[openib-general] RDMA Generic Connection Management

[Yaron Haviv]

> -----Original Message-----
> From: openib-general-bounces at openib.org [mailto:openib-general-
> bounces at openib.org] On Behalf Of James Lentini
> Sent: Monday, August 29, 2005 3:35 PM
> To: Guy German
> Cc: openib-general at openib.org
> Subject: Re: [openib-general] RDMA Generic Connection Management
> 
> 
> What happens if multiple devices can reach the destination address?
> How will they be enumerated to the consumer?
> 

Since its an IP based approach, it will work like traditional IP
A preference is given to a device with the same subnet as destination
In GbE if two NICs are on the same subnet then only one will be selected

You can also use a LAG solution that will balance connections over
multiple links, but it is done at the L2-3 layers (not exposed to the
ULP)

We should probably use the same approach and provide a single device
handle to the ULP, we may have a virtual device handle representing few
similar parallel devices (just like a LAG group has a virtual MAC), also
maybe a good idea to pass an enum with some preference (e.g. single path
or redundant or ...)

Specifically in iSER the redundancy is handled in the upper layers 
The iSCSI discovery may return multiple src & dst IP addresses and the
iSCSI multipath implementation will open multiple connections.
There are many TCP/IP protocols that do that at the upper layers (e.g.
GridFTP, ..), not sure how NFS does it.

Also note that there was a new addendum to IB Multipath record query me
& Hal proposed in IBTA that enable a client to ask "what are all the
options to get from point A to point B ?", where A & B are identified by
one of the GIDs we know about, and we can specify a flag for same
port/hca/system preferences, this can be implemented under AT if we
want.

Yaron