formats | |||
| Reviews |
OPSDIR IETF Last Call review
by Dhruv Dhody
Has issues
GENART IETF Last Call review
by Peter Yee
Ready w/issues
SECDIR IETF Last Call Review due 2025-06-04
Incomplete
|
||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | Submitted to IESG for Publication | |
| Document shepherd | Padma Pillay-Esnault | ||
| Shepherd write-up | Show Last changed 2025-02-04 | ||
| IESG | IESG state | IESG Evaluation | |
| Action Holder |
Jim Guichard
24
|
||
| Consensus boilerplate | Yes | ||
| Telechat date |
On agenda of 2025-07-10 IESG telechat
Has 2 DISCUSSes. Has enough positions to pass once DISCUSS positions are resolved. |
||
| Responsible AD | Jim Guichard | ||
| Send notices to | padma.ietf@gmail.com | ||
| IANA | IANA review state | IANA OK - No Actions Needed |
draft-ietf-lisp-te-21
LISP Working Group D. Farinacci
Internet-Draft lispers.net
Intended status: Experimental M. Kowal
Expires: 14 November 2025 cisco Systems
P. Lahiri
Ebay
P. Pillay-Esnault, Ed.
Independent
13 May 2025
LISP Traffic Engineering
draft-ietf-lisp-te-21
Abstract
This document describes how LISP re-encapsulating tunnels can be used
for Traffic Engineering purposes. The mechanisms described in this
document require no LISP protocol changes but do introduce a new
locator (RLOC) encoding. The Traffic Engineering features provided
by these LISP mechanisms can span intra-domain, inter-domain, or a
combination of both.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 14 November 2025.
Copyright Notice
Copyright (c) 2025 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.
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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. Requirements Language . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Definition of Terms . . . . . . . . . . . . . . . . . . . . . 3
4. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 4
5. Explicit Locator Paths . . . . . . . . . . . . . . . . . . . 6
5.1. ELP Re-optimization . . . . . . . . . . . . . . . . . . . 8
5.2. Using Recursion . . . . . . . . . . . . . . . . . . . . . 8
5.3. ELP Selection based on Class of Service . . . . . . . . . 9
5.4. Packet Loop Avoidance . . . . . . . . . . . . . . . . . . 10
6. RLOC Probing by RTRs . . . . . . . . . . . . . . . . . . . . 11
7. ELP Probing . . . . . . . . . . . . . . . . . . . . . . . . . 11
8. Service Chaining . . . . . . . . . . . . . . . . . . . . . . 11
9. Interworking Considerations . . . . . . . . . . . . . . . . . 12
10. Multicast Considerations . . . . . . . . . . . . . . . . . . 13
11. Security Considerations . . . . . . . . . . . . . . . . . . . 15
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 15
13.1. Normative References . . . . . . . . . . . . . . . . . . 15
13.2. Informative References . . . . . . . . . . . . . . . . . 16
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . 16
Appendix B. Document Change Log . . . . . . . . . . . . . . . . 16
B.1. Changes to draft-ietf-lisp-te-21 . . . . . . . . . . . . 16
B.2. Changes to draft-ietf-lisp-te-20 . . . . . . . . . . . . 16
B.3. Changes to draft-ietf-lisp-te-19 . . . . . . . . . . . . 17
B.4. Changes to draft-ietf-lisp-te-18 . . . . . . . . . . . . 17
B.5. Changes to draft-ietf-lisp-te-17 . . . . . . . . . . . . 17
B.6. Changes to draft-ietf-lisp-te-16 . . . . . . . . . . . . 17
B.7. Changes to draft-ietf-lisp-te-15 . . . . . . . . . . . . 17
B.8. Changes to draft-ietf-lisp-te-14 . . . . . . . . . . . . 17
B.9. Changes to draft-ietf-lisp-te-13 . . . . . . . . . . . . 17
B.10. Changes to draft-ietf-lisp-te-12 . . . . . . . . . . . . 18
B.11. Changes to draft-ietf-lisp-te-11 . . . . . . . . . . . . 18
B.12. Changes to draft-ietf-lisp-te-10 . . . . . . . . . . . . 18
B.13. Changes to draft-ietf-lisp-te-09 . . . . . . . . . . . . 18
B.14. Changes to draft-ietf-lisp-te-08 . . . . . . . . . . . . 18
B.15. Changes to draft-ietf-lisp-te-07 . . . . . . . . . . . . 18
B.16. Changes to draft-ietf-lisp-te-06 . . . . . . . . . . . . 18
B.17. Changes to draft-ietf-lisp-te-05 . . . . . . . . . . . . 18
B.18. Changes to draft-ietf-lisp-te-04 . . . . . . . . . . . . 19
B.19. Changes to draft-ietf-lisp-te-03 . . . . . . . . . . . . 19
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B.20. Changes to draft-ietf-lisp-te-02 . . . . . . . . . . . . 19
B.21. Changes to draft-ietf-lisp-te-01 . . . . . . . . . . . . 19
B.22. Changes to draft-ietf-lisp-te-00 . . . . . . . . . . . . 19
B.23. Changes to draft-farinacci-lisp-te-02 through -12 . . . . 19
B.24. Changes to draft-farinacci-lisp-te-01.txt . . . . . . . . 19
B.25. Changes to draft-farinacci-lisp-te-00.txt . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20
1. 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.
