[SR-Users] Newbie: TOPOH in SBC/Proxy scenario regarding To-header

[Alex Balashov]

Proxies are absolutely not to alter the To and From header. If A sends a
request to B through proxy P, and P alters its To or From headers, those
get copied into responses and in-dialog requests from B back to A. 

A is well within its rights to say, "That's not my To header!"

Kamailio nevertheless has that capability:

   https://kamailio.org/docs/modules/5.1.x/modules/uac.html#uac.f.uac_replace_to

It is done in a "clever" way that allows it to conceal the fact that it
has been altered from A by restoring it to the original value in any
messages destined for A. You can learn more about that in the module
documentation, e.g.

   https://kamailio.org/docs/modules/5.1.x/modules/uac.html#uac.p.restore_mode

-- Alex

On Thu, Jun 21, 2018 at 10:57:54PM +0300, Igor Olhovskiy wrote:

> Why proxy cannot alter To header?
> 
> Regards, Igor
> 21 июня 2018 г., 19:22 +0300, Kevin Olbrich <ko at sv01.de>, писал:
> > Hi!
> >
> > I set up a proxy in front of an asterisk server to handle registration and similar.
> >
> > This setup needs topology hiding. I enabled and configured TOPOH which is working well.
> > The only header which leaks network details is "To". It lists the proxys internal IP.
> >
> > Sure, a proxy should not alter the To and I am investigating if this can be changed in asterisk but is it even possible?
> >
> > Kind regards
> > Kevin
> > _______________________________________________
> > 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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-- 
Alex Balashov | Principal | Evariste Systems LLC

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