[vortex] Re: [eepro100] MTU more then 1500

[Donald Becker]

On Tue, 3 Dec 2002, Anton Yurchenko wrote:

> To: vortex@scyld.com
> Subject: [eepro100] MTU more then 1500

Did you mean to ask this question on the eepro100 list, the vortex
list, or both?

> is there a way to increase MTU to more then 1500? is it a harware or 
> driver issue?

Bogdan has answered the question for the 3c905B and 905C.
The current 3Com chips have excellent support for large MTUs.

Earlier 3Com chips (3c595, 3c905 without a suffix) support only two
sizes: 1500 bytes (standard Ethernet) and about 4400 bytes (FDDI-sized),
but few of these 5+ year old boards are still around.

The eepro100 does not support arbitrary packet sizes.

There are eepro100 patches that claim to do this, typically with the
idea of adding sleazy VLAN support.  All that these patches do is to
remove the Rx length limit.  This is trivial -- a single bit change in
the configuration table.  But by doing this you end up with a machine
that seems to work fine during all normal tests, but is not robust
against network errors or malformed packets.  Alas, I'm powerless to
prevent such subtly stupid changes from being put into the kernel --
"they are actively working on it, and your driver release doesn't have
the 'feature'".

-- 
Donald Becker				becker@scyld.com
Scyld Computing Corporation		http://www.scyld.com
410 Severn Ave. Suite 210		Scyld Beowulf cluster system
Annapolis MD 21403			410-990-9993