replacing 3com switches with cisco, non-cisco phone support

Unanswered Question
May 12th, 2008

We are replacing a 3com switch chassis with a 4500. The 3com allows us to set the port to "hybrid" to allow voice/data on the same port. Also, the 3com switch management software lets us do this automatically when a device is plugged in so we don't have to set each port manually. How can I accomplish this with cisco switches? I don't want to set all ports manually if I use non-cisco phones.

I have this problem too.
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l.mourits Mon, 05/12/2008 - 23:49

Could you specify your setup some more, since it is not clear from your dscription if you are using different vlans and subnets for vocie and data (would be good practice though).

If you are using different subnets and vlans the answer is simply "yes", the switch can determine voice and dat traffic and put it in different vlans.

Sample config:

interface FastEthernet

switchport access vlan

switchport mode access

switchport nonegotiate

switchport voice vlan

no logging event link-status

srr-queue bandwidth share 10 10 60 20

srr-queue bandwidth shape 10 0 0 0

priority-queue out

mls qos trust cos

no snmp trap link-status

auto qos voip trust

storm-control broadcast level 50.00

storm-control multicast level 50.00

storm-control unicast level 99.00

storm-control action trap

spanning-tree portfast

This config works with Avaya phones.



mfalcon818 Tue, 05/13/2008 - 05:42

Yes, we are using a different VLAN for voice and data on a 3com 7757 switch. Are you saying that with this setup, you never have to do anything more to have the phone or attached PC set into the proper vlan? How does the switch know if the device is a phone or not?

l.mourits Tue, 05/13/2008 - 05:53

How the switch determines if the device is a phone or not?

Simple answer, it does not!

Better answer, the switch determines by the vlan tag, and expects the phone to determine the vlan tag to be sued.

The command "switchport voice vlan" makes a Cisco switch to send out CDP messages. A Cisco IP phone will learn via this CDP messages what the voice vlan is, and tag traffic accordingly. All other traffic will default to non-tagged, and end up in the data vlan.

The config however also works with Avaya phones since they learn the vlan number via DHCP options.

It depends on your brand of IP phones and the way the phones learns the vlan weither or not it will work similar for you.

Maybe you can port your IP phones brand/model so I (or someone else) can point you into the right direction.

Bottom line, it is not the switch that determines the separation in the example I provided. It is supposed to be handled by the phone, where data equipment defaults to the data vlan. It is all about tagging the correct vlan tag.




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