[Asterisk-Users] Asterisk Netgear FSM7326P and Cisco 7960 on VLAN

[Ron Wellsted]

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Hi,

I have just finished a couple of very frustrating days trying to resolve
an issue with Asterisk 1.0.5, Netgear FSM7326P and Cisco 7960 phones
under SIP using a VLAN for the VoIP traffic.

The switch was configured with a default VLAN of 1 and the 7960s were
configured for a VLAN of 2.  The 7960s were tested with SIP firmware 7.3
and 7.4

The symptoms were as follows:
1/ When the phones were idle, every few minutes, the asterisk server
would loose MAC/IP address mapping for a phone.  Approx 10 seconds later
the mapping would reappear. (checked with "arp -avn")

2/ When in a call, we would randomly loose sound TO the phone.  Sound
FROM the phone was OK.  This loss would continue for about 10 seconds.

Using ethereal, we sniffed the traffic in and out of the Asterisk box
and saw that we were not getting replies to the targeted ARP packets
being sent from the asterisk box, only replies to the broadcast ARP packets.

Sniffing a phone revealed that although the ARP packets were correctly
tagged as VLAN 2, the phone was replying to the targeted ARP packets on
VLAN 1 (!?).  As a result the Asterisk box was (correctly) expiring the
arp cache entry when the ttl was reached, then it would send a broadcast
 ARP packet which would be responded to by the phone on VLAN 2.

I have worked around this be removing the VLANs and by using DHCP
reservations to put the phones on a different subnet from the rest of
the network.

Has anyone else found themselves in a similar situation?  If so, how did
you work around it?

Is it worth raising a TAC with Cisco?

- --
Ron Wellsted
http://www.wellsted.org.uk
ron at wellsted.org.uk
FWD:519961  Gossiptel:9309811
N 52.567623, W 2.137621
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