[zeromq-dev] Limited UDP Message Size

[Stephan Opfer]

Okay, so then my suggestion would be ~2^16 bytes as maximum value, but a 
default value of 8191 bytes or lower. Plus the option to change the 
value, in order to make libzmq applicable in local network applications 
that use larger UDP messages (e.g. a team of service robots cooperating 
in your household). Further an API level error message or assert, that 
shortly explains the issue when sending UDP messages, larger than the 
value set.

Thoughts?

On 12.01.20 23:04, Greg Young wrote:
> If not clear ... if you are on a network *you control* is very 
> different than being on one you do not.
>
> On Sun, Jan 12, 2020 at 5:02 PM Greg Young <gregoryyoung1 at gmail.com 
> <mailto:gregoryyoung1 at gmail.com>> wrote:
>
>     This is correct ... Some things may not accept/forward it.
>
>     Beyond that its common for things to get *added to it* thus you
>     want to be below. Consider a case where its being wrapped
>     (tunneling is a good example).
>
>     Over the internet the maximum completely safe size is even smaller
>     around 500-600 bytes :O You can usually get above this but +- 1k
>     is about the limit.
>
>
>     On Sun, Jan 12, 2020 at 4:42 PM Stephan Opfer
>     <opfer at vs.uni-kassel.de <mailto:opfer at vs.uni-kassel.de>> wrote:
>
>         Ah okay. I read some posts about MTU and fragmentation. So in
>         theory  2^16= 65536 Bytes should be possible, but not all
>         nodes will accept such large UDP packets and support the
>         fragmentation of it?
>
>         FYI: My use case is that of a local network (IOT + Autonomous
>         Robots) and increasing the size would help me. :)
>
>         On 12.01.20 13:25, Doron Somech wrote:
>>         We can increase it to around 65,000 bytes, however, large UDP
>>         packets would probably be dropped when traveling outside your
>>         local area network.
>>         The safe size for the UDP packet to travel outside of the
>>         local area network is around 500 bytes.
>>         If you do want to use large UDP packets on your local area
>>         network you might want to increase the network MTU (jumbo
>>         frames) for better delivery.
>>
>>         For example, some AWS instances support 9001 bytes MTU for
>>         inter-instance communication.
>>
>>
>>         On Fri, Jan 10, 2020 at 3:25 PM Stephan Opfer
>>         <opfer at vs.uni-kassel.de <mailto:opfer at vs.uni-kassel.de>> wrote:
>>
>>             Hi all,
>>
>>             since 2016 there is this issue
>>             (https://github.com/zeromq/libzmq/issues/2009) about some
>>             limitations of
>>             the udp_engine in libzmq.
>>
>>             Is it possible that someone at least will increase the
>>             "#define
>>             MAX_UDP_MSG 8192" in libzmq/src/udp_engine.hpp to some
>>             reasonable value?
>>             For example "ZMQ_MAX_MSGSZ" from the zmq context option,
>>             which is MAX_INT.
>>
>>             Maybe, someone could spare some time at the Hackathon... ;-)
>>
>>             Greetings,
>>
>>                Stephan
>>
>>             -- 
>>             Distributed Systems Research Group
>>             Stephan Opfer  T. +49 561 804-6279  F. +49 561 804-6277
>>             Univ. Kassel,  FB 16,  Wilhelmshöher Allee 73, D-34121 Kassel
>>             WWW: http://www.uni-kassel.de/go/vs_stephan-opfer/
>>
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>
>         -- 
>         Distributed Systems Research Group
>         Stephan Opfer  T. +49 561 804-6279  F. +49 561 804-6277
>         Univ. Kassel,  FB 16,  Wilhelmshöher Allee 73,  D-34121 Kassel
>         WWW:http://www.uni-kassel.de/go/vs_stephan-opfer/
>
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>
>
>     -- 
>     Studying for the Turing test
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>
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-- 
Distributed Systems Research Group
Stephan Opfer  T. +49 561 804-6279  F. +49 561 804-6277
Univ. Kassel,  FB 16,  Wilhelmshöher Allee 73,  D-34121 Kassel
WWW: http://www.uni-kassel.de/go/vs_stephan-opfer/

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