1 Apr
2009
1 Apr
'09
4:49 p.m.
On 04/01/2009 01:35 PM, Juha Heinanen wrote:
It is more complex that it looks, proper ending in that stage will be:
- drop 200ok
- send negative reply upstream
- ack downstream
- bye downstream
- catch 200ok for by
If simply drop te 200ok, there will be retransmission flowing around.
Cheers,
Daniel
--
Daniel-Constantin Mierla
Daniel-Constantin Mierla writes:
I meant protection so that proxy does not lose control of the call. If
proper R-R processing according to specs is avoided on purpose or not by
UA, it is hard to correct something on a proxy.
Indeed, there can be an extra check there. Not
sure how much protection
it adds here. When X calls Y, if caller is trusted (e.g., auth user,
trusted peer) then either call goes to costly resource (PSTN) that is
also trusted, to a local user or untrusted destination, case in which
you route only if does not cost you anything. If local users are not
trustable and use "custom UA", then replies can go to first Via,
skipping the rest of Via stack, ignoring negative replies after 200ok.
Unless there is symmetric nat and they are forced to use the proxy, the
safest will be a b2bua.
i don't understand, how the above relates to the security issue that i
brought up. it has nothing to do with cost, but a possibility to make
uac send in-dialog requests so that they by-pass the proxy. nasty
things documented earlier can happen if that is not prevented.
Say you get a
200OK to an INVITE with spoofed r-r, should it be
dropped?
definitely yes. there could, for example, be a flag that tells if the
check needs to be done, so that you don't waste resources needlessly if
uas is trusted.