[OpenSIPS-Users] UDP fragmentation in reply routes
Olle Frimanson
olle at zaark.com
Thu May 21 05:52:25 EST 2020
Thanks for the tips will give it a try to see what happens, but I guess TCP is the solution.
Br Olle
Skickat från min iPhone
> 21 maj 2020 kl. 07:41 skrev junkmail <junkmail at djrance.com>:
>
> Yea that is it.
>
> so if you are doing something like tcpdump udp port 5060 or udp port 5080 etc. you would have to change it to the specific host IP that you are testing with.
>
> so more like tcpdump host 10.1.1.1 or something like that to make sure that you see all the traffic. Or I am sure there is a way to tell TCPdump to capture fragments but I am a bit too lazy to look it up. But that was why I was not seeing the fragments.
>
>
>
> 20.05.2020 15:46 に Maxim Sobolev さんは書きました:
>> Olle, this is what he has been warning you about. See, the
>> fragmentation is done at IP level, so that if your UDP packet gets
>> fragmented, only the first fragment is going to contain a UDP header
>> with a port number. Therefore, if you are using a port number(s) as a
>> capture filter with your tcpdump then you won't see those subsequent
>> fragment(s). You should be using IP with destination address as a
>> filter for example and not UDP with a port number(s). Or combine udp
>> rule with rule that would only match IP fragment(s).
>> -Max
>>> On Wed, May 20, 2020 at 12:57 PM Olle Frimanson <olle at zaark.com>
>>> wrote:
>>> 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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