Multicast on same VLAN across Layer 3 Switches

[talan.westby]

Hi All,

I have a basic setup as follows:

Device A -------- 6500 VSS ---------- 3750 Stack --------- Device B

For some reason the two devices use Multicast to send their configuration despite being the only two in the group and needing to be on the same VLAN. The problem I am facing is I cannot get the Multicast traffic to traverse the two Layer 3 switches despite the traffic being on a single interface. Using Wireshark I have managed to ascertain that the traffic from Device A reaches Device B but the traffic from Device B only gets to the 6500 VSS Chassis. I cannot get it to go out of the interface to Device A.

I have managed to get the traffic working one way with static mappings for the Multicast group address however when I try and configure static mappings on the 6500 chassis it doesn't seem to like it. The mapping i am using is as follows:

ip igmp snooping vlan X static X.X.X.X interface X/X/X

On the 6500 it fails at the vlan part of the above command as if it is not supported. I have checked the software version we have and it is advanced Enterprise which from what I can see on the navigator it supports IGMP Snooping. Can anyone advise how to create a static mapping for a mutlicast group without the above command?

Thanks
Talan

[Kallol Bosu · Accepted solution]

Hey Talan,

Who is configured for IGMP snooping querier here, 6500 VSS? Is device A sending the IGMP report correctly? If it does and 6500 is configured as querier (so 3750 sees it's uplink as Mrouter port), ideally you do NOT need to do any static mapping for this scenario to work, right?

For any reason if multicast is not working as expected and you must need to do some static configuration, can you try creating a static MAC entry for the given multicast address on 6500 ?

example- (map all interfaces where the traffic needs to be forwarded to)

mac address-table static <MAC of multicast group IP> vlan <Vlan-ID> interface GigabitEthernet <x/y> GigabitEthernet <u/v>

If the above does not work then let me know. You can keep snooping disabled (not recommended) at worst case as a temp workaround. 

Regards,

Kallol

[talan.westby]

Hi Kallol,

Yes, you are correctly I shouldn't need any static mappings but it's the only way I have been able to get this far. The devices are a pain in the backside if i'm honest. To make this work I ended up creating a static MAC Entry before I seen your post.

To be honest Multicasting is one of my pet hates as the devices we get never seem to operate in the same way and we usually do all sorts just to make it work. We have another multicasting system here for video which was a proven nightmare to set up.

Anyway it's fixed now, thanks for the suggestion, will mark as correct as that is what I have set to resolve it.

Regards

Talan