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Archive for September, 2015

Ran into an interesting issue the other day.  A customer was trying to run an application called AirServer in their environment.  AirServer extends Apple’s wireless Airplay feature to wired devices.  By default, AirServer works only on one subnet, so wired and wireless users must be in the same IP subnet.  By using the Bonjour service, AirServer can extend Airplay across multiple IP segments.

AirServer is installed on target desktops and laptops, which then send video streams to client devices (iPads and iPhones) using multicast addresses in the 239.0.208.0/24 range.  It also uses mDNS to advertise server names to the clients.  The customer’s network infrastructure, both wired and wireless, is built using only Cisco devices, particularly WLC5508s for the wireless controllers.

The issue we rant into was this: after configuring PIM and IGMP on the layer 3 and 2 devices respectively, and enabling multicast and IGMP snooping on the WLCs, the clients could not see the servers.  We could see the mroutes in the table and the members in the IGMP table, but the multicast streams never got beyond  the core layer 3 switch.

After a lot of troubleshooting and a couple of go-rounds with Cisco TAC, we stumbled on the solution.  Because the multicast streams are not sourced from the wireless environment, all of the wired VLANs had to be trunked to the WLC5508s, after which SVIs had to be created on the WLCs for each of the wired VLANs.  Once we did that, everything worked like a charm.

My guess at the root cause is that the WLCs do not snoop IGMP traffic on the trunk links, so they never took the multicast streams in to send out to the wireless clients.  If anyone out there can confirm or correct that, I’d appreciate it.

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