How to force UDP packet size?

Discussion in 'Linux Networking' started by Nicola Gatti, Jan 6, 2004.

  1. Nicola Gatti

    Nicola Gatti Guest

    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...
     
    Nicola Gatti, Jan 6, 2004
    #1
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  2. Nicola Gatti

    Neil Horman Guest

    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, Jan 6, 2004
    #2
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  3. Nicola Gatti

    Baho Utot Guest


    Dosen't ethernet automagically limit the MTU to 1500. I think taht it does.
     
    Baho Utot, Jan 7, 2004
    #3
  4. Nicola Gatti

    Nicola Gatti Guest

    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?

    does.
     
    Nicola Gatti, Jan 7, 2004
    #4
  5. Nicola Gatti

    Nicola Gatti Guest

    I did it, I run two session of videolan like that:
    vlc --mtu 65535
    udp:mad:ipprovider:port --sout='#duplicate{dst=std{access=http,mux=ts,url=127.0
    ..0.1:11112}}'
    vlc --mtu 1500
    http:mad: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, Jan 7, 2004
    #5
  6. Nicola Gatti

    Leon. Guest

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

    Correct, ethernet is MTU of 1500.
     
    Leon., Jan 7, 2004
    #6
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