[sr-dev] [SR-Users] bug ? remap_503_500 breaks dialogs

[M S]

The SIP code 503 is tricky in the sense that i can indicate either server
maintenance or server overload. In both cases it can send Retry-After
header and any subsequent requests from same source are ignored for the
duration of Retry-After interval. [1].

Additionally RFC3261 and RFC3263 define that transport failures (generally
due to fatal ICMP errors in UDP and connection failures in TCP) should be
treated as 503 response. [2].

So in all above cases, it is most likely that dialog does not establishes
at all and 503 response is treated similar to stateless response.
Therefore, a to-tag can be added/replaced before sending it to UAC.

Theoretically, kamailio should check and use to-tag from 503 response when
converting it to 500 response and only create new to-tag if it is absent.

References:

[1] https://tools.ietf.org/html/rfc3261#section-21.5.4

[2] https://tools.ietf.org/html/draft-hilt-sip-correction-503-01#section-4


Hope this helps.



On Wed, 22 Jul 2020 at 21:08, Henning Westerholt <hw at skalatan.de> wrote:

> Hello,
>
>
>
> Apparently, this is the way the code works:
>
>
>
> t_reply.c:
>
>                         if (relayed_code==503 && tm_remap_503_500){
>
>                                 /* replace a final 503 with a 500:
>
>                                  * generate a "FAKE" reply and a new
> to_tag (for easier
>
>                                  *  debugging)*/
>
>
>
> Lets see if maybe others can comment as well. Otherwise you could just
> open an issue on our tracker, it is probably not that hard to change this.
>
>
>
> Cheers,
>
>
>
> Henning
>
>
>
> --
>
> Henning Westerholt – https://skalatan.de/blog/
>
> Kamailio services – https://gilawa.com
>
>
>
> *From:* sr-users <sr-users-bounces at lists.kamailio.org> *On Behalf Of *Gerry
> | Rigatta
> *Sent:* Wednesday, July 22, 2020 8:58 PM
> *To:* Kamailio (SER) - Users Mailing List <sr-users at lists.kamailio.org>
> *Subject:* [SR-Users] bug ? remap_503_500 breaks dialogs
>
>
>
> Hi,
>
>
>
> I am using Kamailio 5.2.
>
>
>
> Apparently the remapping of 503 to 500 codes in the tm module does also
> change the to-tag. This behaviour breaks dialogs with yate and therefore
> calls hang and the 503 remains unacknowledged. After disabling the 503 to
> 500 remapping with modparam("tm", "remap_503_500", 0) all works fine again.
>
>
>
> Changing the to-tag in a dialog seems to contradict RFC3261, or do I see
> this wrongly?
> 12 <https://tools.ietf.org/html/rfc3261#section-12> Dialogs A dialog is
> identified at each UA with a dialog ID, which consists of a Call-ID value,
> a local tag and a remote tag…"
>
>
>
> Thanks for looking into this.
>
>
>
> Gerry
>
>
> _______________________________________________
> Kamailio (SER) - Users Mailing List
> sr-users at lists.kamailio.org
> https://lists.kamailio.org/cgi-bin/mailman/listinfo/sr-users
>
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