2. Introduction
This document describes extensions to the Locator/Identifier
Separation Protocol (LISP) for traffic engineering features.
When LISP routers encapsulate packets to other LISP routers, the path
stretch is typically 1, meaning the packet travels on the shortest
path from the encapsulating ITR to the decapsulating ETR at the
destination site. The direct path is determined by the underlying
routing protocol and metrics it uses to find the shortest path.
This specification will examine how re-encapsulating tunnels
[RFC9300] can be used so a packet can take an administratively
specified path, a congestion avoidance path, a failure recovery path,
or multiple load-shared paths, as it travels from ITR to ETR. By
introducing an Explicit Locator Path (ELP) locator encoding
[RFC8060], an ITR can encapsulate a packet to a Re-Encapsulating
Tunnel Router (RTR) which decapsulates the packet, then encapsulates
it to the next locator in the ELP.
3. Definition of Terms
Refer to [RFC9300] for authoritative definitions for terms EID, RLOC,
RTR, and Recursive Tunneling. The other terms defined in this
section add to the canonical definition to reflect the design
considerations in this specification.
Explicit Locator Path (ELP): The ELP is an explicit list of RLOCs
for each RTR a packet SHOULD travel along its path toward a final
destination ETR (or PETR). The list MAY be a strict ordering
where each RLOC in the list is visited. However, the path from
one RTR to another is determined by the underlying routing
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protocol and how the infrastructure assigns metrics and policies
for the path. The definition of an ELP is found in section 3 of
[RFC8060].
Re-Encapsulating Tunnel Router (RTR): An RTR as defined in [RFC9300]
acts as an ITR (or PITR) by making a decision where to encapsulate
the packet based on the next locator in the ELP towards the final
destination ETR.
4. Overview
Typically, a packet's path from source EID to destination EID travels
through the locator core via the encapsulating ITR directly to the
decapsulating ETR as the following diagram illustrates:
Legend:
seid: Packet is originated by source EID 'seid'.
deid: Packet is consumed by destination EID 'deid'.
A, B, C, D : Core routers in different ASes.
---> : The physical underlay topology supported by routing
protocols.
===> : A multi-hop underlay path to realize a LISP tunnel between
LISP routers.
In Figure 1 below, the encapsulation tunnel path between ITR and ETR
is realized by underlay routers (A, B, C, D) so packets can be
delivered which are sent by EID seid to destination EID deid.
