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

[Caitlin Bestler]

> -----Original Message-----
> From: openib-general-bounces at openib.org 
> [mailto:openib-general-bounces at openib.org] On Behalf Of Roland Dreier
> Sent: Thursday, September 29, 2005 6:50 PM
> To: Sean Hefty
> Cc: Openib
> Subject: Re: [openib-general] [RFC] IB address translation using ARP
> 
>     Sean> Can you explain how RDMA works in this case?  This is simply
>     Sean> performing IP routing, and not IB routing, correct?  Are you
>     Sean> referring to a protocol running on top of IP or IB directly?
>     Sean> Is the router establishing a second reliable connection on
>     Sean> the backend?  Does it simply translate headers as packets
>     Sean> pass through in this case?
> 
> I think the usage model is the following: you have some magic 
> device that has an IB port on one side and "something else" 
> on the other side.  Think of something like a gateway that 
> talks SDP on the IB side and TCP/IP on the other side.
> 
> You configure your IPoIB routing so that this magic device is 
> the next hop for talking to hosts on the IP network on the other side.
> 
> Now someone tries to make an SDP connection to an IP address 
> on the other side of the magic device.  Routing tables + ARP 
> give it the GID of the IB port of this magic device.  It 
> connects to the magic device and run SDP to talk to the magic 
> device, and the magic device magically splices this into a 
> TCP connection to the real destination.
> 
> Or the same idea for an NFS/RDMA <-> NFS/UDP gateway, etc.
> 

Those examples are all basically application level gateways.
As such they would have no transport or connection setup
implications. The application level gateway simply offers
a service on network X that it fulfills on network Y. But
as far as network X is concerned the gateway IS the server.

I do not believe it is possible to construct a transport
layer gateway that bridges RDMA between IB and iWARP while
appearing to be a normal RDMA endpoint on both networks.
Higher level gateways will be possible for many
applications, but I don't see how that relates to
connection establishment. That would require having
an end-to-end reliable connection, complete with flow
control semantics, that bridged the two networks by
some method other than encapsulation or tunneling.