Re: oversize frame

[David Young <dyoung%pobox.com@localhost>]

On Wed, Mar 26, 2014 at 10:35:43PM -0700, Aaron J. Grier wrote:
> (necromancing old threads...)
> 
> On Fri, Nov 08, 2013 at 11:09:59AM -0500, Michael T. Davis wrote:
> >     Every so often, the NetBSD-6 kernel reports...
> > 
> > Nov  8 09:44:17 fw /netbsd: wm1: discarding oversize frame (len=1518)
> > 
> > It only ever cites wm1 and the length is always 1518.  Since the MTU
> > for this interface is set to 1500, doesn't this mean that another
> > system attached to that interface is generating an invalid packet,
> > presumably due to a mis-configuration?
> 
> FWIW I see this on nfe on my sunfire x2200m2.  the nfe is attached by a
> vlan, but vlan packets are 1504 bytes -- 1518 seems a very strange
> number.

I recognize the number, here is how I think it comes about: 6-byte
destination MAC + 6-byte source MAC + 2-byte outer ethertype (VLAN) +
2-byte VLAN tag + 2-byte inner ethertype + 1500 MTU = 1518 bytes.

Dave

-- 
David Young
dyoung%pobox.com@localhost    Urbana, IL    (217) 721-9981