[OpenSIPS-Users] UDP fragmentation in reply routes

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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
>>> 
>>> _______________________________________________
>>> Users mailing list
>>> Users at lists.opensips.org
>>> http://lists.opensips.org/cgi-bin/mailman/listinfo/users
>> 
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