[asterisk-dev] PJSIP internal DNS client binding to random sticky ports can look scary

[Joshua C. Colp]

On Fri, Dec 15, 2023 at 5:26 PM C. Maj <chris at penguinpbx.com> wrote:

> Howdy,
>
> This came up on the forums and seems appropriate to cross-post to -dev:
>
> https://community.asterisk.org/t/asterisk-listens-on-ipv6-port/99666
>
> OP wrote:
>
> "Please tell me why asterisk listens to ipv6 interface on random udp
> ports? Which module should be disabled or configured so that asterisk
> does not do this?"
>
> Reply mentioned previous discussion:
>
> https://issues-archive.asterisk.org/ASTERISK-25481
>
> Point of concern is in PJSIP pjlib-util resolver:
>
>
> https://github.com/pjsip/pjproject/blob/master/pjlib-util/src/pjlib-util/resolver.c
>
> Curious if best fix should be placed in third-party/pjproject/patches/
> to address the particular pj_sock_bind_in() functions, allowing both
> user-adjustable client binding host and port in /etc/asterisk/pjsip.conf
> with appropriate documentation around these new options ?
>
> Or, would a more developmentally-complicated *but
> less-anxiety-inducing-for-end-users* fix involve opening and closing a
> socket *as needed* ?
>

Modern versions of Asterisk don't use the PJSIP resolver. We replace it
with our own callback in res/res_pjsip/pjsip_resolver.c and do it on our
own using either res_resolver_system, or res_resolver_unbound (which would
listen itself). If PJSIP is still listening for DNS responses, then that
would most likely be a bug and a patch to disable it when an external
resolver (in PJSIP speak) is used should be provided to Teluu on their
GitHub to see what they think, and then backported.

-- 
Joshua C. Colp
Asterisk Project Lead
Sangoma Technologies
Check us out at www.sangoma.com and www.asterisk.org
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