Core Network
Source site (----------------------------) Destination Site
+--------+ ( ) +---------+
| \ ( ) / |
| seid ITR ---(---> A --> B --> C --> D ---)---> ETR deid |
| / || ( ) ^^ \ |
+--------+ || ( ) || +---------+
|| (----------------------------) ||
|| ||
===========================================
LISP Tunnel
Figure 1: Typical Data Path from ITR to ETR
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In Figure 2, we introduce RTRs 'X' and 'Y' which creates the
opportunity for a tunnel encapsulation path between LISP routers X
and Y. For packets encapsulated by ITR to ETR, it may be desirable
to route around the link B-->C, one could provide an ELP of (X,Y,etr)
to achieve this:
Core Network
Source site (----------------------------) Destination Site
+--------+ ( ) +---------+
| \ ( ) / |
| seid ITR ---(---> A --> B --> C --> D ---)---> ETR deid |
| / || ( / ^ ) ^^ \ |
| / || ( | \ ) || \ |
+-------+ || ( v | ) || +--------+
|| ( X ======> Y ) ||
|| ( ^^ || ) ||
|| (--------||---------||-------) ||
|| || || ||
================= =================
LISP Tunnel LISP Tunnel
Figure 2: ELP tunnel path ITR ==> X, then X ==> Y, and then Y ==> ETR
In this case, the LISP router ITR encapsulates to X, and then X re-
encapsulates to Y, and then finally Y re-encapsulates to ETR.
There are various reasons why the path from 'seid' to 'deid' may want
to avoid the path from B to C. To list a few:
* There may not be sufficient capacity provided by the networks that
connect B and C together.
* There may be a policy reason to avoid the ASes that make up the
path between B and C.
* There may be a failure on the path between B and C which makes the
path unreliable.
* There may be monitoring or traffic inspection resources close to
RTRs X and Y that do network accounting or measurement.
* There may be a chain of services performed at RTRs X and Y
regardless if the path from ITR to ETR is through B and C.
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5. Explicit Locator Paths
The notation for a general formatted ELP is (x, y, etr), see
[RFC8060] for packet format details, represents the list of RTRs a
packet can travel through to reach the final tunnel hop to the ETR.
The procedure for using an ELP at each tunnel hop is as follows:
1. The ITR will retrieve the ELP from the mapping database. If no
ELP is returned from the mapping system, follow typical
procedures from [RFC9301]. When an ELP is returned, an ELP
validity check MUST be performed as detailed in Section 5.4.
2. The ITR will encapsulate the packet to RLOC 'x'. If the S-bit is
not set in the ELP, then the ITR MAY encapsulate to subsequent
xTRs in the ELP list. Otherwise, when the S-bit is set and an
xTR determines the RLOC is not reachable, it MUST NOT use any of
the remaining entries in the ELP list and drop the packet. If
the L-bit is set, then the ITR does a mapping system lookup on
EID 'x' to obtain an RLOC, call it x', which it then encapsulates
to.
3. The RTR with RLOC 'x' will decapsulate the packet. It will use
the decapsulated packet's destination address as a lookup into
the mapping database to retrieve the ELP.
4. RTR 'x' will encapsulate the packet to RTR with RLOC 'y'.
5. The RTR with RLOC 'y' will decapsulate the packet. It will use
the decapsulated packet's destination address as a lookup into
the mapping database to retrieve the ELP.
6. RTR 'y' will encapsulate the packet on the final tunnel hop to
ETR with RLOC 'etr'.
7. The ETR will decapsulate the packet and deliver the packet to the
EID inside of its site.
The specific encoding format for the ELP can be found in [RFC8060].
It is defined that an ELP will appear as a single encoded locator in
a locator-set. Say for instance, we have a mapping entry for EID-
prefix 192.0.2.0/24 (or if ipv6 2001:db8:200::/48) that is reachable
via 4 locators. Two locators are being used as active/active and the
other two are used as active/active if the first two go unreachable
(as noted by the priority assignments below). This is what the
mapping entry would look like:
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EID-prefix: 192.0.2.0/24
Locator-set: ETR-A: priority 1, weight 50
ETR-B: priority 1, weight 50
ETR-C: priority 2, weight 50
ETR-D: priority 2, weight 50
EID-prefix: 2001:db8:200::/48
Locator-set: ETR-A: priority 1, weight 50
ETR-B: priority 1, weight 50
ETR-C: priority 2, weight 50
ETR-D: priority 2, weight 50
If an ELP is going to be used to have a policy path to ETR-A and
possibly another policy path to ETR-B, the locator-set would be
encoded as follows (for each example ELP entry within an RLOC-record
below, S-bit=1, L-bit=0, P-bit=0):
EID-prefix: 192.0.2.0/24
Locator-set: (x, y, ETR-A): priority 1, weight 50
(q, r, ETR-B): priority 1, weight 50
ETR-C: priority 2, weight 50
ETR-D: priority 2, weight 50
EID-prefix: 2001:db8:200::/48
Locator-set: (x, y, ETR-A): priority 1, weight 50
(q, r, ETR-B): priority 1, weight 50
ETR-C: priority 2, weight 50
ETR-D: priority 2, weight 50
The mapping entry with ELP locators is registered to the mapping
database system, see [RFC9301] for details, just like any other
mapping entry would. The registration is typically performed by the
ETR(s) that are assigned and own the EID-prefix. That is, the
destination site makes the choice of the RTRs in the ELP.
