Troubleshooting

Efficient Video Distribution Networks with.Multicast: IGMP Querier and PIM-DM
18
Show Commands
Description
show ip igmp snooping mrouter
Run from an IGMP snooping switch to show the
port that knows where the server is. This can be
run on any IGMP snooping switches. Other
switches will not show any entries.
show ip igmp membership
Run from the PIM router to see what VLANs and IP
interfaces have joined the multicast group.
show ip igmp groups
Shows the Querier status (routers only), IP
address, and vlan interface for each group.
Use Wireshark on each client to see the UDP protocol frames being received at the client once it joins a
multicast group (hint: the UDP packets destination address will be 239.0.0.x). Upon leaving the group
(using the stop button on the VLC player), you should notice the UDP protocol frames in Wireshark will
stop being received on the client/receiver port on the switch. If pressing the stop button on the VLC
player doesn’t stop the UDP packets from coming to the client (usually within 30 seconds), then
multicast is not working and the client ports are receiving video broadcasts. Recheck your settings and
also see Troubleshooting Tips below.
Visit http://www.wireshark.org/download.html to download the latest Wireshark.
Troubleshooting Tips
If you are receiving video at the clients but no ports are showing up under 0.0.1 or 0.0.2 from the show
ip igmp snooping groups command, then Multicast is not working. They are receiving video because
the traffic is still being broadcasted to all ports (this is the default behavior of the switches). Recheck
settings on all switches. Also read Testing the Multicast Setup.
If VLC on the client is stopped (you must press the stop button to leave the multicast group), but
Wireshark is showing UDP traffic from 239.0.0.x, then the video is being broadcasted to all ports and
multicast is not working. Check settings on all switches. Keep in mind that when the VLC client sends
a “leave group” message, that it takes a few seconds before the UDP frames stop. Also read Testing
the Multicast Setup.
Each time you want to leave the multicast group, be sure to do so by pressing the stop button at the
bottom of the VLC media player or by closing the window using the X button. Pressing pause within the
player will not leave the group.
If the UDP frames are not making it to the receiver port and no video is seen at the receiver, the time
to live (TTL) value may need to be increased when starting the stream from the server. To do this,
return to step 12 above and increase the TTL value. Then click Stream to continue.
Some MP4 files will only display the first video frame locally on the VLC Video server, but are still being
streamed to the clients, which can be verified by the progress bar below the display. To get around
this issue, stream WMV/WMA or other files.