[OpenSIPS-Users] UDP fragmentation in reply routes

Tue May 19 07:21:01 EST 2020

Hi, this happens one single opensips instance server it receives the inbound packet fine, then when its send out on the same interface it’s fragmented, so I don’t think it’s network or router switch related. Have seen such problems in the past in virtual environments but this is not the case now.

My prime suspect is Centos since it send out the first part of the fragmented packet but not the following part that would complete the packet.

But indeed it is a strange bug, since it does not always happen.

BR/Olle

Från: Users <users-bounces at lists.opensips.org> För Giovanni Maruzzelli
Skickat: den 19 maj 2020 09:13
Till: OpenSIPS users mailling list <users at lists.opensips.org>
Ämne: Re: [OpenSIPS-Users] UDP fragmentation in reply routes

Can be a problem of the virtual env, and/or the router/switch...

Try substitute real hardware to virtual, and different models of router/switch

In a LAN, UDP fragmentation is not supposed to be a problem at all...

answered from mobile, please pardon terseness and typos,
-giovanni

On Tue, May 19, 2020, 08:05 <olle at zaark.com <mailto:olle at zaark.com> > wrote:

Thanks for the reply Max, 

we are doing all we can to make the packets smaller, but before we move over to TCP, which is most likely our next step, I wanted to explore what could be happening.

AFAIK the application have some control of this since these are parameters that partly can be set when you open a socket, that’s why I wonders if Opensips might use those parameters or not, especially since we have so very different behaviour in different directions.

BR/Olle

Från: Users <users-bounces at lists.opensips.org <mailto:users-bounces at lists.opensips.org> > För Maxim Sobolev
Skickat: den 18 maj 2020 22:03
Till: OpenSIPS users mailling list <Users at lists.opensips.org <mailto:Users at lists.opensips.org> >
Ämne: Re: [OpenSIPS-Users] UDP fragmentation in reply routes

Smells like a OS/kernel bug to me. There is little application can do in that regard, UDP fragmentation/reassembly happens at much lower layers of the OSI stack.

However, as a workaround as long as SIP goes you can try to reduce your SIP signalling packet size by using compact version of SIP headers, as well as dropping headers that are not used. That would save you 100-150 bytes per SIP message perhaps. I don't know if OpenSIP can do that in the proxy mode out of the box though, so you might want to add b2b into the flow.

-Max

On Mon., May 18, 2020, 12:34 p.m. Olle Frimanson, <olle at zaark.com <mailto:olle at zaark.com> > wrote:

Hi,

We have an issue on our home proxy (opensips 2.4.6), when it receives  200 OK (over UDP)  from our Freeswitch and the package size is higher than the MTU size , we sometimes get fragmentation  of the UDP packets, but only the first part of the fragmented package is sent to our edge proxy. Is this a known issue or is it a OS bug?

We have not yet spotted any pattern on this and in most cases bigger packets with MTU around 1600 bytes gets through without an issue.

I can add that in the other direction in the normal request routes we don’t have any issue at all can have packets > 2000 bytes without any issues.

Does Opensips use IP_MTU_DISCOVER or how is fragmentation controlled and is it expected to have different behavior in reply routes vs other routes?

We use Centos 7 in a virtual server environment.

I was hoping someone can share some light on this strange issue.

BR/Olle

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