Alternatively, it may be common practice for a third-party system
(not an ETR network entity) to register ELP mappings. This can be
done via a general purpose SDN provisioning system, for example.
Another case where a locator-set can be used for flow-based load-
sharing across multiple paths to the same destination site:
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EID-prefix: 192.0.2.0/24
Locator-set: (x, y, ETR-A): priority 1, weight 75
(q, r, ETR-A): priority 1, weight 25
EID-prefix: 2001:db8:200::/48
Locator-set: (x, y, ETR-A): priority 1, weight 75
(q, r, ETR-A): priority 1, weight 25
Using this mapping entry, an ITR would load split 75% of the EID
flows on the (x, y, ETR-A) ELP path and 25% of the EID flows on the
(q, r, ETR-A) ELP path. If any of the ELPs go down, then the other
can take 100% of the load. For mapping system lookups and map-cache
management, see [RFC9300] for details.
5.1. ELP Re-optimization
ELP re-optimization is a process of changing the RLOCs of an ELP due
to underlying network change conditions. Just like when there is any
locator change for a locator-set, the procedures from the main LISP
specification [RFC9300] are followed.
When a RLOC from an ELP is changed, Map-Notify messages [RFC9301] can
be used to inform the existing RTRs in the ELP so they can do a
lookup to obtain the latest version of the ELP. Map-Notify messages
can also be sent to new RTRs in an ELP so they can get the ELP in
advance to receiving packets that will use the ELP. This can
minimize packet loss during mapping database lookups in RTRs.
5.2. Using Recursion
In the previous examples, we showed how an ITR encapsulates using an
ELP of (x, y, etr). When a packet is encapsulated by the ITR to RTR
'x', the RTR may want a policy path to RTR 'y' and run another level
of re-encapsulating tunnels for packets destined to RTR 'y'. In this
case, the L-bit is set to 1, RTR 'x' does not encapsulate packets to
'y' but rather performs a mapping database lookup on the address 'y',
which returns a ELP-based locator record for a path to RTR 'y', and
encapsulates packets to the first-hop of the returned ELP. If the
ELP path to RTR 'y' is an internal path within a LISP site, the
lookup for RTR 'y' can be done to a private mapping system. The
decision to use address 'y' as an encapsulation address versus a
lookup address is based on the L-bit setting for 'y' in the ELP
entry. The decision and policy of ELP encodings are local to the
entity which registers the EID-prefix associated with the ELP.
Another example of recursion is when the ITR uses the ELP (x, y, etr)
to first prepend a header with a destination RLOC of the ETR and then
prepend another header and encapsulate the packet to RTR 'x'. When
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RTR 'x' decapsulates the packet, rather than doing a mapping database
lookup on RTR 'y' the last example showed, instead RTR 'x' does a
mapping database lookup on ETR 'etr'. In this scenario, RTR 'x' can
choose an ELP from the locator-set by considering the source RLOC
address of the ITR versus considering the source EID.
This additional level of recursion also brings advantages for the
provider of RTR 'x' to store less state. Since RTR 'x' does not need
to look at the inner most header, it does not need to store EID
state. It only stores an entry for RTR 'y' which many EID flows
could share for scaling benefits. The locator-set for entry 'y'
could either be a list of typical locators, a list of ELPs, or
combination of both. Another advantage is that packet load-splitting
can be accomplished by examining the source of a packet. If the
source is an ITR versus the source being the last-hop of an ELP the
last-hop selected, different forwarding paths can be used.
5.3. ELP Selection based on Class of Service
Paths to an ETR may want to be selected based on different classes of
service. Packets from a set of sources that have premium service can
use ELP paths that are less congested where normal sources use ELP
paths that compete for less resources or use longer paths for best
effort service.
