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Cisco IP phone connected to 3COM switches


Only to confirm if I didn't missed something. My customer is looking to use somes of their existing 3COM switches for their light Wire Closet (ex: less than 5 Ip Phone and few PC). Those 3COM will be directly connect to Cisco 3524/3550 switches.

I have tested the dynamic vlan assignment using CDP protocol since CDP packets are multicast, they will be coming from the Cisco switch and then flood on the 3COM switch. The only special setup is to define the IP phone port on 3COM switch using vlan 1 as untagged (since CDP are always send as a tagged Vlan1 packet upon trunk). Also on those Ip phone 3COM port - voice vlan should be defined as tagged.

I have tested that setup with 3 phones without any problem - but I was wondering if increasing those phone number could lead to some problem. For example could it happen that phone will freak down (CDP table overflow, etc ...) seeing to much IP phone like neighbor. Remember CDP packets will be flood, so the Cisco switch and all the IP phone sitting on the 3COM switch will see them as CDP neighbors.

Please share experience where you are also using also CDP Vlan assignment using a third party switch connect to a Cisco Sw.

Thanks - sorry for the long story !


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