[SR-Users] Negative ACK issue
Daniel-Constantin Mierla
miconda at gmail.com
Tue Jan 14 10:20:43 CET 2020
Curious about the ALG vendor/model/version, if it is some
carrier/enterprise grade firewall, just to be aware when meeting it ...
of course, if you can and want to share such details...
Cheers,
Daniel
On 14.01.20 08:42, Lợi Đặng wrote:
> Nice, be ware of the ALG, sometimes it's an unpredictable foe.
>
> rgds,
> Loi Dang Thanh
>
>
> On Tue, Jan 14, 2020 at 4:42 AM Michael Broughton
> <mbroughton at advanis.net <mailto:mbroughton at advanis.net>> wrote:
>
> Just to provide some closure to this, the problem did end up being
> with the Via headers and our firewall ALG.
>
> In the top Via header of the INVITE requests the ALG was
> transforming the internal proxy address to our external address
> and adding port 5060. In subsequent negative ACK and CANCEL
> requests, the ALG was transforming the internal proxy address to
> our external address with no port number. Thus the Via's did not
> exactly match, and this prevented our telco from matching the
> existing transaction.
>
> I was able to fix the issue by modifying our Kam config with the
> advertise parameter:
>
> listen = 10.x.y.z advertise 10.x.y.z:5060
>
> With this setting in place the ALG is forced to behave itself.
>
>
>
> On Thu, Jan 9, 2020 at 9:27 AM Michael Broughton
> <mbroughton at advanis.net <mailto:mbroughton at advanis.net>> wrote:
>
> I'm using 5.3.1+stretch from deb.kamailio.org
> <http://deb.kamailio.org> for our new setup. Our old setup was
> using 4.4.4+wheezy.
>
> On Thu, Jan 9, 2020 at 9:16 AM Daniel-Constantin Mierla
> <miconda at gmail.com <mailto:miconda at gmail.com>> wrote:
>
> Is it a recent version of kamailio, or an older one?
>
> Cheers,
> Daniel
>
> On 09.01.20 16:55, Michael Broughton wrote:
>> Thank you, this was a helpful sanity check.
>>
>> We have been capturing SIP traces to try and debug this.
>> I normally just look at the traffic on our Kam box
>> because it is convenient to do so, but I have also taken
>> traces on our firewall to check the ALG behaviour. The
>> provider techs are also tracing these calls on their
>> network as well. The ALG is new equipment in our setup,
>> but as far as I can tell it is behaving correctly.
>>
>> The one rather annoying discovery that I made is that
>> when I call directly out from the source (Freeswitch in
>> this case) and bypass Kamailio, the negative ACK's seem
>> to work. I do not see any retransmissions of their final
>> response. And of course the only significant difference
>> in the SIP traces is the Via headers.
>>
>> Anyway, thanks again for your input.
>>
>>
>> On Thu, Jan 9, 2020 at 4:04 AM Lợi Đặng
>> <loi.dangthanh at gmail.com
>> <mailto:loi.dangthanh at gmail.com>> wrote:
>>
>> Hi,
>> You're not going to have the Via header from your
>> `source` sent to your `telco provider` in the
>> negative ACK when the call is not answered, because
>> the ACK in the right hand side of the call is created
>> by the kamailio itself, not a forwarding one by the
>> `source`.
>> Yes, you've guessed it, ACK for an answered call is a
>> forwarding one which contains all the Via headers.
>> It's the SIP spec, not kamailio, you may want to dive
>> into rfc3261 for more details.
>>
>> In this case, your telco's expectation is not
>> correct, my best guess is something went wrong with
>> either your SIP ALG or Telco Provider. SIP capturing
>> may help.
>>
>> rgds,
>> Loi Dang Thanh
>> Phone : +84. 774.735.448
>> Email : loi.dangthanh at gmail.com
>> <mailto:loi.dangthanh at gmail.com>
>>
>>
>> On Thu, Jan 9, 2020 at 2:42 AM Michael Broughton
>> <mbroughton at advanis.net
>> <mailto:mbroughton at advanis.net>> wrote:
>>
>> Hello,
>>
>> Long time Kam/Ser user, first time poster.
>>
>> I'm running into a problem with one of our
>> telco providers when we make a call that ends up
>> being not in service or some other error. In
>> this case our ACK's are not working and the phone
>> line stays open for a period of time
>> until something times out on their end.
>>
>> They claim the issue is that our negative ACK
>> message is dropping one of the Via headers. This
>> is the only case I can find in our setup where
>> Kamailio does this. But it does drop the first
>> Via, which is the first hop in our internal network.
>>
>> I don't understand why this is a problem for
>> them, and I'm still trying to get a reasonable
>> explanation out of them. Technically, I don't see
>> why it would be a problem. This behaviour is not
>> an issue with our other telco providers.
>> Strangely enough, it is also not an issue for
>> this provider when we make the calls over their
>> MPLS network (we are switching to the internet).
>>
>> My question is, can this behaviour be changed in
>> Kamailio somehow? Is there a way for it to keep
>> all the Via headers for negative ACK's?
>>
>> Or, do I just need to poke them harder to fix
>> their issues?
>>
>> My setup:
>>
>> Source -> Kamailio -> Firewall (NAT, SIP ALG) ->
>> Telco Provider
>>
>> I hope I have provided enough information.
>>
>> Thanks!
>> Michael
>>
>>
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> --
> Daniel-Constantin Mierla -- www.asipto.com <http://www.asipto.com>
> www.twitter.com/miconda <http://www.twitter.com/miconda> -- www.linkedin.com/in/miconda <http://www.linkedin.com/in/miconda>
> Kamailio World Conference - April 27-29, 2020, in Berlin -- www.kamailioworld.com <http://www.kamailioworld.com>
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Daniel-Constantin Mierla -- www.asipto.com
www.twitter.com/miconda -- www.linkedin.com/in/miconda
Kamailio World Conference - April 27-29, 2020, in Berlin -- www.kamailioworld.com
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