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Weird 1 Way Audio Traffic Issue between same VLAN

Hi there, i am having a weird 1 way audio issue at moment. We have several PoE switches in the same building which our Cisco IP 7940 phones have been working fine on for a while now.

At the weekend we had a lot of desk moves, during which there was some miss patching done which created a loop and Spanning-Tree Broadcast over our network. this was quickly noticed and patching resolved which in turn resolved the spanning-tree issue. The IP Phones came up and looked normal so nothing else was tested.....

Here's where the weird issue has come about. Now we have an issue where there are a number of IP phones (all on the same switch - the switch that was mispatched and caused the Spanning-tree broadcast) that when they initiate a call to any other IP phone in the same building, audio is 1 way (from initiator is OK).

Now, they can call any other IP phone on the same switch and 2 way audio is OK. they can also call mobile, outside numbers and IP Phones at other sites OK. More unusually they can receive calls from anywhere and 2 way audio is OK. It is only an issue when they initiate the call.

I have tried, resetting the IP phone, resetting the switch port etc with no luck. If i take a troubled IP phone and patch it into another switch, it is OK also.

I'm planning on power cycling the problematic switch and \or rebooting the publisher.

Can anyone help or have come across this before?


mark cummings


Re: Weird 1 Way Audio Traffic Issue between same VLAN

Did you try a SHOW PORT and look at the status of a working port on a working switch compared to a 1 way working port?

Cisco Employee

Re: Weird 1 Way Audio Traffic Issue between same VLAN

Hi Mark,

The path from Phone B to Phone A is broken - are these phones in the same local L3 subnet? Sounds like an L2 problem to me, I would start on the Phone B switch and look at the arp table to make sure it doesn't have any stale or leftover data.

Do you have L3 connectivity to the phones from elsewhere on that VLAN?(ping, phone web service, etc).

I'm assuming this isn't specific to UDP RTP packets, more that it's effectivy all connectivity.

I'm also assuming that your CallManager is off-site or in a different VLAN? Packets from the default gateway appear ok since you can reach off-site phones, CUCM, etc.

Good luck,


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