How to send Jumbo frames ?

This is a discussion on How to send Jumbo frames ? within the Networking/Device Communication forums, part of the General Programming Boards category; Hi all, I intend to develope a small utility that can send Jumbo Frames (frames that have size larger than ...

  1. #1
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    How to send Jumbo frames ?

    Hi all,
    I intend to develope a small utility that can send Jumbo Frames (frames that have size larger than 1500 octets).
    I can send normal frame only.
    I appreciate any suggestions.
    Thanks for reading the message.

  2. #2
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    what are you talking about

  3. #3
    Registered User eth0's Avatar
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    perhaps this should be in networking
    and I'm assuming that by larger than 1500, you mean packets like Ethernet which have a larger data section ?? (MTU is 1500 for TCP)
    Last edited by eth0; 06-06-2005 at 10:44 AM.
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    Yea, GigE can handle jumbo frames, but this has nothing to do with the program, Ill explain.

    As a programmer, you simply work with the API given, normally Sockets or Winsock depending on platoform, and at that level, all you care about is Layer 3 and up (IP mainly). When you send something via sockets, the OS will determine how its sent at layer 2 (Gigabit Ethernet in this case I would say), now if your NIC and Switch supports jumboframes, as well as the destination, the OS will determin weather or not jumbo frames is usable (at least this is my understanding). Basicly its not up to you, but up to the OS and its implementation of IP and the Ethernet standard. Plus, if the packet is going outside of the LAN, it should default to the normal MTU size (1500).

    Basicly, don't worry about trying to use Jumbo frames, the OS will take care of that.
    If any part of my post is incorrect, please correct me.

    This post is not guarantied to be correct, and is not to be taken as a matter of fact, but of opinion or a guess, unless otherwise noted.

  5. #5
    Registered User eth0's Avatar
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    Whatever technique you use, your jumbo frames will be fragmented anyway when they hit the WAN, as ATM can't handle anything over 53 bytes, and cuts them down.

    (note, when I said "MTU is 1500 for TCP", I meant ethernet)
    Open source isn't a matter of life or death......
    .......its much more important than that!!


    SuSE Linux - GCC 3.4.2
    XP Pro - Visual Studio 2005 TS, MinGW 3.4.2

  6. #6
    * Death to Visual Basic * Devil Panther's Avatar
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    eth, what about MPLS? how much can it handle?
    "I don't suffer from insanity but enjoy every minute of it" - Edgar Allen Poe

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  7. #7
    Registered User crepincdotcom's Avatar
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    The network stack takes care of frame size for you. If you allow jumbo frames, as root type:

    ifconfig eth0 mtu 9000

    Remember that only other computers with jumbos enable can receve what you send.

    -Jack Carrozzo
    http://www.crepinc.com/

  8. #8
    * Death to Visual Basic * Devil Panther's Avatar
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    Quote Originally Posted by crepincdotcom
    The network stack takes care of frame size for you. If you allow jumbo frames, as root type:

    ifconfig eth0 mtu 9000

    Remember that only other computers with jumbos enable can receve what you send.

    -Jack Carrozzo
    http://www.crepinc.com/

    I think you're forgetting something very simple, like the network itself!
    The fact that you can set your system's mtu path means nothing,
    that's why it's usually recommended to either use the default ethernet setting, or allow the mtu value to be set by the dhcp.

    In shot, unless you connect the two computers with a crossover cable you get nothing by setting the mtu size to 9000, since the network devices are most likely ethernet based.
    "I don't suffer from insanity but enjoy every minute of it" - Edgar Allen Poe

    http://www.Bloodware.net - Developing free software for the community.

  9. #9
    Registered User crepincdotcom's Avatar
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    But a managed switch can be changed to allow a larger MTU.
    -Jack C
    jack {at} crepinc.com
    http://www.crepinc.com

  10. #10
    * Death to Visual Basic * Devil Panther's Avatar
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    Well yes, of course! But why should you?!
    Also, it will get fragmented once it gets out of your adminitrative network, it's not like you have a closed huge network like the CIA or something

    Plus I don't think that thaipham is a network administrator.
    "I don't suffer from insanity but enjoy every minute of it" - Edgar Allen Poe

    http://www.Bloodware.net - Developing free software for the community.

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