LISP Multicast Overlay Group to Underlay RLOC Mappings
draft-vdas-lisp-group-mapping-00
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft whose latest revision state is "Active".
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|---|---|---|---|
| Authors | Vengada Prasad Govindan , Dino Farinacci , Aswin Kuppusami , Stig Venaas | ||
| Last updated | 2023-04-24 | ||
| RFC stream | (None) | ||
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| Consensus boilerplate | Unknown | ||
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draft-vdas-lisp-group-mapping-00
Network Working Group V. Govindan, Ed.
Internet-Draft Cisco
Intended status: Experimental D. Farinacci
Expires: 26 October 2023 lispers.net
A. Kuppusami
S. Venaas
Cisco
24 April 2023
LISP Multicast Overlay Group to Underlay RLOC Mappings
draft-vdas-lisp-group-mapping-00
Abstract
This draft augments LISP [RFC9300] multicast functionality described
in [RFC6831] and [RFC8378] to support the mapping of overlay group
addresses to underlay RLOC addresses. This draft defines a many-to-
1, 1-to-many, and many-to-many relationship between multicast EIDs
and the Replication List Entries (RLEs) RLOC records they map to.
The mechanisms in this draft allow a multicast LISP overlay to run
over a mixed underlay of unicast and/or multicast packet forwarding
functionality.
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 26 October 2023.
Copyright Notice
Copyright (c) 2023 IETF Trust and the persons identified as the
document authors. All rights reserved.
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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. Requirements Language . . . . . . . . . . . . . . . . . . . . 2
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Definition of Terms . . . . . . . . . . . . . . . . . . . . . 3
4. Source Site Procedures . . . . . . . . . . . . . . . . . . . 4
5. Hashed Based Underlay Group Selection . . . . . . . . . . . . 4
6. Mapping System Lookup Based Underlay Group Selection . . . . 5
7. Receiver Site Procedures . . . . . . . . . . . . . . . . . . 6
8. Interworking with non-Overlay Receivers . . . . . . . . . . . 7
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
10. Security Considerations . . . . . . . . . . . . . . . . . . . 7
11. Normative References . . . . . . . . . . . . . . . . . . . . 7
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 8
Appendix B. Document Change Log . . . . . . . . . . . . . . . . 8
B.1. Changes to draft-vda-lisp-group-mapping-00 . . . . . . . 8
B.2. Changes to draft-vda-lisp-underlay-multicast-trees-00 . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
2. Introduction
When a multicast capable underlay connects multiple LISP sites, we
can take advantage of the multicast capabilities and perform
replication more efficiently than using head-end replication. This
draft addresses the problem of selecting the underlay multicast
group(s) to transport a given overlay multicast flow. There are 4
different scenarios possible:
1. A 1:1 mapping of a overlay multicast flow, either a (Source,
Group) or (*, Group) to an underlay group.
2. A many:1 mapping where many overlay multicast flows share the
same underlay group.
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3. A 1:many mapping where a single overlay group is transported over
different underlay groups. Note in this case, the "many" means
mapping one EID to multiple RLOCs in a RLE-set where the set can
be a mix of underlay groups and underlay unicast addresses. It
is really important that this algorithm compute unicast RLOCs as
well as multicast RLOCs.
4. Given the "many" mapping case relationship above, a 4th
relationship of m:n many-to-many mappings exist and will be
supported.
There are two methods being proposed to derive an underlay group from
an overlay group:
* Computation based underlay group assignment using a hash function.
Here all ETRs will use the same multicast underlay group, when
they are all on the same native multicast forwarding underlay.
The ETRs hash the bits of the group address G for an (S-EID, G)
flow. The low-order 24-bits of the hash is used to produce an
IPv4 underlay group address. The low-order 120-bits of the hash
is used to produce an IPv6 underlay group address.
* Lookup based group assignment where a mapping system lookup is
used to coordinate the assignment of the underlay group among
ETRs.
The scope of this draft covers underlays based on IPv4 and IPv6 only.
It does not cover other transport mechanisms like BIER, multicast
MPLS, or layer-2 underlays.
3. Definition of Terms
Note all terminology used in this document is based on the formal
definitions from [RFC6831] and [RFC8378]. The definitions below
extend these formal definitions to address the introduction of group
overlay to group/unicast underlay mappings.
(S-EID,G): refers to multicast state in multicast source and
receiver sites where S-EID is the IP address of the multicast
source host (its EID). An S-EID can appear in an IGMPv3 report,
an MSDP SA message or a PIM Join/Prune message that travels inside
of a site. The notation (S-EID,G-EID) is also used to signify
that this is an overlay source and overlay group entry.
(S-RLOC G): refers to multicast state in the underlay core where
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S-RLOC is a source address of the ITR that is performing
encapsulation. The notation (S-RLOC,G-RLOC) is also used to
denote G-RLOC as the underlay group address. The (S-RLOC,G-RLOC)
is mapped from the (S-EID,G-EID) entry by doing a mapping database
lookup for (S-EID,G-EID).
