Date: Fri, 1 Jun 2012 16:19:47 +0000 From: "Pieper, Jeffrey E" <jeffrey.e.pieper@intel.com> To: John-Mark Gurney <jmg@funkthat.com>, "Bjoern A. Zeeb" <bzeeb-lists@lists.zabbadoz.net> Cc: "freebsd-net@freebsd.org" <freebsd-net@freebsd.org> Subject: RE: if_em and large mtu bug? Message-ID: <2A35EA60C3C77D438915767F458D6568481AA470@ORSMSX101.amr.corp.intel.com> In-Reply-To: <20120601065219.GF91292@funkthat.com> References: <4FC5FA0B.5010609@cran.org.uk> <4FC6062A.3010002@rdtc.ru> <BEEA95C1-FFC4-467A-ACC9-64A420EE8D7A@lists.zabbadoz.net> <20120601065219.GF91292@funkthat.com>
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-----Original Message-----
From: owner-freebsd-net@freebsd.org [mailto:owner-freebsd-net@freebsd.org] On Behalf Of John-Mark Gurney
Sent: Thursday, May 31, 2012 11:52 PM
To: Bjoern A. Zeeb
Cc: freebsd-net@freebsd.org
Subject: Re: if_em and large mtu bug?
Bjoern A. Zeeb wrote this message on Wed, May 30, 2012 at 22:26 +0000:
> On 30. May 2012, at 11:36 , Eugene Grosbein wrote:
>
> > 30.05.2012 17:44, Bruce Cran ??????????:
> >> Are there any known problems with if_em and jumbo packets? I've found
> >> that my ssh connection breaks (when running dmesg etc.) if I configure
> >> the mtu to 9216 via rc.conf - but if I initially use a 1500 byte mtu and
> >> then manually configure it to 9216 then no problems occur.
> >>
>
> That is due to another known bug;
> if you check netstat -rn and the mtu there on your routes you'll figure.
> if you remove your addresses/routes and re-add them after changing the mtu,
> you'll see it as well.
Just to comment, this isn't a bug.. it's that FreeBSD allows you to
control the mtu to a host via the routing table... Previously it would
always max out the routes MTU meaning that you could never reduce the
MTU to a problematic host, while keeping the mtu larger for others i.e.
have a mixed network w/ jumbo and normal frames...
--
John-Mark Gurney Voice: +1 415 225 5579
"All that I will do, has been done, All that I have, has not."
This is what I use (I'm JFV's validation engineer):
Ifconfig emX <hostname> mtu <mtusize>
Doing this adds it to the routing table and seems to avoid any issues.
I hope this helps,
Jeff
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