[openib-general] Re: port_num

[Caitlin Bestler]

Roland Dreier wrote:
>     Roland> If one offload device can share an address with the host
>     Roland> stack, why can't I give the same address to another    
> Roland> offload device? 
> 
>     Caitlin> How would you select which offload device to use?
> 
> Routing I guess.  With existing stacks, how do you select
> which non-offload device to use when multiple interfaces have
> the same IP?
> 
>  - R.

My general assumption is that the IP address is assigned to
a single offload device (or at least a set of offload devices
that are managed as a single device), and that the only sharing
is that the device can be configured to pass some IP datagrams
through for host-based processing, and only pre-empts those
directly related to established connections, requested connections
or offloaded listens.

When the host stack uses the IP address, it is using the same
offload device in its L2 mode (raw Ethernet or IPoIB). So the
routing is consistent, a given IP address is associated with
a given ingress/egress device. The only question is whether
the device's offload stack will handle the packet or the
host will.

The only real difference is that with IPoIB it is much easier
to determine which packets get passed to the host for handling.
With iWARP, context data substitutes for an on-wire wrapper.