[OpenSIPS-Users] UDP fragmentation in reply routes

Wed May 20 19:56:21 EST 2020

Hi thanks for the tip, how dit you find it? I just capture 3 ports in my tcpdump.

Br Olle

Skickat från min iPhone

> 20 maj 2020 kl. 19:18 skrev junkmail <junkmail at djrance.com>:
> 
> Sorry that is what I was trying to let you know.  Is that I had thought the same thing that the Fragment was not even sent, but it was just because of the tcpdump filter I had not that it actually wasn't being sent.  If you have not try capturing all IP traffic to a host IP and see if you see it.
> 
> 
> 20.05.2020 11:11 に Olle Frimanson さんは書きました:
>> 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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