Multicast streaming filtered on the PC Port of a Cisco Phone

[Gianstefano Monni]

Dear all,

in our Campus network we have a working multicast implementation with IGMP/PIM sparse mode.

The clients are able to receive multicast streams, but when we connect the client to the network through a Phone (on the same Switch port), both the phone and the PC work as expected (on two different vlans, etc) but the client doesn't receive the streaming anymore. It looks like that the onboard switch of the cisco phone is filtering the IGMP and/or the multicast packets.

We verified that if the PC is connected directly to the Switch port then the IGMP request flows and the mroute is created on the access switch (Cisco 4506), but when the same PC is connected to the same port through a Phone then the mroute is not created.

any help will be appreciated, thank you

stefano

[Gianstefano Monni]

We manage to make it work.
The issue was related to an ACL on the voice VLAN. Even if the phone doesn't need to receive the multicast stream (only the desktop behind the phone needs), in the ACL of the Voice VLAN should allow access to the multicast iP addresses. most likely this is needed because IGMP requests come from the onboard switch of the phone which has an IP address on the voice VLAN.