When I use the debug ip mpacket command I’m not getting any output. Any idea why?

First off it’s important to understand that multicast traffic is fast switched with the exception of interfaces using X.25 encapsulation. Since the multicast traffic is fast switched it will not be sent to the processor which in turn means the debug will not “see” the multicast packets. You need to disable fast switching for multicast traffic under the interfaces where the multicast traffic will transit. You can do this by using the “no ip mroute-cache” interface level command.

The exception to this is when the router has an IGMP join configured (ip igmp join-group) for a particular group. Multicast traffic destined for the joined group will be process switched and in turn the debug will be able to “see” these packets.

About Brian Dennis, CCIE #2210:

Brian Dennis has been in the networking industry for more than 22 years, with a focus on Cisco networking for the past 16 years. Brian achieved his first CCIE in Routing & Switching in 1996, and is currently the only ten year CCIE that holds five CCIE certifications. Prior to working with INE, Brian taught and developed CCIE preparation courses for various well known training organizations. Brian not only brings his years of teaching experience to the classroom, but also years of real world enterprise and service provider experience.

Find all posts by Brian Dennis, CCIE #2210 | Visit Website

You can leave a response, or trackback from your own site.

One Response to “No Output From the “debug ip mpacket” Command”

  1. Yasir Ashfaque says:

    Newer IOS do offer option of debug ip mpacket fastswitched, its really kewl.


Leave a Reply


CCIE Bloggers