Re: Why is MTU an issue? (RE: Please read - proposed W G termination)

Dror Goldenberg wrote:

>
>
> > From: Mark Townsley [mailto:[email protected]]
> > Sent: Friday, September 02, 2005 10:43 PM
>
> > Dror Goldenberg wrote:
> >
> > >
> > >
> > > > From: Mark Townsley [mailto:[email protected]]
> > > > Sent: Friday, September 02, 2005 4:21 PM
> > > >
> > > > Harald Tveit Alvestrand wrote:
> > > >
> >
> > > I think that the right approach is to have a per-neighbor
> > MTU in the
> > > L2 interface. And furthermore, MTU can be different between
> > multicast
> > > and unicast. We're actually trying to see whether a per
> > neighbor MTU
> > > can be added to Linux.
> > >
> > On the face of it, "per-neighbor" MTU sounds like a
> > management nightmare
> > for anything but a handful of hosts.
> >
>
> You just need to configure for each one of your hosts an MTU for 
> ipoib-cm, or use the default one. When a connection is made, ipoib-cm 
> chooses MTU=min(local MTU, remote MTU) and you're done.
>
> Maybe you can elaborate more on why you think it's a nightmare ?
>
I probably (well, definitely) do not know enough about IB to be making 
such grand statements. But it seemed to me that if each host may have a 
different MTU, then all hosts which can talk to one another within a 
given subnet would have to know the MTU of every other host. So, a 
classic N^2 problem. Is IB natively point 2 point? Perhaps that would 
ease my fears.

- Mark