Supported Protocols
The Cisco SD-WAN overlay multicast network supports the Protocol Independent Multicast (PIM) and Internet Group Management Protocol (IGMP) and multicast template configurations on all the platforms.
PIM
Cisco SD-WAN overlay multicast supports PIM version 2 (defined in RFC 4601 ), with some restrictions.
On the service side, the Cisco SD-WAN software supports native multicast. A Cisco vEdge router appears as a native PIM router and establishes PIM neighborship with other PIM routers at a local site. To properly extend multicast trees into the overlay network, a Cisco vEdge router may require other supporting routers in a local site. If a PIM-SM RP is required at a site, that function must be provided by a non-Cisco SD-WAN router, because the Cisco vEdge router currently has no native support for the rendervouz point functionality. Receivers residing downstream of a Cisco vEdge router can join multicast streams by exchanging IGMP membership reports directly with the device, and no other routers are required. This applies only to sites that have no requirement for supporting local sources or PIM SM rendezvouz points.
On the transport side, PIM-enabled Cisco SD-WAN routers originate multicast service routes (called multicast autodiscover routes), sending them using OMP to the Cisco vSmart Controllers. The multicast autodiscover routes indicate whether the router is a replicator and the local threshold. Each PIM router also conveys information learned from the PIM join messages sent by local-site multicast-enabled routers, including multicast group state, source information, and RPs. These routes assist Cisco IOS XE SD-WAN routers in performing optimized joins across the overlay when joining existing multicast sources.
Cisco SD-WAN routers support PIM source-specific mode (SSM), which allows a multicast source to be directly connected to the router.
PIM Scalability Information
When configuring PIM, the following scalability limits apply:
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Any single Cisco vEdge router supports a maximum of 1024 multicast state entries. Note that a (*,G) and an (S,G) for the same group count as two entries.
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The 1024 multicast state entries are shared across all configured VPNs on a single Cisco vEdge router.
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Each state entry can contain a maximum of 64 service-side entries and a maximum of 256 transport-side entries in its outgoing interface list (OIL).
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Starting from Cisco SD-WAN Release 20.7.2, in the Cisco SD-WAN overlay, you can have a maximum of 512 multicast enabled Cisco vEdge devices per VPN.
Rendezvous Points
The root of a PIM multicast shared tree resides on a router configured to be a rendezvous point (RP). Each RP acts as the RP and the root of a shared tree (or trees) for specific multicast group ranges. In the Cisco SD-WAN overlay network, RPs are non-Cisco SD-WAN routers that reside in the local-site network. The RP function is typically assigned to one or two locations in the network; it is not required at every site. Cisco vEdge routers do not currently support the RP functionality, so non-Cisco SD-WAN routers must provide this function in the applicable sites.
The Cisco SD-WAN software supports the auto-RP protocol for distributing RP-to-group mapping information to local-site PIM routers. With this information, each PIM router has the ability to forward joins to the correct RP for the group that a downstream IGMP client is attempting to join. Auto-RP updates are propagated to downstream PIM routers if such routers are present in the local site.
Replicators
For efficient use of WAN bandwidth, strategic Cisco SD-WAN routers can be deployed and configured as replicators throughout the overlay network. Replicators mitigate the requirement for a Cisco SD-WAN router with local sources or the PIM-RP to replicate a multicast stream once for each receiver. As discussed above, replicators advertise themselves, using OMP multicast-autodiscover routes, to the Cisco vSmart Controllers in the overlay network. The controllers then forward the replicator location information to the PIM-enabled Cisco IOS XE SD-WAN routers that are in the same VPN as the replicator.
A replicator Cisco SD-WAN router receives streams from multicast sources, replicates them, and forwards them to other Cisco SD-WAN routers with multicast receivers in the same VPN. The details of the replication process are discussed below, in the section Multicast Traffic Flow through the Overlay Network. A replicator is typically a Cisco IOS XE SD-WAN router located at a colo-site or another site with a higher-speed connection to the WAN transport network.
Multicast Service Routes
Cisco SD-WAN routers send multicast service routes to the Cisco vSmart Controller using OMP. From these routes, the controller processes and forwards joins for requested multicast groups towards the source address or PIM-RP as specified in the original PIM join message that resulted in a Cisco SD-WAN router advertising the OMP multicast service route. The source address can be either the IP address of an RP if the originating router is attempting to join the PIM shared tree or the IP address of the actual source of the multicast stream if the originating router is attempting to join the source tree.
IGMP
Cisco SD-WAN overlay multicast routing supports the Internet Group Management Protocol (IGMP) version 2 (defined in RFC 2236 ). Cisco vEdge devices use IGMP to process receiver membership reports for the hosts in a particular VPN and to determine, for a given group, whether multicast traffic should be forwarded and state should be maintained. vEdge routers listen for both IGMPv1 and IGMPv2 group membership reports.