LISP Working Group V. Govindan
Internet-Draft M. Hamroz
Intended status: Informational J. Gawron
Expires: 4 October 2025 Cisco
2 April 2025
LISP Multicast Deployment Experience
draft-vgovindan-lisp-multicast-deploy-01
Abstract
We present our experiences in supporting deployments of LISP
Multicast using unicast and multicast underlays. This document
details design considerations that can be useful for anyone
interested in deploying LISP multicast services over IP networks.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Scope of this document . . . . . . . . . . . . . . . . . . . 3
4. Scope not covered by this document . . . . . . . . . . . . . 3
5. Industry segments/ use-cases covered . . . . . . . . . . . . 3
6. Advantages and Cost of using "PIM-over-PIM" . . . . . . . . . 3
7. Underlay Deployment considerations . . . . . . . . . . . . . 4
7.1. Head-End Replication . . . . . . . . . . . . . . . . . . 4
7.2. Native Multicast Underlay . . . . . . . . . . . . . . . . 5
8. Layer-2 BUM overlay deployment considerations . . . . . . . . 5
8.1. RP for Layer-2 BUM Multicast Underlay . . . . . . . . . . 6
9. Layer-3 overlay Multicast deployment considerations . . . . . 6
9.1. Layer-3 Routed Any-Source Multicast (ASM) services . . . 6
9.1.1. Layer-3 overlay ASM RP placement and redundancy . . . 7
9.1.2. Optimisation for short-lived streams . . . . . . . . 7
9.2. Layer-3 Routed SSM services . . . . . . . . . . . . . . . 7
10. Mobility considerations for LISP multicast . . . . . . . . . 8
11. Enabling Multicast flows for multiple tenants and multiple site
overlays . . . . . . . . . . . . . . . . . . . . . . . . 8
11.1. Background reading . . . . . . . . . . . . . . . . . . . 8
11.2. LISP Uberlay deployment considerations . . . . . . . . . 8
12. Extranet Multicast (Route leaking) . . . . . . . . . . . . . 9
13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
14. Security Considerations . . . . . . . . . . . . . . . . . . . 9
15. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
15.1. Normative References . . . . . . . . . . . . . . . . . . 9
15.2. Informative References . . . . . . . . . . . . . . . . . 10
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 11
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
This document describes deployment experiences of inter domain
multicast routing function in a network where Locator/ID Separation
is deployed using the Locator/ID Separation Protocol (LISP)
architecture as described in [I-D.ietf-lisp-rfc6831bis]
2. Terminology
All of the terminology used in this document comes from [RFC9301]
[I-D.ietf-lisp-rfc6831bis], [I-D.ietf-lisp-vpn] and
[I-D.moreno-lisp-uberlay].
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3. Scope of this document
This document covers the following aspects:
* Deployments based on the procedures of [I-D.ietf-lisp-rfc6831bis].
* When using a multicast based underlay, LISP sites can provide
support to forward Layer-2 Broadcast, Unknown Unicast and
Multicast (BUM) packets.
* Layer3 routed multicast services (ASM, SSM and BiDir) are provided
by such LISP sites.
* Both IPv4 and IPv6 overlays are covered by this document.
Similarly, both IPv4 and IPv6 underlays are covered.
4. Scope not covered by this document
This document does not cover the following aspects:
* L3 routed Unicast forwarding or L2 forwarding between LISP sites.
* This document does not address services implemented using
underlays such as BIER.
* Procedures and considerations required for migrating non-LISP
based networks to LISP based networks.
* Extranet Multicast (Route Leaking).
* Signal Free LISP Multicast [I-D.ietf-lisp-rfc8378bis].
5. Industry segments/ use-cases covered
The deployment experiences outlined in this document capture
learnings from various industry segments listed below (not
exhaustive:)
* Educational Institutions (e.g. Universities with multiple
campuses, school districts)
* Public Utilities like Airports, Stadiums and Ports
* Hospitals and Healthcare providers
* Enterprises including Financial Institutions spread across
continents and large geographical regions
* Technology vendors and factories
* Events like Expos, Tradeshows, Sporting events
6. Advantages and Cost of using "PIM-over-PIM"
There are both advantages and costs in using a "PIM-over-PIM" design
outlined in [I-D.ietf-lisp-rfc6831bis]:
* PIM [RFC7761] is a well-understood and deployed protocol in many
types of networks (Enterprise, Global Internet etc.).
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* For the specific case of deploying PIM in the overlay in a LISP
network, merely encapsulating the PIM protocol packet into a
Unicast LISP packet and directing it towards the xTR that is
chosen as the Upstream Multicast NH worked very well.
