[SR-Users] SIP messages over UDP with sizes over MTU

Yufei Tao yufei.tao at gmail.com
Wed Apr 1 15:42:09 CEST 2015


We've got Kamailio (v4.0.0) connected to some SBC, which sends SIP traffic
and periodic OPTIONS pings to Kamailio's VIP. Kamailio responds to the
OPTIONS pings with OK, i.e. in the  main route block:
   if (is_method("OPTIONS"))

All works fine for a week or so, then Kamailio stopped responding to the
OPTIONS pings on the VIP it listens to. But it still respond to OPTIONS
pings that are sent to its real IP. The real IP is not used for
receiving/sending any traffic while only the VIP is. So it seems that
Kamailio is still working, but maybe having problems with the receiving
buffer for the VIP?

We do see that some SIP messages sent to Kamailio's VIP are too big
(sometimes over 1500 bytes). My question is, in this case, what would be
expected to happen? Is it possible somehow the receiving buffer for the VIP
got messed up by the big UDP messages? Any one seen similar problems? What
is the suggested solution?

We're considering moving to TCP. But since this is production environment,
I want to get some confidence that the problem we saw was likely to have
been caused by the UDP message being too large.

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