SG300-28P Multicast (IGMP) and IGMP routing..

[jsterck]

A brief background on the setup:

I recently switched out my switch.  It was a Cisco 3750 10/100 switch and I wanted to upgrade to Gig.  The cost of a Gig+POE 3750 is too much to bite so I opted for the SG300.  My router is a Cisco 891.  Here is the setup:

Cisco 891:

two SVI's: vlan1 and vlan 100

Vlan1 = 10.0.1.1/24

Vlan100 = 10.0.100.2/24

Connected to SG300 via Fa0

DHCP Server for vlan1+vlan100

Cisco SG300-28P:

two SVI's: vlan 1 and vlan 100

vlan 1 = 10.0.1.21/24

vlan 100 = 10.0.100.1/24

Connected to 891 on via Gi18

The connection between 891 and SG300 = trunk, vlan1-u, vlan100-t

The problem:

With the 891+3750, I was able to add "ip pim sparse-dense-mode" on all the SVI's and hosts could join any multicast group, irregardless of which vlan the host was a member of.

Now I've changed switches, and I dont get the same love.  I have the PIM statement on both SVI's on the 891, but Im unsure of what I need to configure on the SG300.  I have enabled "Bridge multicast filtering" + "IGMP snooping".  What can I do to get similar functionality using the SG300 + 891?  I assume this is my lack of understanding IGMP in general, but was able to get away with it using the PIM statements on the 891+3750 stack.

Jeff

[Tom Watts]

Hi Jeff, you need to enable the IGMP status per SVI.

Multicast-> IGMP snooping

Choose the vlan then make sure IGMP snooping is enabled. You can also enable the querier status. You can have only 1 querier per SVI, any additional querier will become standby.

IGMP should dynamically take care of the rest for finding the mrouter port and also build the mac/ip groups when it is listening. If you still have some problems, you may have to filter unregistered multicast. It can make the known groups bounce.

[jsterck]

Thanks for the very prompt response Tom.  I am curious as to what you mean about filtering unregistered multicast.  I think this may be part of the problem Im seeing.  It seems like when im doing "sh ip igmp members" it seems like instead of showing multipe members, it shows one member, but the member will change (like its stomping on the previous member). 

If I look at the switch for Unrigestered multicast, I see the options being filtering by port.  How would I deduce what port I need to filter on?

Jeff

[Tom Watts]

You should be able to filter unregisted multicast on every port.

To be able to pass multicast over subnets two things must be certain, the node/device is able to send and receive multicast packets but also register the multicast address being listened to by the node so the local and remote routers can route the multicast packets.

When the switch learns a multicast address through IGMP snooping, this is a registered multicast. The switch will only forward multicast to ports that are registered to the multicast group. Where unregistered multicast comes in, is the multicast that is not statically defined or learned through IGMP which in turn will be forwarded to all ports of the vlan.

[jsterck]

Thanks for the update.. I will test the config changes tonight and post back any results I have..  Thank you!

Jeff