Synopsis: Best practices for configuring Multicast PIM with Anycast RP for fast convergence with Brocade NetIron Family of routers.
IP multicast is deployed as an integral component in mission-critical networked applications throughout the world. These applications must be robust, hardened, and scalable to deliver the reliability that users demand.
Anycast Rendezvous Point (RP) is a mechanism that ISP or Enterprise backbones use to get fast convergence when a RP router fails since it provides load sharing and redundancy in Protocol Independent Multicast—Sparse Mode (PIM-SM) networks. Anycast RP allows two or more RPs to share the load for source registration and the ability to act as hot backup routers for each other. To allow receivers and sources to Rendezvous to the closest RP, the packets from a source need to get to all RPs to find joined receivers.
Prior to Anycast RP using the PIM mechanism, MSDP (Multicast Source Discovery Protocol) was deployed to provide a method receivers can use to find sources. Running MSDP adds more complexity with more protocol machinery from an operations perspective. To retain the Anycast RP benefits with less protocol machinery and eliminate the use of MSDP, PIM Anycast RP extends the Register mechanism in PIM so Anycast RP functionality has no dependency on MSDP.
The following documents are valuable resources for the designer. In addition, any Brocade release notes that have been published for NOS, FOS and the MLX NetIron should be reviewed.
2013-01-16 1.0 Initial Version
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Test Architect:Chris Yoon
When the source is activated in a PIM Anycast RP domain, the PIM First Hop router will register the source to the closet PIM RP. The PIM RP router will decapsulate the packet and create the (S,G) state. Since there are peers in the Anycast RP set, the PIM RP will re-encapsulate the packet as a PIM register packet with the local peering address as the source address of the encapsulation.
The PIM RP router uses unicast to send the PIM register packet to all Anycast RP peers. Once an Anycast RP peer receives the packet, it is de-capsulated and the (S,G) state is created. The PIM register packets ensures source state distribution to all RPs in a multicast domain.
Figure 1a. PIM Register machanism with two PIM Anycast RP
Figure 1b. PIM register mechanism with two PIM Anycast RP
Figure 2: PIM register mechanism with three PIM Anycast RPs
On CER/CES with NetIron 5.2 code running, with default MTU frame size (that is, 1548 bytes) configured, fragmentation for jumbo frame size’ PIM register packet was tested with two Anycast RPs set configured. 1548 bytes’ data multicast packet was sent by Tester, PIM register packet (that is, 1548 bytes + 28 bytes) generated by FH (First Hop) router was fragmented and forwarded to a close router in Anycast RP set. The router de-capsulated the fragmented PIM register packets, encapsulated as data multicast packet, and forward it to the shared tree. Then it re-encapsulated the packets as PIM register packet (that is, 1548 bytes +28 bytes) with its own address as source address, and then sends it to the other router in Anycast RP set.
With max frame size 9216 bytes configured, the same test was done for 9216 bytes’ data multicast packet.
Below is a PIM Anycast RP configuration with two RPs, RP1 and RP2:
Figure 3. PIM Anycast RP configuration
The best practice for configuring PIM Anycast RP is below:
If there are scalable multicast groups, you can configure separate Anycast RP sets for different multicast groups. This provides load sharing for the Anycast RP sets per multicast group. In the following configuration, RP1 & RP2 are an Anycast RP set for the multicast group 126.96.36.199/24, and RP3 & RP4 are an Anycast RP set for the multicast group 188.8.131.52/24.
Figure 4. PIM Anycast RP Set Load Sharing
PIM Anycast RP is supported in both IPv4 and IPv6. The following Brocade platforms support PIM Anycast RP:
This feature supports RFC 4610: Anycast-RP Using Protocol Independent Multicast (PIM).