[OpenSIPS-Users] UDP fragmentation in reply routes

Wed May 20 17:11:18 EST 2020

Hi the issue on my side is that it’s not the network that is the problem the second fragment is not even sent. I also kind on lean to TCP at the moment but it would be good to get a comment from Opensips team on this if and how they setup the sockets and if there is a difference on different routes 

Br Olle

Skickat från min iPhone

> 20 maj 2020 kl. 17:14 skrev junkmail <junkmail at djrance.com>:
> 
> Hello, I had run into the same issue.  One thing I was a bit mistaken because I was using tcpdump and doing a capture filter of port 5060 or the such.  So I was missing the Fragment in my sniff as it does not include the UDP header.  Just something to be aware of.  But I was having problems specifically traffic inside of GCP < google cloud.  As well as traffic traversing the VPN to GCP.   I am not certain about what changed for internal to GCP but that started working and now the only thing using TCP is over VPNs.   Sorry not a lot of information here. but my best guess is either the firewall/router on my side or Googles is dropping the UDP fragment.  I didn't dig into it much further as TCP fixed the issue and this was just a transit between opensisps systems.
> 
> 
> 19.05.2020 01:21 に olle at zaark.com さんは書きました:
>> 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> 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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