[openib-general] RDMA CM and loopback addresses

[Sean Hefty]

Jason Gunthorpe wrote:
> If you disable all packet filtering and you have two hosts
> [10.0.0.1 and 10.0.0.2] doing the following on .2:
> 
> ip route add 127.0.0.1 via 10.0.0.1 dev eth0
> telnet -b 10.0.0.2 127.0.0.1
> 
> And it will connect to .1's server. Turn rp_filter back on and it will
> stop working again.

Thanks - I'll give this a try and see what happens.

>>From an admin perspective it seems to me the proper thing for CMA to
> do for outgoing would be:
> - Connections with a 0 source use the destination info to consult
>   the routing table to assign the correct source address

This is the current behavior.

> - Then consult the route table with a full tuple
>   <src,dst,sport,dport,tclass,etc> to determine what device to send
>   out on

Is it necessary to access the routing table twice?  With IB, once a source 
address is obtained from the step above, it's mapped to a local IB device, and 
the connection is established from that RDMA device.

> Basically I'd expect all the advanced routing features in linux,
> including policy routing, to work properly for RMDA connections.

I agree, that would be ideal.

> For incoming I'd expect:
> - Incoming connections *optimally* would include the src socket
>   information so that that various policy mechanisms will work.

Source address information is provided, but to be clear, we're not using sockets.

> - Then the src/dst should run through the policy stuff to see if the
>   connection request should be dropped

This is not handled.  I would need to see how to enable these checks.

> - Finally a full tuple route table lookup is done to ensure that a
>   outgoing route exists with the proper outgoing device. (Even if it
>   isn't the shortest prefix or lowest metric route)

This is also not yet done.

Thanks for the feedback.

- Sean