* Usage of PIM Join Attributes for LISP is a very useful method for
the receiver ETR to signal underlay transport attributes to the
ITR [RFC8059]. The motivations for doing so are explained in the
later sections of this document.
* The PIM neighborship was not fully established as exchange of PIM
hellos were considered chatty. An alternate method of achieving
this could be to use [RFC9739]
* A simple but powerful optimization was done to use only SSM in the
underlay for supporting overlay Layer-3 multicast routing.
7. Underlay Deployment considerations
7.1. Head-End Replication
A small but significant subset of deployments have been observed
using the Head-End Replication (HER). This is primarily done for
low-volume multicast or for deployments where there are restrictions
in implementations for supporting an underlay with native multicast.
Another category of the deployments were early adopters of the
technology when the software releases were limited to unicast
underlay.
The primary characteristic of such networks is the presence of a
limited number of LISP sites in which receivers are present. Please
note that this does not necessarily mean that only a limited number
of hosts receive the multicast.
Since the ASICs that form the data plane have very efficient methods
to replicate multicast packets to local receivers, any deployment
that has a good localization of receivers to a limited number of LISP
sites can still use a unicast underlay with high efficiency.
On the positive side, there are widely deployed mechanisms for both
traffic-engineering (e.g. Load balancing) and fast convergence due to
link/ node failures in unicast that can be reused for overlay routed
multicast when using a unicast underlay.
Another very important use-case for considering a unicast underlay is
to have migration done from (say) IPv4 to IPv6.
It is also possible to perform the Head-End replication on an ITR or
PITR.
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Although not covered in this document, the design of HER allows for
the co-existence of RLOCs using both unicast and multicast underlays.
7.2. Native Multicast Underlay
Native multicast underlay presents notable advantages over Head-End
Replication, particularly in network topologies where replication
occurs at multiple nodes between the ETR and the ITR. Despite
advancements in modern ASICs designed for high-performance multicast
packet replication at the Head-End, bandwidth consumption remains a
critical factor favoring the adoption of native multicast underlay.
In native multicast mode, there is a mapping between the overlay
multicast group address and the underlay multicast group. This
mapping must be consistent across network devices within a LISP
domain to ensure uniformity. The simplest method involves a 1:1
mapping between the overlay LISP group address and the underlay
multicast group address. To maintain uniqueness in this mapping
process, implementations may incorporate additional parameters, such
as the source IP address and LISP instance ID, providing sufficient
entropy to ensure uniqueness across LISP instances.
There exists recent work like [I-D.ietf-lisp-group-mapping] that can
be leveraged here.
Using native multicast in the underlay is used by the majority of the
deployments known.
* Underlays in most deployments were homogenous e.g. IPv6 Unicast
based underlay.
* Upgrading from one underlay to another is a process that requires
a lot of planning. This is not covered in this document.
8. Layer-2 BUM overlay deployment considerations
There are three deployment options that can be considered here for
deployment:
* Ingress Replication: Each L2 BUM packet is replicated by the ITR
so each ETR receives a copy of the L2 packet encapsulated as
unicast in the underlay.
* Use ASM underlay: Since any xTR does not know the list of ITRs
that can potentially send L2 BUM packets, it subscribes to an
underlay multicast group based on the L2 LISP instance. There can
be a m:n mapping of 'm' LISP instances to 'n' Underlay Multicast
groups with m>n or m>>n. We have also seen many customers use
n=1.
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* Use BIDIR underlay: Since BIDIR is a commonly supported mode we
can simply reduce the multicast state in the underlay to O(n)
instead of O(n*no.of ITRs) by choosing BIDIR over ASM. This mode
is particularly popular when IPv6 underlay is used as the
forwarding path resources (e.g. TCAM entries) required to support
IPv6 multicast routing is double that of IPv4.
8.1. RP for Layer-2 BUM Multicast Underlay
* When using a Multicast underlay for L2 BUM, we use ASM based
underlay or a BIDIR based underlay.
* This can be achieved by having an m LISP L2 service instances are
mapped to n multicast groups where m > n or m >> n since the
number of LISP L2 instances are larger than the number of
designated multicast groups to carry BUM traffic.
* Since this is done flexibly, heavy users of BUM can be allocated
separate underlay groups for isolation.
* One of the most critical design element is the choice of the RP
Design. We have the following options:
- Configuring static RPs: Use of anycast IP addresses with static
RP is a popular choice observed in deployments.
- Electing RPs through mechanisms like PIM-BSR [RFC5059] has been
adopted by customers as well.