Using source/destination lookups into the mapping database can yield
different ELPs. For example, a premium service flow with
(source=198.51.100.1, dest=192.0.2.1) or for ipv6
(source=2001:db8:100::1, dest=2001:db8:200::1) can be described by
using the following mapping entry:
EID-prefix: (198.51.100.0/24, 192.0.2.0/24)
Locator-set: (x, y, ETR-A): priority 1, weight 50
(q, r, ETR-A): priority 1, weight 50
EID-prefix: (2001:db8:100::/48, 2001:db8:200::/48)
Locator-set: (x, y, ETR-A): priority 1, weight 50
(q, r, ETR-A): priority 1, weight 50
And all other best-effort sources would use different mapping entry
described by:
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EID-prefix: (0.0.0.0/0, 192.0.2.0/24)
Locator-set: (x, x', y, y', ETR-A): priority 1, weight 50
(q, q', r, r', ETR-A): priority 1, weight 50
EID-prefix: (::/0, 2001:db8:200::/48)
Locator-set: (x, x', y, y', ETR-A): priority 1, weight 50
(q, q', r, r', ETR-A): priority 1, weight 50
If the source/destination lookup is coupled with recursive lookups,
then an ITR can encapsulate to the ETR, prepending a header that
selects source address ITR-1 based on the premium class of service
source, or selects source address ITR-2 for best-effort sources with
normal class of service. The ITR then does another lookup in the
mapping database on the prepended header using lookup key
(source=ITR-1, dest= 192.0.2.1) or for ipv6 (source=ITR-1,
dest=2001:db8:200::1)that returns the following mapping entry:
EID-prefix: (ITR-1, 192.0.2.0/24)
Locator-set: (x, y, ETR-A): priority 1, weight 50
(q, r, ETR-A): priority 1, weight 50
EID-prefix: (ITR-1, 2001:db8:200::/48)
Locator-set: (x, y, ETR-A): priority 1, weight 50
(q, r, ETR-A): priority 1, weight 50
And all other sources would use different mapping entry with a lookup
key of (source=ITR-2, dest= 192.0.2.1) or for ipv6 (source=ITR-2,
dest=2001:db8:200::1) :
EID-prefix: (ITR-2, 192.0.2.0/24)
Locator-set: (x, x', y, y', ETR-A): priority 1, weight 50
(q, q', r, r', ETR-A): priority 1, weight 50
EID-prefix: (ITR-2, 2001:db8:200::/48)
Locator-set: (x, x', y, y', ETR-A): priority 1, weight 50
(q, q', r, r', ETR-A): priority 1, weight 50
This will scale the mapping system better by having fewer source/
destination combinations. Refer to the Source/Dest LCAF type
described in [RFC8060] for encoding EIDs in Map-Request and Map-
Register messages.
5.4. Packet Loop Avoidance
An ELP that is first used by an ITR MUST be inspected for encoding
loops. If any RLOC appears twice in the ELP, it MUST NOT be used.
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Since it is expected that multiple mapping systems will be used,
there can be a loop across ELPs when registered in different mapping
systems. The TTL copying procedures for re-encapsulating tunnels and
recursive tunnels in [RFC9300] MUST be followed.
6. RLOC Probing by RTRs
Since an RTR knows the next tunnel hop to encapsulate to, it can
monitor the reachability of the next-hop RTR. As long as the next-
hop RTR sets the P-bit in the ELP list entry, the RTR can use RLOC-
probing according to the procedures in [RFC9301]. When the RLOC is
determined unreachable by the RLOC-probing mechanisms, the RTR can
use another locator in the locator-set. That could be the final ETR,
a RLOC of another RTR, or an ELP where it MUST search for itself and
use the next RLOC in the ELP list to encapsulate to.
RLOC-probing can also be used to measure delay on the path between
RTRs and when it is desirable switch to another lower delay ELP.
7. ELP Probing
Since an ELP-node knows the reachability of the next ELP-node in a
ELP by using RLOC probing, the sum of reachability can determine the
reachability of the entire path. A head-end ITR/RTR/PITR can
determine the quality of a path and decide to select one path from
another based on the telemetry data gathered by RLOC-probing for each
encapsulation hop.