(S-RLOC,U-RLOC): refers to multicast state in the underlay core
where S-RLOC is a source address of the ITR that is performing
encapsulation. In this case, the underlay RLOC is a unicast
address and denoted as U-RLOC. A U-RLOC is used for encapsulation
when it is determined that the ETR has no multicast connectivity
and cannot be reached via a G-RLOC. So the ITR encapsulates to
the unicast address U-RLOC of the ETR.
RLE: is an Replication List Entry encoding used for replicating
multicast packets which are encapsulated. The list can be made up
of multiple G-RLOCs and U-RLOCs. The RLE appears in control
messages in a single RLOC-record.
Multicast Mapping: an entry in the mapping system that maps a
multicast (S-EID,G-EID) or (*,G-EID) entry to an RLOC-set. An
example would be EID: (S-EID,G-EID) -> RLE-set: [G-RLOCa, G-RLOCb,
U-RLOCc U-RLOCd] where the S-EID is the source of a multicast
packet sending to a G-EID destination. The RLOC-record is an RLE
entry made up of 4 replications, the first to G-RLOCa, the second
to G-RLOCb, the third to U-RLOCc, and finally to U-RLOCd. It is
at the discretion of the encapsulator (an ITR or RTR) what source
RLOC address is used as the source address in the outer header.
4. Source Site Procedures
The Source Site Procedures from [RFC8378] are followed for overlay
nodes and [RFC6831] for non-overlay nodes. There are no
modifications to these procedures other than the source multicast
site -ITR should be capable of replicating to multiple G-RLOC and
U-RLOC addresses from its map-cache.
5. Hashed Based Underlay Group Selection
When an ETR receives an IGMP/MLD report it needs to decide which
G-RLOC to underlay join. A hash-based algorithm can be used so all
ETRs that process the report can join the same G-RLOC. Therefore
when an (S-EID,G-EID) is reported, the hash will be over the pair of
32-bits for IPv4 IGMP reports and over the pair of 128-bits for IPv6
MLD reports. When (*,G-EID) is being reported, the hash is over just
G-EID. The hash function used will be sha256 [RFC6234].
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The hashed based approach creates perfect replication since it
results in a 1-to-1 mapping, but at the expense of more underlay
state.
6. Mapping System Lookup Based Underlay Group Selection
There will be scenarios where native multicast underlay provider will
want to control what group addresses are used in the network.
Therefore, a hashed based algorithm may be at conflict. In this case
G-RLOCs need to be registered to the mapping system which are part of
the provider supported group address block.
The proposed procedure is for the provider to register the G-RLOC as
an RLOC record for a distinguished-name EID encoded from procedures
in [I-D.ietf-lisp-name-encoding]. The EID will be registered in a
well defined and configured instance-id with name "group-<group-
address>".
For example, say there exists a G-EID of 224.1.1.1 and a provider
G-RLOC of 225.1.1.1. When a receiver joins G-EID 224.1.1.1, the
receiving ETR lookups up EID "group-224.1.1.1" which returns an
G-RLOC of 225.1.1.1. The ETR uses 225.1.1.1 as the G-RLOC to
register the (S-EID,G-EID) to the mapping system.
Using this method, the provider can create 1-to-many, many-to-1, and
many-to-many relationships between G-EID and G-RLOC. The provider
could also have EID "group-224.1.1.1" map to a (S-RLOC,G-RLOC) so an
SSM based distribution tree can be joined in the underlay, by either
PIM or IGMP/MLD. This example illustrates how to do a many-to-1
mapping by having multiple distinguish-name entries (encoded with
different G-EID addresses) map to a single G-RLOC.
In a many-to-many scenario, the ETR could be configured with a G-EID
set of prefixes so a power-of-2 range of G-EIDs would be looked up
that returns a single G-RLOC. For example, say there exists
224.1.0.0/16 and 224.2.0.0/16 G-EID prefix ranges and G-RLOCs
225.1.1.1 and 225.2.2.2. The provider allows only 2 underlay groups
to be used but the overlay has large ranges of G-EIDs. So the
provider registers to the mapping system "group-224.1.0.0-16" with
G-RLOC 225.1.1.1 and "group-224.2.0.0-16" with G-RLOC 225.2.2.2.
When an ETR receives an IGMP report for 224.1.1.1, it registers G-EID
224.1.1.1 with G-RLOC 225.1.1.1. It can even scale better, by
registering G-EID 224.1.0.0/16 with G-RLOC 225.1.1.1 so subsequent
IGMP reports in the 224.1.0.0/16 range would not need to be
registered. But this does come at expense of receiving multicast
packets for a G-EID when there are no receivers.
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When using multicast and G-EID prefixes, there is a tradeoff between
state in the underlay and using unnecessary bandwidth.