- Discovering RPs via the Mapping system is not covered in this
document.
9. Layer-3 overlay Multicast deployment considerations
9.1. Layer-3 Routed Any-Source Multicast (ASM) services
LISP overlays extend ASM to networks lacking native multicast support
traditionally. Native multicast in the core boosts ASM resilience
and optimizes traffic distribution.
Head-end replication requires tuning to avoid ITR overload with many
receivers or high traffic. LISP overlays enable ASM resilience by
rerouting around underlay failures dynamically.
ASM deployments scale receiver counts flexibly without requiring
underlay redesigns. Troubleshooting ASM demands monitoring both LISP
overlay and underlay states concurrently.
Pre-validating underlay multicast capabilities ensures reliable ASM
performance consistently. Using native multicast complicates failure
diagnosis despite enhancing overall resilience.
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9.1.1. Layer-3 overlay ASM RP placement and redundancy
In a Layer-3 overlay, the placement of RPs is critical for ensuring
robust multicast service delivery. Unlike traditional PIM-ASM, LISP
multicast relies on static Rendezvous Point (RP) configurations due
to the lack of support for dynamic RP discovery mechanisms like Auto-
RP or Bootstrap Router (BSR).
Discovering RPs via the mapping system is possible but not covered in
this document.
RPs can be positioned both inside and outside the LISP domain. The
typical configuration involves static RP setup and redundancy through
the Anycast RP concept, which allows multiple RPs to share the same
IP address, providing load balancing and fault tolerance. This setup
requires synchronization between RPs using the MSDP to exchange
information about active sources.
In some deployments, RP placements are a combination of RPs placed
inside together with RPs placed outside the LISP domains. This
configuration leverages advanced MSDP peering or group mesh peering
to enhance multicast service resilience and efficiency.
The RP placement significantly affects the convergence between the
shared and source trees. It is essential that all xTRs within a
given LISP instance use a consistent address scheme with identical
mapping to ensure efficient multicast routing. The RP facilitates
the initial setup of the sharedi tree, allowing sources and receivers
to establish direct multicast data flows.
9.1.2. Optimisation for short-lived streams
When working with short lived streams (e.g. PA systems for airports)
it was observed that using the shared tree was optimal. The cost of
switching to the shortest-path tree can be avoided in such scenarios.
However such choices are better done on a case-by-case basis e.g.
based on the range of group addresses.
9.2. Layer-3 Routed SSM services
SSM services over a Layer-3 LISP domain connect multicast sources and
receivers via the overlay. Receivers join source trees (S,G) by
signalling IGMPv3, which then is transported as PIM packets over the
LISP overlay. The typical SSM services would be represented by
Financial Data, IPTV and Live streaming applications.
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The traffic within a LISP domain, similar to the ASM would be subject
to encapsulation and depending on the multicast mode it would be
either head-end replication or native (overlay to underlay multicast
mapping).
The sources and receivers can be connected to the LISP site or be
located outside of the LISP domain. LISP overlay provides a
resiliency by rerouting traffic dynamically.
SSM services eliminate RPs and shared trees, simplifying tree
management. Direct (S,G) trees enhance scalability and reduce
latency for one-to-many uses.
Receivers must support IGMPv3 (or MLDv2) to specify sources, avoiding
ASM fallback. Replication strategies need tuning to balance ITR load
and underlay bandwidth.
10. Mobility considerations for LISP multicast
TBD
11. Enabling Multicast flows for multiple tenants and multiple site
overlays
11.1. Background reading
[I-D.moreno-lisp-uberlay] provides methods to operate and
interconnect multiple LISP sites using Border xTR nodes.
[I-D.ietf-lisp-vpn] describes the use of the LISP to create Virtual
Private Networks (VPNs). LISP is used to provide segmentation in
both the LISP data plane and control plane.
Using the procedures and construct of the above two references, we
have been to able to build and deploy solutions that cater to
multiple tenants connected to multiple LISP sites spread across
multiple site overlays.
11.2. LISP Uberlay deployment considerations
One of the primary deployment use cases involves delivering multicast
services across multiple site overlays or RLOC spaces
[I-D.moreno-lisp-uberlay]. There are several methods for routing
multicast packets when sources and recievers are connected to LISP
site overlays that are connected through VPNs. Two most common
methods are given below:
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* Forwarding the traffic natively, without any encapsulation, which
typically results in extending the Forwarding Context
[I-D.ietf-lisp-vpn] segmentation beyond a specific LISP site
overlay.
* Implementing an overlay across the uberlay network.
