Foundry Networks AR1208, AR3202-CL, AR3201-CL, AR1204, AR1216 Traceroute Facility for IP Multicast

Foundry AR-Series Router User Guide

TABLE 6 IGMP COMMANDS (CONTINUED)

Configuring Send	Foundry/configure/ip/igmp/interface ethernet0# [no] send-
Router Alerts	router-alert
Configuring Require	Foundry/configure/ip/igmp/interface ethernet0# [no]
Router Alerts	require-router-alert
Assigning filter list for	Foundry/configure/ip/igmp/interface ethernet0# group-filter
group filtering	<filter-list-name#
Debug Command
Enable all debug levels	Foundry/debug#[no]	ip igmp all
Debug state related	Foundry/debug#[no]	ip igmp state
events
Debug normal events	Foundry/debug#[no]	ip igmp normal
Debug query packets	Foundry/debug#[no]	ip igmp	packet query	[inbound
	outbound]
Debug report packets	Foundry/debug#[no]	ip igmp	packet report	[inbound
	outbound]
Debug leave packets	Foundry/debug#[no]	ip igmp	packet leave	[inbound
	outbound]
Show Commands
Displaying IGMP group	Foundry# show ip igmp groups {all <interface-name#}
membership	[detail]
information
Displaying IGMP	Foundry# show ip igmp interface {all <interface-name#}
interface configuration
Clear Command
Clearing IGMP group	Foundry# clear ip igmp groups [interface <name#] [group-
membership	addr <addr#] [source-addr <source-addr# ]
information

Traceroute Facility for IP Multicast

With multicast distribution trees, tracing from a source to a multicast destination is difficult, since the branch of the multicast tree on which the destination lies is unknown. The technique used by the traceroute tool to trace unicast network paths will not work for IP multicast because traceroute (ICMP) responses are specifically forbidden for multicast traffic. Thus, you have to flood the whole tree to find the path from one source to one destination. However, walking up the tree from destination to source is easy, as most existing multicast routing protocols know the previous hop for each source. Tracing from destination to source involves only routers on the direct path.

To request a traceroute (which does not have to be the source or the destination), send a traceroute query packet to the last-hop multicast router for the given destination. The last-hop router turns the query into a request packet by adding a response data block containing its interface addresses and packet statistics, and then forwards the request packet using unicast to the router that it believes is the proper previous hop for the given source and group. Each hop adds its response data to the end of the request packet, then unicast forwards it to the previous hop. The first hop router (the router that believes that packets from the source originate on one of its directly connected networks) changes the packet type to indicate a response packet and sends the completed response to the response destination address. The response may be returned before reaching the first hop router if a fatal error condition such as “no route” is encountered along the path.

14 - 6 © 2004 Foundry Networks, Inc. June 2004