[ewg] Re: [ofa-general] [PATCH 2/9] ib_core: kernel API for GID -->MAC translations

[Jason Gunthorpe]

On Wed, Jun 17, 2009 at 11:41:28AM +0300, Liran Liss wrote:
> 
> > Why not just use IP to MAC calls?  Or use the MAC as the GUID?
> 
> We do use standard OS services to map the IP addresses (that were
> encoded in the GID) to MACs.  GIDs encode IP addresses rather than
> MACs to enable users to use the node names that they are used to.
> Specifically, we will feed in all IP addresses that were assigned to
> the Ethernet interface to the corresponding port GID table.  This
> will also enable routing in the future.

Hum, This is a very tricky subject. Co-mingling the IB GID address
space and the IPv6 address space like this is not really something
that was envisioned from the IBA side.

Also, the use of IPv4 mapped addresses presents some interesting
problems from an IB router perspective.

> The only exception is IPv6 link-local addresses, which already
> encodes the MAC.  In this case, a simple algorithmic operation
> extracts the MAC without requiring ARP, etc.

You shouldn't do this, the IPv6 link local addresses may use the MAC,
or maybe not. There are several additional IPv6 protocols like privacy
extensions and SEND that break this assumption. You still must do the
lookup if you are using IPv6 addresses.

Jason