ELP-probing mechanism details can be found in
[I-D.filyurin-lisp-elp-probing].
8. Service Chaining
An ELP can be used to deploy services at each re-encapsulation point
in the network. One example is to implement a honey-pot service when
a destination EID is being DoS attacked. That is, when a DoS attack
is recognized when the encapsulation path is between ITR and ETR, an
ELP can be registered for a destination EID to the mapping database
system. The ELP can include an RTR so the ITR can encapsulate
packets to the RTR which will decapsulate and deliver packets to a
scrubber service device. The scrubber could decide if the offending
packets are dropped or allowed to be sent to the destination EID. In
which case, the scrubber delivers packets back to the RTR which
encapsulates to the ETR.
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9. Interworking Considerations
[RFC6832] defines procedures for how non-LISP sites talk to LISP
sites. The network elements defined in the Interworking
specification, the proxy ITR (PITR) and proxy ETR (PETR) (as well as
their multicast counterparts defined in [RFC6831]) can participate in
LISP-TE. That is, a PITR and a PETR can appear in an ELP list and
act as an RTR.
Note when an RLOC appears in an ELP, it can be of any address-family.
There can be a mix of IPv4 and IPv6 locators present in the same ELP.
This can provide benefits where islands of one address-family or the
other are supported and connectivity across them is necessary. For
instance, an ELP can look like:
(x4, a46, b64, y4, etr)
Where an IPv4 ITR will encapsulate using an IPv4 RLOC 'x4' and 'x4'
could reach an IPv4 RLOC 'a46', but RTR 'a46' encapsulates to an IPv6
RLOC 'b64' when the network between them is IPv6-only. Then RTR
'b64' encapsulates to IPv4 RLOC 'y4' if the network between them is
dual-stack.
Note that RTRs can be used for NAT-traversal scenarios
[I-D.ermagan-lisp-nat-traversal] as well to reduce the state in both
an xTR that resides behind a NAT and the state the NAT needs to
maintain. In this case, the xTR only needs a default map-cache entry
pointing to the RTR for outbound traffic and all remote ITRs can
reach EIDs through the xTR behind a NAT via a single RTR (or a small
set RTRs for redundancy).
RTRs have some scaling features to reduce the number of locator-set
changes, the amount of state, and control packet overhead:
* When ITRs and PITRs are using a small set of RTRs for
encapsulating to "orders of magnitude" more EID-prefixes, the
probability of locator-set changes are limited to the RTR RLOC
changes versus the RLOC changes for the ETRs associated with the
EID-prefixes if the ITRs and PITRs were directly encapsulating to
the ETRs. This comes at an expense in packet stretch, but
depending on RTR placement, this expense can be mitigated.
* When RTRs are on-path between many pairwise EID flows, ITRs and
PITRs can store a small number of coarse EID-prefixes.
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* RTRs can be used to help scale RLOC-probing. Instead of ITRs
RLOC-probing all ETRs for each destination site it has cached, the
ITRs can probe a smaller set of RTRs which in turn, probe the
destination sites.
10. Multicast Considerations
ELPs have application in multicast environments. Just like RTRs can
be used to provide connectivity across different address family
islands, RTRs can help concatenate a multicast region of the network
to one that does not support native multicast.
Note there are various combinations of connectivity that can be
accomplished with the deployment of RTRs and ELPs:
* Providing multicast forwarding between IPv4-only-unicast regions
and IPv4-multicast regions.
* Providing multicast forwarding between IPv6-only-unicast regions
and IPv6-multicast regions.
* Providing multicast forwarding between IPv4-only-unicast regions
and IPv6-multicast regions.
* Providing multicast forwarding between IPv6-only-unicast regions
and IPv4-multicast regions.
* Providing multicast forwarding between IPv4-multicast regions and
IPv6-multicast regions.
An ITR or PITR can do a (S-EID,G) lookup into the mapping database.
