[crossbow-discuss] Networking problem between virtual hosts on a single machine...

James Carlson
Thu, 15 Jul 2010 20:11:55 -0000

> Well, I''m the system administrator and I did pretty much what
I''ve always done for ethernet MTU''s - use the default. This is
the first time I''ve ever seen the default set to anything other than
1500 which is why I didn''t check this. I checked and the bnx driver
having the default MTU set to 1496 is a bug (6941451) fixed in build 143 which
it doesn''t appear I''m going to see for a while. There is
nothing in the bug to indicate why it was set to 1496 instead of 1500. Hopefully
it wasn''t to avoid another problem.  I might just try upping the bnx
MTU to 1500 and see what happens. If all appears cool that might be the best fix
until build 143 comes around.

OK; that makes sense.

> By the way, you can''t use dladm to set the MTU less than 1500.
You can set it with ifconfig and possibly via the driver''s .conf file
(I''ve not tried).

For what it''s worth, setting the mtu by way of ifconfig only affects
IP.
 If you have other protocols running on that interface, you''ll need to
deal with them separately.

I''d thought that the allowable MTU values were a function of the driver
itself rather than a global restriction.  But I''ll admit that I
don''t
know enough about that lower layer.