[openib-general] [RFC] IB address translation using ARP

[Michael Krause]

At 07:45 AM 10/10/2005, Hal Rosenstock wrote:
>On Sun, 2005-10-09 at 10:19, Sean Hefty wrote:
> > >I think iWARP can be on top of TCP or SCTP. But why wouldn't it care ?
> >
> > I'm referring to the case that iWarp is running over TCP.  I know that 
> it can
> > run over SCTP, but I'm not familiar with the details of that 
> protocol.  With
> > TCP, this is an end-to-end connection, so layering iWarp over it, only the
> > endpoints need to deal with it.  I believe the same is true for SCTP.
>
>Yes, SCTP is similar in those regards.

SCTP creates a connection and then multiplexes a set of sessions over 
it.  You can conceptually think of it as akin to IB RD but where all QP are 
bound to the same EEC.


> > >Doesn't a routing decision still need to be made at the IP layer ?
> >
> > Routing of the IP packets is done at the IP layer, but I don't see how this
> > affects iWarp.
>
>It does under the "covers", those covers being IP routing.

iWARP uses IP routing so there is zero difference between iWARP and any 
other IP-based protocol suite that operates above the IP layer.


> > >Doesn't the IP next hop need to be determined (e.g. gateway when the
> > >destination is off the local IP subnet) ? Is there something that
> > >precludes iWARP from working across IP subnets ?
> >
> > I can't think of anything that would preclude iWarp from working
> > across subnets.
>
>Doesn't the IP next hop need determining in that case ? Why is that not
>relevant ? I don't think the iWARP connection is end to end in all
>cases.

TCP / SCTP are end-to-end thus iWARP is end-to-end.  The fact that there is 
an intermediate router / gateway between does not matter.  That is just a 
bit of IP routing to forward the packets.  The ARP / ND protocols determine 
the next hop for the IP layer thus iWARP just like TCP/SCTP is not affected 
or cognizant of the underlying fabric topology.

Mike 
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