Choosing between these options has significant design implications
for both unicast and multicast flows:
In the native forwarding approach, traffic leaving a site overlay is
decapsulated at the border xTRs and placed into the appropriate VRF
corresponding to the Forwarding Context. This scenario creates
considerable overhead in deploying multicast configurations across
multiple site overlays, as each LISP Forwarding Context must be
mapped to an individual VRF in uberlay.
Implementing an overlay over the LISP uberlay network offers
advantages by extending the LISP Forwarding Context between different
LISP domains. In this case, Border xTRs in each LISP domain are
responsible for decapsulating and re-encapsulating traffic between
different site overlays. This can be achieved by using disjoint
underlay multicast groups in the different site overlays/ uberlay.
PIM can be leveraged for signaling the different underlay group
mappings for the site-overlays and uberlay. [RFC8059]
12. Extranet Multicast (Route leaking)
This feature is beyond the scope of this document.
13. IANA Considerations
This memo includes no request to IANA.
14. Security Considerations
This informational document does not introduce any new security
considerations.
15. References
15.1. Normative References
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[I-D.ietf-lisp-rfc6831bis]
Farinacci, D., Meyer, D., Zwiebel, J., Venaas, S., and V.
P. Govindan, "The Locator/ID Separation Protocol (LISP)
for Multicast Environments", Work in Progress, Internet-
Draft, draft-ietf-lisp-rfc6831bis-01, 29 January 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-lisp-
rfc6831bis-01>.
[I-D.ietf-lisp-rfc8378bis]
Moreno, V. and D. Farinacci, "Signal-Free Locator/ID
Separation Protocol (LISP) Multicast", Work in Progress,
Internet-Draft, draft-ietf-lisp-rfc8378bis-03, 25 February
2025, <https://datatracker.ietf.org/doc/html/draft-ietf-
lisp-rfc8378bis-03>.
[RFC5059] Bhaskar, N., Gall, A., Lingard, J., and S. Venaas,
"Bootstrap Router (BSR) Mechanism for Protocol Independent
Multicast (PIM)", RFC 5059, DOI 10.17487/RFC5059, January
2008, <https://www.rfc-editor.org/info/rfc5059>.
[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>.
[RFC8059] Arango, J., Venaas, S., Kouvelas, I., and D. Farinacci,
"PIM Join Attributes for Locator/ID Separation Protocol
(LISP) Environments", RFC 8059, DOI 10.17487/RFC8059,
January 2017, <https://www.rfc-editor.org/info/rfc8059>.
[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>.
15.2. Informative References
[I-D.ietf-lisp-group-mapping]
Govindan, V. P., Farinacci, D., Kuppusami, A., and S.
Venaas, "LISP Multicast Overlay Group to Underlay RLOC
Mappings", Work in Progress, Internet-Draft, draft-ietf-
lisp-group-mapping-01, 11 November 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-lisp-
group-mapping-01>.
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[I-D.ietf-lisp-vpn]
Moreno, V. and D. Farinacci, "LISP Virtual Private
Networks (VPNs)", Work in Progress, Internet-Draft, draft-
ietf-lisp-vpn-12, 19 September 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-lisp-
vpn-12>.
[I-D.moreno-lisp-uberlay]
Moreno, V., Farinacci, D., Rodriguez-Natal, A., Portoles-
Comeras, M., Maino, F., and S. Hooda, "Uberlay
Interconnection of Multiple LISP overlays", Work in
Progress, Internet-Draft, draft-moreno-lisp-uberlay-06, 28
September 2022, <https://datatracker.ietf.org/doc/html/
draft-moreno-lisp-uberlay-06>.
[RFC9739] Bidgoli, H., Ed., Venaas, S., Mishra, M., Zhang, Z., and
M. McBride, "Protocol Independent Multicast Light (PIM
Light)", RFC 9739, DOI 10.17487/RFC9739, March 2025,
<https://www.rfc-editor.org/info/rfc9739>.
Acknowledgements
A very special and sincere thanks to Dino Farinacci for his extensive
and insightful comments for improving the content and the readability
of this document.
The authors would like to acknowledge Stig Venaas for his review.
Many individuals also contributed to the discussions for the material
of this draft including Arunkumar Nandakumar, Aswin Kuppusami,
Rajavel Ganesamoorthy, Sankar S and Sundara Moorthy. All
contributions are gratefully acknowledged.
Contributors
TBD
Authors' Addresses
Vengada Prasad Govindan
Cisco
Email: venggovi@cisco.com
Marcin Hamroz
Cisco
Email: mhamroz@cisco.com
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Jaroslaw Gawron
Cisco
Email: jagawron@cisco.com
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