How to force UDP packet size?

Nicola Gatti

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Jan 6, 2004, 11:07:43 AM1/6/04

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I use Videolan to redirect a live video mpeg2 stream from a source with
MTU=65535 to a pc behind a firewall which receives only UDP packets with an
MTU of no more than 1500,is there a way to tell my redirecting machine to
split automatically the UDP packets? Videolan lets you change the MTU but
only for both input and output and non separately...

Neil Horman

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Jan 6, 2004, 1:17:19 PM1/6/04

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MTU is a media layer setting. Any device whcich sits on multiple
networks should be able to automatically fragment packets which arrive
from a source with a larger MTU than the destination network segment can
support. As for packet reassembly, most devices won't bother because
you never know if another packet is going to arrive, at least not
without some stateful inspection (makes for a real queueing headache).

Sorry, fragmentation should work automatically, but reassembly you're
likely out of luck on unless you want to write some code of your own on
the Videolan box.

Neil

--
Neil Horman
Red Hat, Inc., http://people.redhat.com/nhorman
gpg keyid: 1024D / 0x92A74FA1, http://www.keyserver.net

Baho Utot

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Jan 6, 2004, 7:01:05 PM1/6/04

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Neil Horman wrote:

> Nicola Gatti wrote:
>> I use Videolan to redirect a live video mpeg2 stream from a source with
>> MTU=65535 to a pc behind a firewall which receives only UDP packets with
>> an MTU of no more than 1500,is there a way to tell my redirecting machine
>> to split automatically the UDP packets? Videolan lets you change the MTU
>> but only for both input and output and non separately...
>>
>>
> MTU is a media layer setting. Any device whcich sits on multiple
> networks should be able to automatically fragment packets which arrive
> from a source with a larger MTU than the destination network segment can
> support. As for packet reassembly, most devices won't bother because
> you never know if another packet is going to arrive, at least not
> without some stateful inspection (makes for a real queueing headache).
>
> Sorry, fragmentation should work automatically, but reassembly you're
> likely out of luck on unless you want to write some code of your own on
> the Videolan box.
>
> Neil
>

Dosen't ethernet automagically limit the MTU to 1500. I think taht it does.

Nicola Gatti

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Jan 7, 2004, 4:28:07 AM1/7/04

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What I don't understand is: BOTH my two pc's are set with and MTU of 1500
but when i get the video stream from my tv provider I have to put the option
of --mtu 65535 in videolan otherwise I only get a few corrupted data,that
means that my pc gets packets of more than 1500 even if the mtu for his
network card is 1500?
After that I made some tests and I tried to simply stream an avi from my
first pc to the firewalled second,if i put --mtu with more than 1500 the
second pc doesn't get any packet,that means that the packets are not
automatically fragmented?

"Baho Utot" <baho...@philippnies-island.org> wrote in message
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Leon.

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Jan 7, 2004, 8:02:01 AM1/7/04

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> Dosen't ethernet automagically limit the MTU to 1500. I think taht it
does.

Correct, ethernet is MTU of 1500.

Nicola Gatti

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Jan 7, 2004, 7:25:24 AM1/7/04

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I did it, I run two session of videolan like that:
vlc --mtu 65535
udp:@ipprovider:port --sout='#duplicate{dst=std{access=http,mux=ts,url=127.0
.0.1:11112}}'
vlc --mtu 1500
http:@127.0.0.1:11112 --sout='#duplicate{dst=std{access=udp,mux=ts,url=ipdestination:port}}
passing through http made him resize the packets
cheers

"Nicola Gatti" <Nicola...@cern.ch> wrote in message
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