Multicast routing on C2960XR

[triton.milossedlacek]

Dear All,

We are testing the WS-C2960XR-24TS-I for use in video applications dealing with IP multicasts. I want to ask if these switches (or routers) are suitable for routing of multicasts. We did notice that if we route multicasts between VLANs (inter-VLAN routing) then the CPU load gets significanlty higher (up to 100%).

Is what we experience the normal behavior and the switch does not suit the multicast routing applications? 

[triton.milossedlacek]

Yes, we re-enabled them back then. So now it works with the same configuration and same load as before. It seems we really got rid of some jammed process.

[Mark Malone]

That's interesting hopefully it stays like that :)

thanks for letting us know the fix in the end

[Jon Marshall]

The IP Input process is used when packets are sent to the main CPU to be processed switched ie. not hardware switched.

I haven't used those switches so it may be you are simply pushing too much traffic but there are also many reasons why multicast traffic may be processed switch so it's difficult to say what the reason is at the moment.

You may want to have a read of this link which covers a lot of the causes of multicast packets being processed switched -

https://supportforums.cisco.com/blog/153786

a particularly common cause is the TTL setting in the multicast packets being wrong.

Jon

[triton.milossedlacek]

Hello Guys, thank you for our time.

I'll collect all the info Mark is proposing.

I also find the article Jon is sharing with me extremely interesting. Note we have this configured in our switch

interface Vlan101
ip address 10.100.29.253 255.255.255.252
ip pim sparse-dense-mode
ip igmp join-group 239.255.1.10
ip igmp join-group 239.255.1.9
ip igmp join-group 239.255.1.8
ip igmp join-group 239.255.1.7
ip igmp join-group 239.255.1.6
ip igmp join-group 239.255.1.5
ip igmp join-group 239.255.1.4
ip igmp join-group 239.255.1.3
ip igmp join-group 239.255.1.2
ip igmp join-group 239.255.1.1
ip igmp join-group 239.0.0.2
ip igmp version 3
shutdown

According the blog these multicasts are always send to the CPU. That could be explanation. But, the VLAN for which it is configured is administratively shutdown. Would such multicast be sent to CPU anyway? ... anyway I'll unconfigure these lines as my first try.