Thread: How to send Jumbo frames ?

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)

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.

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)

eth, what about MPLS? how much can it handle?

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.

But a managed switch can be changed to allow a larger MTU.

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.