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7910 intermittent DHCP problem


I'm having a problem with the 7910 phones getting the correct IP information from the DHCP server. The switch (cat4006) is set up with auxiliaryvlan 3 for the phones and vlan 2 for data. I have DHCP scopes created for each vlan. When I put a phone on the network it will often get an Address from the data vlan (vlan 2) although the Operational VLAN shows correctly as 3 in the network properties. The phone will look for the call manager list for a minute and then reboot. It does this maybe 5-15 times and then eventually gets the right information. If I release the address on the phone and delete the reservation on the server enough times it will eventually come up also.

The problem seems to only be affecting 7910 phones that hang of the core 4006 switch. I have not seen the problem in remote closests.

My config for the powered port blades in the 4006 specifies auxiliary vlan 3, port channel off, trunking off and portfast on.

The DHCP server is an NT 4 sp 6 box.

Any ideas would be appreciated.

Community Member

Re: 7910 intermittent DHCP problem

You require trunking as the Cat will only read the .1Q headers if trunking is on

Community Member

Re: 7910 intermittent DHCP problem

That's interesting. I was told I didn't need trunking on when using auxiliary vlans. I'll try that and see if it helps.


Community Member

Re: 7910 intermittent DHCP problem

Same problem with 7940 at a 3524-PWR-XL port.

Phone will get an DHCP reply from an DHCP server within the data VLAN, which is the native VLAN

on the dot1q-trunk to the phone. It seems that

the phone is not only sending DHCP request on the voice VLAN, but also on the data/native VLAN.

So the phone gets an address which fits in the address space of the data vlan. An address with about

no chances to make friends with in the voice vlan....

After a while (about 60 sec) the phone gives up and

checks for the other DHCP-server in the voice vlan and will finally get a correct address with which

contacting the CM is easy.

Have a case open on that.


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