We have a 3560 Switch as a core Switch, and I connected a 3550XL Switch to the core Switch. On our 3560 Core Switch we have lots of server including a CallManager server. Everything is working fine except when I will connect an IP Phone on the 3550 Switch, it can't see our Call Manager server.
Hope you can help guys. Thanks.
for the old XL series, you must configure trunk to ipphone, and then do voice vlan. I do not think trunk negotiation is supported.
you can confirm when you do "sh int fax/y switchport" and look for voice vlan.