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Strange ARP reply on cisco IP Phone 7940


I have a strange problem with cisco phones 7940 model software version P0M3-07-06-00

For some reason these phones while connected to a linksys switch stop sending arp replys in the correct vlan in which they were recieved. For example the phone recieves arp requests tagged with vlan 101 and replys to those request with arp reply packets tagged wtih id 101 but sometimes the phone would stop tagging these replys and they would end up in the native vlan. For some reason the phone would start sending replys in the correct vlan after some time of recieveing arp request and sending non tagged replys.

These phones are using a router as their GW which has an arp chache timeout of 30-40 seconds. When the entry times out the router sends arp requests over tagged 101 vlan and when they are answered by the phone tagged with the correct vlan in which they were recieved all is working well, the router rests the arp chache timer. But when the phone starts answering requests with them untagged the router doesnt reviece an arp reply in the correct vlan (101) in which he sent it and removes the entry. This causes the router to stop forwarding the rtp stream untill the phone answers with a tagged reply. This lasts for about 3-10 seconds.

The port is configured as two vlan trunk(linksys general port) with 101 tagged and 100 native vlan.

Has anybody seen a similar behaviour with a cisco IP Phone?

2 Replies 2

paolo bevilacqua
Hall of Fame Master Hall of Fame Master
Hall of Fame Master

Try updating phone firmware. The one you're using is very old.

Thanks for the suggestion i will try updating the firmware.

Altho i must note that we have not seen this problem with this firmware in other setups. When the phones are connected to cisco switches they seem to be working properly so i was wondering if this is a bug of some sort. Firmware update might answer this question.

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