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mysterious behavior of IP phone

I have two scenarios, one works, the other doesn't work. Cannot figure out why.

Scenario 1:

Catalyst2950---NonCisco Switch---7960 Phone---PC.

Scenario 2:

Catalyst2950---7960 Phone---PC.

1 works, 2 doesn't work.

The catalyst2950 has default settings (which means I cleared all config and restarted the switch).

The NonCisco switich is a 8-port Airlink switch I got from Frys for $2.

In two scenarios, I connected to the same port on the catalyst2905. The PC was connected to the back of 7960 phone.

Thanks in advance.


Re: mysterious behavior of IP phone

in scenario 2, neither IP phone nor PC can get IP address from DHCP.

in scenario 1, both can get IP addresses.

New Member

Re: mysterious behavior of IP phone

Try Turning on Portfast on the switchport.

Spanning-tree portfast

Re: mysterious behavior of IP phone

set your port for dot1p:

switchport voice vlan dot1p

Re: mysterious behavior of IP phone

Posting the configuration of the 2950 would help. If the 2950 is configured with a Voice Vlan it's more than likely going to be untagged when it comes through the NonCisco Switch at the cost you paid for it. Just because it's a switch doesn't mean it participates in 802.1q.

With that being said probably the voice vlan probably isn't configured correctly at it's L3 interface with the corresponding DHCP helper address. So when going through the cheap switch it's stripping the vlan tag and everything is untagged coming back into the 2950. Thus you are probably getting a DHCP on your phone on the PC vlan (switchport access). Check to see if your PC and Phone are receiving the same subnet from DHCP.

Additionally ACLs could be applied on your L3 interfaces for your Voice Vlans preventing DHCP. But more than likely DHCP scope setup overall or Helper-address configuration on the L3 interface is the issue.



New Member

Re: mysterious behavior of IP phone

In scenario 2, if you issue a show cdp neighbors in the 2950, can you see your phone?



New Member

Re: mysterious behavior of IP phone

Check that your port hasn't gone into an err-disable state. I know that on some non inline power switches, the ports shutdown when you plug a phone in. Do a shut, no shut on the port to bring it back online.

I think there's a workaround for the issue outside of a port shutdown, but can't remember it at this point.

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