[Asterisk-Users] Cisco 7940/7960 ethernet ports

[Rich Adamson]

> [...]
> > We are having a problem with Cisco 7940 and 7960 phones when 
> > the PC is plugged into the 2nd ethernet port on the phone. It 
> > will drop the PC's connection for about 30 seconds, then 
> > bring the connection back up for about 30 seconds. It does 
> > this continually regardless of how the port is configured on 
> > the phone.
> [...]
> 
> Sounds like failing autonegotiation.  Lock it down to a speed an duplex
> on the phone as well as on the device attached to the phone.

We're running a pair of C7960's v4.4 and we're not seeing that problem at
all, although I've heard others mention the problem.

A quick check with a real sniffer indicates the 7960 functions purely as
a hub (not a switch) for the attached pc. The sniffer also pointed out
that the 7960 is participating in Cisco Discovery Protocol (CDP), and the
packets are being passed through a 3Com switch to a Cisco router. The Cisco
router (in our case) is complaining about full vs half duplex, etc, relative
to the phones. (If the 3Com switch were supporting multicast, I wouldn't
think the CDP packets would get through the switch.)

Given that a switch's spanning tree disables port-forwarding for 30 seconds
following a link insertion, I'd have to believe the issue truly is the link 
dropping between the phone and the switch (possibly relating to CDP), and 
the switch is kicking in the 30-second spanning tree delay before forwarding 
packets. (If you're using vlans on your backbone, its also possible the 
phone is trying to discover the vlan to use and causing disruption. Disable
the vlan discovery on the phone to test it.)

If you have CDP in use, try disabling that on your cisco non-phone device(s)
to see what impact it has on the problem.