What can be returned is a typical locator-set that could be made up
of the various RLOC addresses:
Multicast EID key: (S-EID, G)
Locator-set: ETR-A: priority 1, weight 25
ETR-B: priority 1, weight 25
g1: priority 1, weight 25
g2: priority 1, weight 25
Figure 3: An entry for host 'S-EID' sending to application group 'G'
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The locator-set above can be used as a replication list. That is
some RLOCs listed can be unicast RLOCs and some can be delivery group
RLOCs. A unicast RLOC in this case is used to encapsulate a
multicast packet originated by a multicast source EID into a unicast
packet for unicast delivery on the underlying network. ETR-A could
be an IPv4 unicast RLOC address and ETR-B could be a IPv6 unicast
RLOC address.
A delivery group address is used when a multicast packet originated
by a multicast source EID is encapsulated in a multicast packet for
multicast delivery on the underlying network. Group address 'g1'
could be an IPv4 delivery group RLOC and group address 'g2' could be
an IPv6 delivery group RLOC.
Flexibility for these various types of connectivity combinations can
be achieved and provided by the mapping database system. And the RTR
placement allows the connectivity to occur where the differences in
network functionality is located.
Extending this concept by allowing ELPs in locator-sets, one could
have this locator-set registered in the mapping database for (S-EID,
G). For example:
Multicast EID key: (S-EID, G)
Locator-set: (x, y, ETR-A): priority 1, weight 50
(a, g, b, ETR-B): priority 1, weight 50
Figure 4: Using ELPs for multicast flows
In the above situation, an ITR would encapsulate a multicast packet
originated by a multicast source EID to the RTR with unicast RLOC
'x'. Then RTR 'x' would decapsulate and unicast encapsulate to RTR
'y' ('x' or 'y' could be either IPv4 or IPv6 unicast RLOCs), which
would decapsulate and unicast encapsulate to the final RLOC 'ETR-A'.
The ETR 'ETR-A' would decapsulate and deliver the multicast packet
natively to all the receivers joined to application group 'G' inside
the LISP site.
Let's look at the ITR using the ELP (a, g, b, ETR-B). Here the
encapsulation path would be the ITR unicast encapsulates to unicast
RLOC 'a'. RTR 'a' multicast encapsulates to delivery group 'g'. The
packet gets to all ETRs that have joined delivery group 'g' so they
can deliver the multicast packet to joined receivers of application
group 'G' in their sites. RTR 'b' is also joined to delivery group
'g'. Since it is in the ELP, it will be the only RTR that unicast
encapsulates the multicast packet to ETR 'ETR-B'. Lastly, 'ETR-B'
decapsulates and delivers the multicast packet to joined receivers to
application group 'G' in its LISP site.
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As one can see there are all sorts of opportunities to provide
multicast connectivity across a network with non-congruent support
for multicast and different address-families. One can also see how
using the mapping database can allow flexible forms of delivery
policy, rerouting, and congestion control management in multicast
environments.
11. Security Considerations
When an RTR receives a LISP encapsulated packet, it can look at the
outer source address to verify that RLOC is the one listed as the
previous hop in the ELP list. If the outer source RLOC address
appears before the RLOC which matches the outer destination RLOC
address, the decapsulating RTR (or ETR if last hop), MUST choose to
drop the packet as it indicates there is a loop.
12. IANA Considerations
This document does not make any request to IANA.
13. References
13.1. 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>.
[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>.
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[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>.
[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>.
13.2. Informative References
[I-D.ermagan-lisp-nat-traversal]
Saucez, D., Iannone, L., Ermagan, V., Farinacci, D.,
Lewis, D., Maino, F., Portoles-Comeras, M., Skriver, J.,
White, C., and A. L. Brescó, "NAT traversal for LISP",
Work in Progress, Internet-Draft, draft-ermagan-lisp-nat-
traversal-20, 12 March 2025,
<https://datatracker.ietf.org/doc/html/draft-ermagan-lisp-
nat-traversal-20>.
[I-D.filyurin-lisp-elp-probing]
Filyurin, Y., Raszuk, R., Boyes, T., and D. Farinacci,
"LISP Explicit Locator Path (ELP) Probing", Work in
Progress, Internet-Draft, draft-filyurin-lisp-elp-probing-
01, 14 May 2018, <https://datatracker.ietf.org/doc/html/
draft-filyurin-lisp-elp-probing-01>.
Appendix A. Acknowledgments
The authors would like to thank the following people for their ideas
and comments. They are Albert Cabellos, Khalid Raza, and Vina
Ermagan, Gregg Schudel, Yan Filyurin, Robert Raszuk, and Truman
Boyes.
