PIM

Terminology

• PIM Designated Router (DR): The DR is the router that will forward the PIM join message from the receiver to the RP (rendezvous point). Since the DR is used to forward PIM join messages to the RP, it doesn’t do much good for multicast dense mode where we don’t have an RP. The only exception is when you use IGMPv1…in that case, the PIM DR will work as the IGMP query router because IGMPv1 doesn’t have a query router election

• PIM Forwarder: the router that will forward multicast in a segment with multiple PIM neighbors

PIM Mode

PIM-SM (Sparse Mode)

• uses RP (Rendervous Point) as a central point where routers can register multicast sources on directly connected subnet

Auto RP

• define multiple candidate RPs, so that if an RP fails, other candidate RP can assume the responsibility of the RP

• A candidate RP sends RP announcement messages to the RP announce group (224.0.1.39) to announce the router as a candidate for RP for a specific multicast group

• A mapping agent joins the RP announce group (224.0.1.39) to receive RP candidate announcements, saves and selects the highest IP address as the RP for the group

• The mapping agent then multicast its group-to-RP mapping to the RP discovery group (224.0.1.40), which Cisco routers automatically join to learn about RP for each group

Configuration

# Manually Configure RP
Nexus(config)# feature pim
Nexus(config)# interface ethernet 1/1-2
Nexus(config-if-range)# ip pim sparse-mode
Nexus(config)# ip pim rp-address 10.10.10.10 group-list 224.0.0.0/9

# Auto RP
Nexus-RP(config)# ip pim auto-rp rp-candidate ethernet 2/1 group-list 239.0.0.0/24
Nexus-RP(config)# ip pim auto-rp mapping agent ethernet 2/1

Verification

• show ip pim interface brief

• show ip pim neighbor

• show ip pim rp

• show ip pim group-range

• show ip mroute 239.1.1.1

PIM-DM (Dense Mode)

• builds SPF tree by flooding multicast traffic to all branches, then prunes back where no receivers are present

• Not supported on NX-OS

BIDIR-PIM (Bidirectional PIM)

• used for many to many multicast applications. Allows traffic to flow both up and down the shared tree from RP.

• Used with VXLAN

PIM-SSM (Source Specific Multicast)

• Uses only source-based trees. Requires receivers to signal source that it's interested in using IGMPv3

MSDP (Multicast Source Discovery Protocol)

• Announces multicast sources between RPs in different domains