Administrator Guide

Preventing a PIM Router from Processing a Join
To permit or deny PIM Join/Prune messages on an interface using an extended IP access list, use the following command.
NOTE: Dell Networking recommends not using the ip pim join-filter command on an interface between a source and the
RP router. Using this command in this scenario could cause problems with the PIM-SM source registration process resulting in
excessive trac being sent to the CPU of both the RP and PIM DR of the source.
Excessive trac is generated when the join process from the RP back to the source is blocked due to a new source group being
permitted in the join-lter. This results in the new source becoming stuck in registering on the DR and the continuous generation of
UDP-encapsulated registration messages between the DR and RP routers which are being sent to the CPU.
• Prevent the PIM SM router from creating state based on multicast source and/ or group.
ip pim join-filter
Understanding Multicast Traceroute (mtrace)
Multicast Traceroute (mtrace) is a multicast diagnostic facility used for tracing multicast paths.
Mtrace enables you to trace the path that a multicast packet takes from its source to the destination. When you initiate mtrace from a
source to a destination, an mtrace Query packet with IGMP type 0x1F is sent to the last-hop multicast router for the given destination. The
mtrace query packet is forwarded hop-by-hop untill it reaches the last-hop router.
NOTE
: If the system initiating the mtrace is the last-hop router, then the Query message will not be initiated. Instead, the router
sends the request message to it previous router.
The last-hop router converts this query packet to a request packet by adding a response data block. This response data block contains the
last-hop router’s interface address. The response data block inserted by the router also contains the following information:
• Incoming interface details
• Outgoing interface details
• Previous-hop router address
• Forwarding Code
• Query Arrival Time
• Routing Protocol details
The last-hop router calculates the path to reach the source in the reverse direction of the multicast data trac. Based on this calculation,
the last-hop router estimates the possible next-hop neighbor that is located in the direction towards the source and forwards the request
packet to that neighbor.
Each router along the multicast path lls its response block in a similar manner. When the mtrace request reaches the rst-hop router, it
sends the response (with IGMP type 0x1E) to the response destination address specied in the mtrace query.
The response may be returned before reaching the rst-hop router if a fatal error condition such as "no route" is encountered along the
path.
If a multicast router along the path does not implement the mtrace feature or if there is an outage, no response is returned.
When the initiator does not get a response for a specied time interval, the system performs a hop-by-hop expanding-length search to pin
point the location in the network where the problem has occurred.
NOTE
: You cannot congure the wait time. It is xed to 3 seconds.
652 Multicast Features