[Freeswitch-users] SIP Invite IP fragmentation issue

Ken Rice krice at suspicious.org
Tue Nov 18 02:29:28 PST 2008

Its not really possible other then enabling compact headers or by getting
rid of codecs that you don¹t actually want to use... Another thing you could
do is get your broken ISP to fix their firewall... It is not correct to just
drop fragmented packets just because they are fragmented.. This is something
that will happen on a regular basis on the internet as not everything has an
MTU of 1500

From: Saurabh Aggarwal <saurabh_aggarwal at hotmail.com>
Reply-To: <freeswitch-users at lists.freeswitch.org>
Date: Tue, 18 Nov 2008 10:19:55 +0000
To: <freeswitch-users at lists.freeswitch.org>
Subject: Re: [Freeswitch-users] SIP Invite IP fragmentation issue

Ok, my bad. Ethereal for some reason was showing only the first fragment
(ethereal bug?).
But, now it seems I have hit another problem - it seems that the SIP invites
(which are fragmented) are being dropped by the firewall in between us and
the SIP provider. Is it possible to shrink the size of the SIP invite so
that it fits in a single packet? Any optional stuff in the SIP invite that
is sent, that can be thrown away?

From: saurabh_aggarwal at hotmail.com
To: freeswitch-users at lists.freeswitch.org
Date: Tue, 18 Nov 2008 07:34:11 +0000
Subject: [Freeswitch-users] SIP Invite IP fragmentation issue

I am having an *odd* issue, which i am not sure freeswitch is to be blamed
Sometimes, the SIP invites are bigger than 1500 bytes causing IP
fragmentation, but when I look at the TCP dump (on the same machine as
freeswitch), I see that only the first packet of the fragment is captured.
Is freeswitch trying to do its own IP fragmentation or is it relying on
underlying linux (kernel 2.6.18)?
I created a small program to send UDP packets of 2000 bytes, and also tried
with ping -s 2000, and both were successful, so am leaning towards blaming
Any suggestions?

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