[asterisk-users] IAX port

Ishfaq Malik ish at pack-net.co.uk
Tue Feb 10 04:19:24 CST 2015

On 10 February 2015 at 09:02, jg <webaccounts173 at jgoettgens.de> wrote:

>> I get an occasional similar problem, we have Mikrotik firewalls and from
>> tcpdump monitoring on the asterisk boxes I can see that the firewall
>> (unbidden) has changed the IAX port. Usually a firewall reset and sometimes
>> PBX reset combination fixes it.
>> Its odd as its only one direction, occurs rarely and with no obvious
>> driver. So IAX is happy in one direction but not the other. And I can see
>> packets in the unhappy point arriving on the wrong port.
>> I couldn't fix it without kicking the router/firewall so I would say its
>> a router problem in the Destination NAT process.
>> Cheers Duncan
>>> Port is changed when NAT is applied from LAN to WAN.
>>> While UDP session is maintained as ESTABLISHED, that port should not
>>> change.
>>> If your peer changes constantly of session port could be UDP session
>>> is too short in NAT table on routers.
>>> You can try setting qualify=1000 (which is in ms. Default is 2000),
>>> and see if peer keeps same port.
>>> Regards.
>>>  voip-info.org also has an entry about general NAT related issues,
> which could be relevant here
> I do not seem to have problems with Netgear firewalls, but other firewalls
> show this effect. So far it happened only on a single side, such that calls
> work from the other side. I already checked the open ports with
> nc/ncat/netcat as UDP sender and receiver on the other end. The ports are
> open, even when the arbitrary ports are used by Asterisk.
> I'll need to read a bit more and evaluate my pcap traces and possibly ask
> the router vendors.
> Thank you for your efforts.
> jg
Some firewalls have a 'consistent NAT' option that needs to be enabled,
otherwise you get the symptoms described.


Ishfaq Malik
Department: VOIP Support
Company: Packnet Limited
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