Foundry Networks AR3202-CL - Manual (Page 223)

Foundry AR-Series Router User Guide
14 - 6 © 2004 Foundry Networks, Inc. June 2004
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.
Configuring Send
Router Alerts Foundry/configure/ip/igmp/interface ethernet0# [no] send-
router-alert
Configuring Require
Router Alerts Foundry/configure/ip/igmp/interface ethernet0# [no]
require-router-alert
Assigning filter list for
group filtering Foundry/configure/ip/igmp/interface ethernet0# group-filter
<filter-list-name#
Debug Command
Enable all debug levels Foundry/debug#[no] ip igmp all
Debug state related
events Foundry/debug#[no] ip igmp state
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
membership
information Foundry# show ip igmp groups {all | <interface-name#}
[detail]
Displaying IGMP
interface configuration Foundry# show ip igmp interface {all | <interface-name#}
Clear Command
Clearing IGMP group
membership
information Foundry# clear ip igmp groups [interface <name#] [group-
addr <addr#] [source-addr <source-addr# ]
T ABLE 6 IGMP C OMMANDS (C ONTINUED )