Checking the Groups for Which a PIM-SM Router Maintains Join State

Problem

PIM-SM is enabled on all routers, and each router has discovered an RP. You want to check that the router has joined the desired multicast groups.

Solution

Look at the Join messages to see the groups for which the PIM router maintains join state:

	aviva@RouterA> show pim join
	Instance: PIM.master Family: INET
	Group: 224.0.1.39
	 Source: *
	 RP: 192.168.13.1
	 Flags: sparse,rptree,wildcard
	 Upstream interface: local
	Group: 224.0.1.40
	 Source: *
	 RP: 192.168.13.1
	 Flags: sparse,rptree,wildcard
	 Upstream interface: local
	Group: 224.1.1.1
	 Source: *
	 RP: 192.168.13.1
	 Flags: sparse,rptree,wildcard
	 Upstream interface: local
	Group: 224.1.1.1
	 Source: 10.0.15.1
	 Flags: sparse
	 Upstream interface: fe-0/0/1.0
	Group: 224.2.127.254
	 Source: *
	 RP: 192.168.13.1
	 Flags: sparse,rptree,wildcard
	 Upstream interface: local
	Group: 230.0.1.1
	 Source: *
	 RP: 192.168.13.1
	 Flags: sparse,rptree,wildcard
	 Upstream interface: local
	Instance: PIM.master Family: INET6

The extensive version of this command gives the details for each multicast group:

	aviva@RouterA> show pim join extensive 224.1.1.1
	Instance: PIM.master Family: INET
	Group: 224.1.1.1
	 Source: *
	 RP: 192.168.13.1
	 Flags: sparse,rptree,wildcard
	 Upstream interface: local
	 Upstream neighbor: Local
	 Upstream State: Local RP
	 Downstream Neighbors:
	 Interface: se-0/0/3.0
	 10.0.16.2 State: Join Flags: SRW Timeout: 165
	Group: 224.1.1.1
	 Source: 10.0.15.1

	 Flags: sparse
	 Upstream interface: fe-0/0/1.0
	 Upstream neighbor: 10.0.15.1
	 Upstream State: Local Source, Local RP
	 Keepalive timeout: 116
	 Downstream Neighbors:
	 Interface: se-0/0/3.0
	 10.0.16.2 State: 
Join Flags: S Timeout: 165

Discussion

When a host connected to a PIM router informs the router that it wants to receive traffic from a multicast group, the PIM router sends (S,G) Join messages out its RPF interfaces to inform the next upstream router that it wants to receive packets for that group. Each upstream router repeats this process until this branch of the multicast tree reaches the router directly connected to the multicast source or reaches a router that already has multicast forwarding state for the (S,G) pair.

The show pim join command lists all groups the router has sent Join messages to and has successfully joined. The output in this recipe indicates that RouterA has joined six multicast groups. For each group, you see the multicast source of the group. This is either the IP address of a source router or an asterisk (*)if the Join message is directed toward any source. The RP line shows the address of the rendezvous point for the group, and Upstream interface is the routers interface toward the groups source.

The extensive version of the command shows the upstream state, which is information about the upstream router, and downstream interfaces toward the multicast receiver.

The output of the show pim join extensive command for group 224.1.1.1 agrees with the route information displayed with the show multicast route extensive command (explained in Recipe 16.9):

	aviva@RouterA> show multicast route extensive
	Address family INET
	Group: 224.1.1.1
	 Source: 10.0.15.1/32
	 Upstream interface: fe-0/0/1.0
	 Downstream interface list:
	 se-0/0/3.0
	 Session description: ST Multicast Groups
	 Statistics: 0 kBps, 0 pps, 5 packets
	 Next-hop ID: 359
	 Upstream protocol: PIM
	 Route state: Active
	 Forwarding state: Forwarding
	 Cache lifetime/timeout: 356 seconds
	 Wrong incoming interface notifications: 0

The information these two commands displays is subtly different. The show multicast route command describes forwarding plane information, while the show pim join command covers the control plane. The information in the two commands should agree, but each command shows some information that the other does not.

See Also

Recipe 16.9


Router Configuration and File Management

Basic Router Security and Access Control

IPSec

SNMP

Logging

NTP

Router Interfaces

IP Routing

Routing Policy and Firewall Filters

RIP

IS-IS

OSPF

BGP

MPLS

VPNs

IP Multicast



JUNOS Cookbook
Junos Cookbook (Cookbooks (OReilly))
ISBN: 0596100140
EAN: 2147483647
Year: 2007
Pages: 290
Authors: Aviva Garrett

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