ACK for successull response is a new transaction. It has to be different. May be it is better to point provider to this?  On Mon, 10 Feb 2020, 14:26 Sebastian Damm, &lt;damm(a)sipgate.de <mailto:damm@sipgate.de>> wrote: Hi, I stumbled upon an interop problem with a carrier. We have the following scenario: Gateway --> Loadbalancer --> Carrier The loadbalancer generates a Via header for each request. But since it is stateless, the Via tag is generated for each request. As a consequence, the Via tag in the ACK differs from the one in the INVITE. And one carrier doesn't handle those ACKs if the Via tag differs. Is there a way to force the creation of a "deterministic" Via branch tag? For example, building it from a hash over call-id and from-tag or something like that? Thanks in advance Sebastian -- Sebastian Damm Voice Engineer __________________________________________ sipgate GmbH _______________________________________________ Kamailio (SER) - Users Mailing List sr-users(a)lists.kamailio.org <mailto:sr-users@lists.kamailio.org> https://lists.kamailio.org/cgi-bin/mailman/listinfo/sr-users _______________________________________________ Kamailio (SER) - Users Mailing List sr-users(a)lists.kamailio.org https://lists.kamailio.org/cgi-bin/mailman/listinfo/sr-users

Hi, actually, our only problem is handling negative replies. The ACK belongs to the same transaction and therefore has to carry the same Via branch ID. Sebastian On Mon, Feb 10, 2020 at 3:50 PM Yuriy Gorlichenko &lt;ovoshlook(a)gmail.com&gt; wrote: -- Sebastian Damm Voice Engineer __________________________________________ sipgate GmbH _______________________________________________ Kamailio (SER) - Users Mailing List sr-users(a)lists.kamailio.org https://lists.kamailio.org/cgi-bin/mailman/listinfo/sr-users

We use 5.2 on the affected systems. On Mon, Feb 10, 2020 at 4:15 PM Serge S. Yuriev &lt;me(a)nevian.org&gt; wrote:

In such case, because the proxy is doing stateless forwarding, there is no transaction. I guess the solution right now is to use tm for relaying - is any concern of doing that? If someone wants to look at generating same via branch, I am fine with it, eventually controlled by a parameter if the code change is significant, to be able to switch to current mode if unexpected side effects pop up. One more note in this case: I expect it would be required to generate different tag for 200ok ACK, so it is matched as different transaction by next hop, not sure if there is any easy way to discover the type of ACK in a stateless proxy. I am not sure I remember correctly, but in some discussions I think it was suggested to just reuse the branch value of incoming top Via when doing stateless forwarding. Cheers, Daniel On 10.02.20 16:26, Sebastian Damm wrote: >  We use 5.2 on the affected systems. > >  On Mon, Feb 10, 2020 at 4:15 PM Serge S. Yuriev &lt;me(a)nevian.org&gt; wrote: >>  Hi >> >>  I believe you are using 5.2 or 5.3 series? This tend to work >> properly on 5.1 series >> >>  10.02.2020, 18:10, "Sebastian Damm" &lt;damm(a)sipgate.de&gt;de>: >>>  Hi, >>> >>>  actually, our only problem is handling negative replies. The ACK >>>  belongs to the same transaction and therefore has to carry the >>> same >>>  Via branch ID. >>> >>>  Sebastian >>> >>>  On Mon, Feb 10, 2020 at 3:50 PM Yuriy Gorlichenko &lt;ovoshlook(a)gmail.com&gt; wrote: >>>>   ACK for successull response is a new transaction. It has to be different. May be it is better to point provider to this? >>>> >>>>   On Mon, 10 Feb 2020, 14:26 Sebastian Damm, &lt;damm(a)sipgate.de&gt; wrote: >>>>>   Hi, >>>>> >>>>>   I stumbled upon an interop problem with a carrier. We have the >>>>>   following scenario: >>>>> >>>>>   Gateway --> Loadbalancer --> Carrier >>>>> >>>>>   The loadbalancer generates a Via header for each request. But >>>>> since it >>>>>   is stateless, the Via tag is generated for each request. As a >>>>>   consequence, the Via tag in the ACK differs from the one in the >>>>>   INVITE. And one carrier doesn't handle those ACKs if the Via >>>>> tag >>>>>   differs. >>>>> >>>>>   Is there a way to force the creation of a "deterministic" Via >>>>> branch >>>>>   tag? For example, building it from a hash over call-id and >>>>> from-tag or >>>>>   something like that?

Hi all, thanks for the discussion and reminding everyone that it is already fixed. Henning, I guess we owe you a beer or two at Kamailioworld. :) Daniel, to answer your question regarding "why stateless": Our setup includes anycast, so multiple machines share the same IP address. And depending on the datacenter location of our gateways or the uplink to the carrier, even requests and answers can be routed through different instances running with the same IP address. So yes, even in 2020 there can be use cases for a stateless loadbalancer. We were running 5.2.2, and after I upgraded to 5.2.6, our error reply counter dropped significantly. Wow. Regards, Sebastian On Mon, Feb 10, 2020 at 8:02 PM Henning Westerholt &lt;hw(a)skalatan.de&gt; wrote: wrong refactoring. This were not noticed for some time because only a few people (still) use stateless load balancers. I noticed it as well in middle of last year during a customer project. It was fixed in 82635674517 end of July 2019, you find in the related discussion also some test results that I posted before doing the backport. So, if this is your problem, after 5.2.4 is should work again. S.Yuriev loadbalancer 5.2.1 already broken IIRC. wrote: ovoshlook(a)gmail.com&gt; wrote: different. May be it is better to point provider to this? wrote: -- Sebastian Damm Voice Engineer __________________________________________ sipgate GmbH _______________________________________________ Kamailio (SER) - Users Mailing List sr-users(a)lists.kamailio.org https://lists.kamailio.org/cgi-bin/mailman/listinfo/sr-users