Appendix B. Document Change Log
B.1. Changes to draft-ietf-lisp-te-21
* Posted May 2025.
* Padma as Editor. Fixed IDnits findings and addressed AD comments
B.2. Changes to draft-ietf-lisp-te-20
* Posted November 2024.
* Fix IDnits findings.
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B.3. Changes to draft-ietf-lisp-te-19
* Posted June 2024.
* When describing S-bit processing change "must not" to "MUST NOT".
* Change other occurences of "must" to "MUST".
B.4. Changes to draft-ietf-lisp-te-18
* Posted June 2024.
* Add Padma clarification that an ELP should not be used if an S=1
entry is determined unreachable.
B.5. Changes to draft-ietf-lisp-te-17
* Posted June 2024.
* Made changes to reflect Padma's comments.
B.6. Changes to draft-ietf-lisp-te-16
* Posted May 2024.
* Made some document clarifications based on Luigi's comments.
B.7. Changes to draft-ietf-lisp-te-15
* Posted April 2024.
* Made changes to reflect comments from Luigi as we ready document
for standards track.
B.8. Changes to draft-ietf-lisp-te-14
* Posted February 2024.
* Update references and document timer.
B.9. Changes to draft-ietf-lisp-te-13
* Posted August 2023.
* Update references (to proposed standard documents) and document
timer.
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B.10. Changes to draft-ietf-lisp-te-12
* Posted March 2023.
* Update references (to propsed standard documents) and document
timer.
B.11. Changes to draft-ietf-lisp-te-11
* Posted September 2022.
* Update document timer and references.
B.12. Changes to draft-ietf-lisp-te-10
* Posted March 2022.
* Update document timer and references.
B.13. Changes to draft-ietf-lisp-te-09
* Posted September 2021.
* Update document timer and references.
B.14. Changes to draft-ietf-lisp-te-08
* Posted March 2021.
* Update document timer and references.
B.15. Changes to draft-ietf-lisp-te-07
* Posted October 2020.
* Update document timer and references.
B.16. Changes to draft-ietf-lisp-te-06
* Posted April 2020.
* Update document timer and references.
B.17. Changes to draft-ietf-lisp-te-05
* Posted October 2019.
* Update document timer and references.
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B.18. Changes to draft-ietf-lisp-te-04
* Posted April 2019.
* Update document timer and references.
B.19. Changes to draft-ietf-lisp-te-03
* Posted October 2018.
* Update document timer and references.
B.20. Changes to draft-ietf-lisp-te-02
* Posted April 2018.
* Update document timer and references.
B.21. Changes to draft-ietf-lisp-te-01
* Posted October 2017.
* Added section on ELP-probing that tells an ITR/RTR/PITR the
feasibility and reachability of an Explicit Locator Path.
B.22. Changes to draft-ietf-lisp-te-00
* Posted April 2017.
* Changed draft-farinacci-lisp-te-12 to working group document.
B.23. Changes to draft-farinacci-lisp-te-02 through -12
* Many postings from January 2013 through February 2017.
* Update references and document timer.
B.24. Changes to draft-farinacci-lisp-te-01.txt
* Posted July 2012.
* Add the Lookup bit to allow an ELP to be a list of encapsulation
and/or mapping database lookup addresses.
* Indicate that ELPs can be used for service chaining.
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* Add text to indicate that Map-Notify messages can be sent to new
RTRs in a ELP so their map-caches can be pre-populated to avoid
mapping database lookup packet loss.
* Fixes to editorial comments from Gregg.
B.25. Changes to draft-farinacci-lisp-te-00.txt
* Initial draft posted March 2012.
Authors' Addresses
Dino Farinacci
lispers.net
San Jose, California
United States of America
Email: farinacci@gmail.com
Michael Kowal
cisco Systems
111 Wood Avenue South
ISELIN, NJ
United States of America
Email: mikowal@cisco.com
Parantap Lahiri
Ebay
United States of America
Email: parantap.lahiri@gmail.com
Padma Pillay-Esnault (editor)
Independent
San Jose, California
United States of America
Email: padma.ietf@gmail.com
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