Re: ifconfig eth0 mtu 2000: SIOCSIFMTU: Invalid argument

Ion Badulescu (
Mon, 4 Nov 1996 11:45:47 -0500 (EST)

On Mon, 4 Nov 1996, Michael L. Galbraith wrote:

> > Care to specify what kernel version you're using?
> Redface. I noticed the omission right after xmit. 2.0.24 was my victim.

The max 1500 MTU limit on Ethernet is enforced by the kernel since early
2.0.x/late pre-2.0.

> > No, a bug was fixed. 1500 is the maximum MTU for Ethernet.
> Bug? I've set the mtu > 1500 on other systems too.

The Ethernet specs allow up to 1500 bytes of data per frame. The IP layer
has to fragment large IP packets, so that's where MTU gets used. If you
set it to larger than 1500, it _might_ work, but it's not guaranteed to
work - the Ethernet layer does not do fragmentation, as it has no idea
about IP fragments, so it will pass the large packets along and pray.

But again, the newer kernels don't even let you set an MTU large than 1500
over Ethernet.


Ionut Badulescu - Columbia College '98
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