[openib-general] RDMA connection and address translation API

[Tom Tucker]

> -----Original Message-----
> From: Roland Dreier [mailto:rolandd at cisco.com] 
> Sent: Wednesday, August 24, 2005 1:17 PM
> To: Tom Tucker
> Cc: openib-general at openib.org
> Subject: Re: [openib-general] RDMA connection and address 
> translation API
> 
>     Tom> Good point, although for iWARP it will work that way that you
>     Tom> expect.  For IB, admitedly it's more complex and would
>     Tom> require ATS. There seems to be significant reluctance around
>     Tom> ATS and I don't understand the issues. Can you provide a
>     Tom> quick synopsis?
> 
> My resistance is that ATS is just complexity without any benefit.  

IMHO the benefit is that you have a transport independent addressing
mechanism -- albeit with some limitations as you've mentioned. In this
case, the vast majority of clients enjoy the benefit without suffering
the limitations.

> ... It
> doesn't provide additional security.  It doesn't solve the
> multi-homing problem we're talking about now.  

Whenever a single GID maps to multiple IP addresses, I agree, it is a
limitation. However, I don't believe that this is strictly necessary.

> ... Once you've thrown away
> information by turning your IP address into an IB GID, there's no
> magic way ATS can recreate that information and be psychic about which
> of the multi-homed IPs you actually meant.  

I agree, so don't do that. If you want it to work properly, then you
need to map GIDS to IP addresses. 

> ... So why not just put the IP
> addressing information into the CM private data, the way that the SDP
> protocol already does?
> 
>  - R.
> 

Because it would be better to configure your network "properly". Putting
IP addresses in private data is fundamentally insecure since any user
mode client can spoof the IP address.