On Fri, 16 Jun 2000, John Fraizer wrote:

If I'm not mistaken, 9000bytes is the max.

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From acenic.c (By D.Becker of course)

* To enable jumbo frames, simply specify an mtu between 1500 and 9000 * bytes to ifconfig. Jumbo frames can be enabled or disabled at any time * by running `ifconfig eth<X> mtu <MTU>' with <X> being the Ethernet * interface number and <MTU> being the MTU value.

On 16 Jun 2000 michael.dillon@gtsip.net wrote:

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On Fri, 16 June 2000, "Richard A. Steenbergen" wrote:

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In a public exchange point where you're talking to multiple networks across a shared media it makes sense to do GigE, multiple GigE, 10GigE, etc,

What is the largest MTU that you can use across a GigE fabric?

Jumbo frames are not part of the 802.3z standard. I believe the talk of a standardized length is 9000 bytes, but until then it should be understood that not every vendor will support it, or support the same number (and not every driver for every NIC will support it either). Cisco claims to support up to 10420 bytes, for example. For some of the other arguements about MTU size, take a look at: http://www.columbia.edu/acis/networks/advanced/jumbo/jumbo.html

"Jumbo frames" extends ethernet to 9000 bytes. Why 9000? First because ethernet uses a 32 bit CRC that loses its effectiveness above about 12000 bytes. And secondly, 9000 was large enough to carry an 8 KB application datagram (e.g. NFS) plus packet header overhead. Is 9000 bytes enough? It's a lot better than 1500, but for pure performance reasons there is little reason to stop there, though at 64 KB we reach the limit of an IPv4 datagram. The 32-bit CRC limit though is hard to change, so for ethernet, don't expect to see frame sizes above 9000 anytime soon.

-- Richard A Steenbergen <ras@e-gerbil.net> http://www.e-gerbil.net/humble PGP Key ID: 0x138EA177 (67 29 D7 BC E8 18 3E DA B2 46 B3 D8 14 36 FE B6)