7. Receiver Site Procedures
The Receiver Site Procedures from [RFC8378] are followed. This draft
adds an additional step to the procedure on how should to select the
G-RLOC address for registration.
From the two approaches to obtain a G-RLOC address discussed in the
previous sections, the ETR can start and complete the (S-EID,G-EID)
registration process:
1. When ETR receives either an IGMP or MLD report, be it (S,G) or
(*,G), the entry is used as the multicast EID to Map-Register to
the mapping system. Just like [RFC6831] and [RFC8378] specify.
2. If the ETR is connected to a native multicast underlay, it will
register (S-EID,G-EID) or (*,G-EID) with a G-RLOC based on one of
G-RLOC selection options. All ETRs joining the same underlay
group for a given overlay group MUST use the same G-RLOC
selection option. For early versions of this design, the network
operator configures the option consistently in all ETRs. The
ITRs do not need such configuration since they use what the
mapping system returns.
3. If the ETR is configured to know there are ITRs that are not on
the same native multicast underlay, it MAY also register its
U-RLOC. The ITR will determine which RLOC to use by the testing
reachability via RLOC-probing according to [RFC9301].
4. Other ETRs registering the same (S-EID,G-EID) or (*,G-EID)
entries, will choose the same underlay group G-RLOC so when the
ITR replicates to G-RLOC, all ETRs receive the packet so they can
deliver to multicast receivers.
5. After the registration is performed by ETRs, they need to tell
the underlay to deliver multicast packets to them for G-RLOC.
They do that by either sending PIM-Join messages into the
underlay PIM domain or they send IGMP/MLD reports. This is left
to the implementation to decide.
If ETRs underlay join on more than one interface, they may receive
duplicate packets. Care must be taken to not IGMP/MLD join on
multiple interfaces or duplicates will occur. If PIM joining occurs
on different interfaces, RPF failures will occur to stop the
duplicates from being delivered to receivers but at the expense of
using unnecessary underlay bandwidth.
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Packet duplicates can also occur when ETRs register both G-RLOC and
their own U-RLOC addresses to the mapping system. ETRs cannot
deregister one or the other when they see duplicates because
different ITRs use the same mapping, so some will be on the multicast
underlay and some will not. In the case, when they are on a
multicast underlay, duplicates will occur across the RLOCs. The ETRs
must monitor this and not answer RLOC probes sent to the U-RLOC so
the ITR suppresses sending to it.
8. Interworking with non-Overlay Receivers
If there are multicast receivers that IGMP/MLD join a G-EID but are
not attached to a native multicast underlay, they cannot receive
multicast packets. They cannot receive multicast packets from
overlay attached sources because the ITR has no ETR to encapsulate
to. Hence, they are not on the overlay. However, if they are
attached to a native multicast underlay, they can receive multicast
packets.
There are numerous multicast connectivity combinations which are
documented in detail in [RFC6831]. Those procedures should be
followed to deliver multicast packets from overlay attached sources
to underlay only attached receivers. As well as non-overlay attach
sources to overlay attached receivers.
9. IANA Considerations
There are no requests for IANA.
10. Security Considerations
There are no security considerations at this time.
11. Normative References
[I-D.ietf-lisp-name-encoding]
Farinacci, D., "LISP Distinguished Name Encoding", Work in
Progress, Internet-Draft, draft-ietf-lisp-name-encoding-
01, 26 February 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-lisp-
name-encoding-01>.
[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>.
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[RFC6234] Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms
(SHA and SHA-based HMAC and HKDF)", RFC 6234,
DOI 10.17487/RFC6234, May 2011,
<https://www.rfc-editor.org/info/rfc6234>.
[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>.
[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>.
[RFC8378] Moreno, V. and D. Farinacci, "Signal-Free Locator/ID
Separation Protocol (LISP) Multicast", RFC 8378,
DOI 10.17487/RFC8378, May 2018,
<https://www.rfc-editor.org/info/rfc8378>.
[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>.
Appendix A. Acknowledgements
The authors would like to thank the LISP WG for their careful review
and commentary. A special thank you goes to Stig Venaas.
Appendix B. Document Change Log
B.1. Changes to draft-vda-lisp-group-mapping-00
* Submitted April 2023.
* Completed adding details to compliment [RFC6831] and [RFC8378].
* Changed name to draft-vdas-lisp-group-mapping-00 from draft-vda-
lisp-underlay-multicast-trees-00.
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B.2. Changes to draft-vda-lisp-underlay-multicast-trees-00
* Initial posting December 2020.
Authors' Addresses
Vengada Prasad Govindan (editor)
Cisco
Email: venggovi@cisco.com
Dino Farinacci
lispers.net
Email: farinacci@gmail.com
Aswin Kuppusami
Cisco
Email: aswkuppu@cisco.com
Stig Venaas
Cisco
Email: stig@cisco.com
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