[asterisk-users] Losing local SIP phones when internet goes down?

[Nikhil Nair]

Hi,

I'm getting some strange behaviour on Asterisk 1.4 running on Debian 
Stable (Lenny).  I suspect it's something to do with my setup, rather than 
a bug, but I'm struggling to see it, and would appreciate any input.

Setup: PC with two ethernet cards: eth0 goes to local network, including 
two SIP phones (Aastra 9112i, wired, and Nokia E75, over WIFI); eth1 goes 
to router and thence to the internet over ADSL.  PC also has one Zap 
channel.

the SIP phones use DHCP but have defined IP addresses (DHCP server running 
on the PC).  The PC is also running a firewall (FIAIF), but not a DNS 
server.

Version of Debian Asterisk package: 1:1.4.21.2~dfsg-3+lenny1

Problem: When the internet connection goes down (which has been happening 
sporadically of late), connections to the two SIP phones on the local 
network get lost; ongoing calls from one of these phones over the Zap 
channel may get terminated, despite not using the internet.

I can reproduce this by switching off my ADSL router; however, if I simply 
take down the eth1 interface completely (by using "ifdown eth1", which 
executes "route del default gw ... eth1" and "ifconfig eth1 down"), the 
connections to the two SIP phones continue with no problems at all.

I enclose an extract from my sip.conf below.  Also, the logs indicate that 
Asterisk thinks the SIP phones are no longer reachable (ping timing out), 
while a manual ping from the same machine shows no trouble at all: the 
wired phone is responding in less than 2 ms each time, while the wireless 
one was a max of about 120 ms.

Any thoughts much appreciated!  Hopefully it's something obvious that I've 
overlooked...

Oh, BTW, the local phones are on a private net (10.9.8.xxx), but as it's 
the Asterisk box that's doing the NAT'ing, I used nat=no; I presume that's 
correct.  eth0 has address 10.9.8.1, while eth1 has a global internet IP 
address.

Cheers,

Nikhil.

-----

Extract from sip.conf:

[general]
context=incoming
srvlookup=yes
realm=nikhil-nair.net
; Various "register=>" statements, not relevant to the local phones

[101] ; Aastra 9112i at 10.9.8.101
type=friend 
secret=...
qualify=yes ; Qualify peer is no more than 2000 ms away 
nat=no ; This phone is not natted 
host=dynamic ; This device registers with us 
canreinvite=no ; Asterisk by default tries to redirect 
context=local
disallow=all
allow=alaw
allow=ulaw

[111] ; Nokia E75 via WIFI access point, at 10.9.8.111
type=friend 
secret=...
qualify=yes ; Qualify peer is no more than 2000 ms away 
nat=no ; This phone is not natted 
host=dynamic ; This device registers with us 
canreinvite=no ; Asterisk by default tries to redirect 
context=local
disallow=all
allow=alaw
allow=ulaw
allow=gsm