Solved: IGMP snoop not working catalyst 3560?

camber_shill · ‎02-16-2010

reguardless of whether i turn snooping on or off (vi

a network assistant) multicast packets are being switched to all ports

on the VLAN). I thought if snooping was enabled it would only forward to those ports that had made request

s to join the same multicast group. eg. 226.0.201.

1 is seeing the traffic from 226.0.202.1 and vice versa.

Jon Marshall · ‎02-16-2010

camber_shill wrote:

reguardless of whether i turn snooping on or off (vi

a network assistant) multicast packets are being switched to all ports

on the VLAN). I thought if snooping was enabled it would only forward to those ports that had made request

s to join the same multicast group. eg. 226.0.201.

1 is seeing the traffic from 226.0.202.1 and vice versa.

Scott

Lei's answer is what you need to do. Just to expand on the point. IGMP snooping allows the switch to listen to responses to IGMP queries and record those in it's cam tables. For IGMP snooping to work something must be making the IGMP queries because IGMP snooping is passive in that sense ie. it listens but it can't make the queries itself.

So you have 2 options -

1) enable PIM on the L3 vlan interface and this automatically enables IGMP queries

2) if you don't want to do that then you can enable the IGMP snooping querier function as Lei pointed out although not all switches support this function. This function does exactly what it sounds like it should do ie. it generates IGMP queries so that IGMP snooping can listen to the answers.

Jon

View solution in original post

Lei Tian · ‎02-16-2010

Hi Scott,

Are you doing multicast in a L2 only environment?

If yes, did you configure igmp snooping querier on the switch? See the link for configuration.

http://www.ciscosystems.com/en/US/docs/switches/lan/catalyst3560/software/release/12.2_25_see/configuration/guide/swigmp.html#wp1193337

HTH,

Lei Tian

Jon Marshall · ‎02-16-2010

camber_shill wrote:

reguardless of whether i turn snooping on or off (vi

a network assistant) multicast packets are being switched to all ports

on the VLAN). I thought if snooping was enabled it would only forward to those ports that had made request

s to join the same multicast group. eg. 226.0.201.

1 is seeing the traffic from 226.0.202.1 and vice versa.

Scott

Lei's answer is what you need to do. Just to expand on the point. IGMP snooping allows the switch to listen to responses to IGMP queries and record those in it's cam tables. For IGMP snooping to work something must be making the IGMP queries because IGMP snooping is passive in that sense ie. it listens but it can't make the queries itself.

So you have 2 options -

1) enable PIM on the L3 vlan interface and this automatically enables IGMP queries

2) if you don't want to do that then you can enable the IGMP snooping querier function as Lei pointed out although not all switches support this function. This function does exactly what it sounds like it should do ie. it generates IGMP queries so that IGMP snooping can listen to the answers.

Jon

camber_shill · ‎02-16-2010

I am confused.

should the table not be blank to start with and then entries only added when it sees requests from hosts to join the group? I do not need/want a querier to generate requests. only to listen.

Jon Marshall · ‎02-16-2010

camber_shill wrote:

I am confused.

should the table not be blank to start with and then entries only added when it sees requests from hosts to join the group? I do not need/want a querier to generate requests. only to listen.

Scott

Hosts don't make queries they use joins and leaves with IGMP. Routers or more specifically L3 interfaces running PIM make IGMP queries on the local subnet and it is this that IGMP snooping listens to the answers for.

Jon

camber_shill · ‎02-16-2010

I tried to enable it but it came back with "IGMP Queier functions cannot be

operationally enabled on some VLANS becase the required conditions have not been met"

how do i enable PIM on the VLAN or what condition am i missing?

Jon Marshall · ‎02-16-2010

camber_shill wrote:

I tried to enable it but it came back with "IGMP Queier functions cannot be

operationally enabled on some VLANS becase the required conditions have not been met"

how do i enable PIM on the VLAN or what condition am i missing?

Scott

Is there an IP configured on the vlan interface ie. the L3 SVI ? Do you have any L3 SVIs for that matter ?

Jon

camber_shill · ‎02-16-2010

even though it reported an error it is now working! thanks much.

if you have any ideas on my issue with multicast fragmented packets i would really appreciate it.

this was an annoyance but the other is killing application performance.