[OpenSIPS-Users] UDP fragmentation in reply routes

[Giovanni Maruzzelli]

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> 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> *För *Maxim Sobolev
> *Skickat:* den 18 maj 2020 22:03
> *Till:* OpenSIPS users mailling list <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> 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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