[ofa-general] RE: IPoIB CM connectivity issue.

[Alex Estrin]

> 
>  > In second case (when OFED is CREQ initiator) only one RC 
> QP was used
>  > to establish a connection and apparently bidirectional traffic was
>  > capable to go through that one QP.
> 
> Yes, at least in the case where you have an SRQ-capable adapter, it
> doesn't really matter which QP has incoming traffic.  However, it was
> much simpler in the IPoIB implementation to simply open a QP to send
> traffic rather than searching through all passive connections for a
> connection to the same peer.
> 
> Is this behavior causing problems for you?

I just didn't expect of using TWO QPs per one connection.
It probably won't simplify my implementation :)

>  > > I assume you mean sending ARP replies.  Yes, you are 
> correct.  I never
>  > > noticed before but RFC 4755 does say:
> 
>  > >    Additionally, all address resolution responses (ARP 
> or Neighbor
>  > >    Discovery) MUST always be encapsulated in a UD mode packet.
> 
>  > Yes, you are right. Please discard my note regarding ARP reply.
> 
> Not sure what you mean -- if Linux is sending ARP replies on 
> a connected
> QP, then that is not allowed according to the RFC.

I meant "Linux sends ARP reply over UD" behaviour is in compliance with
the document.

> However, looking at this quote again I see that the RFC's requirement
> rather unfortunately includes neighbour discovery too.  It's not *too*
> bad to look at the ethertype in the IPoIB pseudo-header to 
> check for an
> ARP packet, but sending all neighbour discovery messages 
> seems very ugly
> -- even just sending all ICMP6 messages via UD wouldn't be 
> very nice to
> implement, and it would eg break ping6 with large messages, 
> so we would
> have to look deep deep into packets to see which were ND messages.
> 
> I wonder what the rationale behind that part of the RFC was?
> 
>  - R.
Yes, it would be good to know the reason behind this. So far handling ND
messages over UD ONLY 
seem odd considering it's function to detect unreacheable neighbours.
If one has alive RC QP to a neighbour most likely it is reacheable.

Alex.