Trunk ports with clients from 2 different vlan's

By mnicole.76 ·
I have a PC client connected to a IP phone which is in turn connected to a port of a cisco 2960 switch. Both PC and IP phone are to be in different vlan (e.g. 2 and 3 respectively). The port obviously has to be trunk since it serves both vlan 2 and 3. How do I configure so that, during a dhcp request, the switch knows that the PC belongs to vlan 2 and ip phone vlan 3? I know this has been done before but can't seem to google any useful information on the web.

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Voice VLAN

by NetMan1958 In reply to Trunk ports with clients ...

Try this on your switch:

SW2950(config-if)#switchport voice vlan ?
<1-4094> Vlan for voice traffic
dot1p Priority tagged on PVID
none Don't tell telephone about voice vlan
untagged Untagged on PVID

SW2950(config-if)#switchport voice vlan

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Sounds correct, but didn't work.

by mnicole.76 In reply to Also

Actually I'm using the AVAYA phone systems, not Cisco, so I wonder if this affects. My phone is unable to get a dhcp address at all after the "switchport voice vlan 3" command. I wonder if I did something wrong.

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Avaya Phones

by NetMan1958 In reply to Sounds correct, but didn' ...

I've never used Avaya phones so I had to research this. Take a look at this link:

Since this is a 2960, I don't think you will be able to configure an ip address on any vlan except the management vlan.

Also, I think that the "option 176" has to be modified according to the phone model, i.e.
if you are using the 4600IP phones, it should be option 176, if it's the 9600IP phones, it should be option 242.

You may need to research on Avaya for your particular model.

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Layer 3?

by Jellimonsta In reply to Trunk ports with clients ...

Is the 2960 a layer 3 switch? If is it simply layer 2, you will need to ensure the voice vlan on the layer 3 device has the appropriate ip-helper addresses. Or, if that layer 3 device is going to provide IP for the Avaya phones, it has the correct tftp option for the Avaya phones in the local IP pool.

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by -Q-240248 In reply to Trunk ports with clients ...

Make sure you have the scopes defined in DHCP. Then, when the dhcp server sees the source of the subnet where the DHCP request came from, it will give it an IP with that Mask of addresses.

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Dont forget to trunk

by melvin In reply to Trunk ports with clients ...

1.) make sure that you have the dynamic desirable trunk setting enabled.
2.) enable portfast
3.) Set up the voice vlan, ip helper and dhcp scope.

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avaya phones and cisco switch

by mnicole.76 In reply to Dont forget to trunk

thanks, melvin, this helped a bit. both the dynamic desireable trunk and switchport mode trunk worked. the problem is (i think!) cisco switch cannot understand the avaya phone cos the avaya phone does not understand cdp (cisco uses cdp to communicate between switchand cisco phone). but in the avaya phone i can enable 802.1Q and set vlan statically to vlan 3 - my voice vlan. that will make sure all traffic from the avaya is tagged to vlan 3. a PC connected to the phone is not tagged so traffic from the PC is treated as the default vlan of the port. In this way that one port on the switch is able to differentiate between the phone and PC traffic and assigns different vlan to both. Can't believe it's so simple and all this while I was searching for something complicated. Thanks to netman1958 too.

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