Can one connect an unmanaged switch or hub to a 7965 phone's access port

CHRISTINE BERNS · ‎01-07-2009

Is it OK to connect a switch or hub to a phone's access port to accommodate multiple PCs hanging off the phone? It was my understanding that a VoIP phone had an internal 3-port mac-address table, accommodating the mac-address of a single PC, the mac address of the phone, and some sort of an internal mac address. So more than one PC hanging off the phone could not be accommodated. A consultant is telling us that you can indeed drop multiple PCs off the phone via a hub or switch, but I am not convinced of this. Anyone have any thoughts on this?

Rob Huffman · ‎01-08-2009

Hi Christine,

It may work with a Switch and PC's only, but I wouldn't do it and I'm sure this would not be considered a "Best Practice" just like you most correctly noted. The IP Phone with PC is meant to be a one to one realationship. Here is some additional info that reflects the fact that Daisy Chaining IP Phones is not supported (it does not specify PC's but......);

Daisy Chaining Cisco Unified IP Phones

Cisco does not support connecting an IP phone to another IP phone through the PC port. Each IP phone should directly connect to a switch port. If phones are connected together in a line (daisy chaining by using the PC port), the phones will not work.

http://www.cisco.com/en/US/docs/voice_ip_comm/cuipph/firmware/8_3_4/english/release/notes/79xx_834.html#wp148809

Here is another similar post;

http://forum.cisco.com/eforum/servlet/NetProf?page=netprof&forum=Network%20Infrastructure&topic=Getting%20Started%20with%20LANs&CommCmd=MB%3Fcmd%3Dpass_through%26location%3Doutline%40%5E1%40%40.1ddaf45c/0#selected_message

Hope this helps!

Rob

steve.bowers · ‎01-09-2009

Hi,

We've got several phones running in this manner successfully.

Whether it's a Cisco supported configuration or not, I don't know.

Edit: Our phones are all 7945/65G handsets. It's possible that some of the older / lower models may not work in quite the same way.

Nicholas Matthews · ‎01-09-2009

This will work in theory. You may run into problems with a higher number of phones behind the hub (high traffic), and if STP messages may get passed through the switch, or if you run multiple IP communicators behind the phone on PCs.

It's not a supported configuration. There have been issues with the switch on the phone becoming too busy moving switched traffic to operate normally, and there were registration/voice problems because of this. This is one of the reasons the physical layout is not supported.

You can probably do it, but I wouldn't depend on it in a system design.

hth,

nick