Re: [linux-rdma and rdma-core]: Unable to perform rdma_connect in loopbacked configuration

[Jason Gunthorpe <jgunthorpe-ePGOBjL8dl3ta4EC/59zMFaTQe2KTcn/@public.gmane.org>]

On Tue, Sep 19, 2017 at 01:11:49AM +0000, Stephen  Bates wrote:
> >> Using a NAT approach discussed in [1] I can setup IPv4 addresses on
> >> both HCAs such that I avoid a local loopback (the addresses I use
> >> are a little different to the ones in that reference but the
> >> approach is identical). This allows ping, iperf and other IP based
> >> applications to work just fine. For example:
> 
> Thanks for the reply Jason
> 
> > The RDMA stuff ignores everything in iptables.
> 
> Can I ask why this is?

roce is an incomplete emulation of the netstack with hardware
offload. everything iptables is part of the incompleteness..

> > IMHO, it is also a bug if loopback roce doesn't just work out of the
> > box, fully internally to the NIC. :\
> 
> OK. Note what I am trying to get working is a bit different. It'ss
> not internal to one NIC but across two NICs in the same
> server. Loopback inside one NIC works fine.

I got that, but it makes no difference to my statement. Out of the box
the kernel should select one of the two NICs and do internal loopback.

That is consistent with the netstack semantic that the IP address is a
property of the host not the netdev.

Jason
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