asterisk users - Feb 2015 - IAX port

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
t: +44 (0)845 004 4994
f: +44 (0)161 660 9825
e: ish at pack-net.co.uk
w: http://www.pack-net.co.uk

Registered Address: PACKNET LIMITED, Duplex 2, Ducie House
37 Ducie Street
Manchester, M1 2JW
COMPANY REG NO. 04920552
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>
> Some firewalls have a 'consistent NAT' option that needs to be
enabled, otherwise you get the
> symptoms described.
>
While reading about NAT, I came across this web site:
http://nattest.net.in.tum.de/
The test tool looks at various NAT related properties and prints the results
related to TCP/UDP
binding properties, TCP/UDP hole punching, etc.

In my case a very short value was reported for the UDP timeout, such that
depending on the
sequence of packets, the entry in the mapping table might already have been
deleted. This could
explain the random nature of my  connection problem. Port predictability does
not seem to be a
problem.

Does that make any sense?
jg

On 10 February 2015 at 12:55, jg <webaccounts173 at jgoettgens.de> wrote:
>
>> Some firewalls have a 'consistent NAT' option that needs to be
enabled,
>> otherwise you get the symptoms described.
>>
>>  While reading about NAT, I came across this web site:
> http://nattest.net.in.tum.de/
> The test tool looks at various NAT related properties and prints the
> results related to TCP/UDP binding properties, TCP/UDP hole punching, etc.
>
> In my case a very short value was reported for the UDP timeout, such that
> depending on the sequence of packets, the entry in the mapping table might
> already have been deleted. This could explain the random nature of my
> connection problem. Port predictability does not seem to be a problem.
>
> Does that make any sense?
>
> jg
>
>
Yes

UDP timeout being too short is another thing I've experience with firewalls
(admittedly limited and once removed experience). Actually, this one can be
a (mild) problem on Draytek routers and can be resolved by telnetting into
the router and using the portmaptime command.

Also, turn of stateful packet inspection if it is an option.


-- 

Ishfaq Malik
Department: VOIP Support
Company: Packnet Limited
t: +44 (0)845 004 4994
f: +44 (0)161 660 9825
e: ish at pack-net.co.uk
w: http://www.pack-net.co.uk

Registered Address: PACKNET LIMITED, Duplex 2, Ducie House
37 Ducie Street
Manchester, M1 2JW
COMPANY REG NO. 04920552
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