Dealing with bogus interface-mtu responses

[David W. Hankins]

On Wed, Oct 18, 2006 at 01:41:05AM +1000, Andrew Pollock wrote:
> A while ago I was asked to make Debian's dhclient request interface-mtu, and
> I complied. It seems, however, that there are whacky devices out there that
> like to advertise stupid MTU values (like 64). See
> https://launchpad.net/distros/ubuntu/+source/dhcp3/+bug/61989 for some of
> ths discussion.

Wow.  How did they arrive at '64' I wonder?

> Ubuntu has already reverted this change, and I'm inclined to as well, for
> the sake of consistency if nothing else.
> 
> Is it feasible to have dhclient ignore a MTU size that would render it
> inoperable?

I think the most obvious thing to do is to edit the dhclient-script
where this value is passed to ifconfig, and script in a simple band
pass.

Where the $new_interface_mtu is greater than 575 and less than x, where
x is either the interface's physical limitation (eg 1501 for 10/100
ethernet), or 65536.

It depends on if 'ifconfig eth0 mtu 8192' will error or produce some
sort of broken result for which ceilling you want to apply.

-- 
David W. Hankins	"If you don't do it right the first time,
Software Engineer		you'll just have to do it again."
Internet Systems Consortium, Inc.	-- Jack T. Hankins