We have a device that needs to communicate with it's other peers via multicast at bldg A,they are all on the same Cisco 4500 blade on the same vlan. This same device also needs to communicate with a server in a different vlan on a different vlan via unicast/tcp in Bldg B.
With this set up in mind I did not enable multicast on the interface vlan at bldg A b/c they are all on the same vlan. The vendor confirmed they could all talk to each other. We came back to Bldg B to set up the server and it and the primary device at bldg A could not communicate via unicast. I tested from Bldg B and could not ping the devices at A. I logged into the switch in Bldg A that they are directly connected to and was able to ping the devices. Once I did that they were reachable from Bldg B for about a minute then they would stop replying again.
This was the case every time I pinged local to the devices. Finally I enabled PIM sparse-dense-mode on the interface vlan these multicast devices shared at Bldg A and they were pingable, the server could communicate with it's unicast TCP traffic.
WTF? Multicast configuration should have no bearing on ICMP or unicast traffic. Why did this make a difference?
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