[openib-general] ib_gid_is_link_local

[Hal Rosenstock]

On Wed, 2007-01-03 at 18:14, Jason Gunthorpe wrote:
> On Wed, Jan 03, 2007 at 05:40:36PM -0500, Hal Rosenstock wrote:
> 
> > That function could be made more precise with a routing lookup. I
> > presume an invalid link local GID would fail the lookup as opposed to
> > now where it "passes".
> 
> I think it depends how you code it.. In IP-like terms you have two
> processes going on here, a route lookup and a 'neighbour lookup' (GID
> to LID/etc conversion) for the link address.
> 
> An non-existing link local GID should pass the routing lookup, but fail the
> neighbour lookup since there is no LID.
> 
> So typically you'd do the routing lookup and end up with an on-link
> GID. Then you'd do the neighbour lookup and get a link address (IB path).

I think you are talking here about the end node and router function
rather than SM/SA, right ?

And in terms of IB path lookup, is the path just local with a
destination of the neighbor (router) or global to the end point ?

> > >  Since IBA defines the link local
> > > addresses to be fe80::xxxx/64 it must test the full /64 (like ethernet
> > > does).
> > 
> > Why ? I thought that the 54 bits (after the inital 10 bits 0xFE80) were
> > constrained to be 0. If they are not, I agree but then I'm confused
> > about the discussion of those 54 bits.
> 
> They are constrained to be 0, that is why you have to test them when
> doing the routing checks (since non-zero values will be rejected by
> the HCA).
> 
> But to test if the _scope_ of the address is link local you only look
> at the first 10 bits.

Right.

> > > Well, I'd say you have a hard wired routing table with 3 entires:
> > > 
> > > fe80::/64 onlink
> > > DEFAULT_PREFIX::/64 onlink
> > > default unreachable
> > 
> > Perhaps default is assumed "reachable" in experimental router mode.
> 
> As an initial start I'd like to see support for an entry like this:
> 
> default via fe80::17:77ff:feff:5
> 
> Where fe80::17:77ff:feff:5 is the GID of a router. A full table for a
> routing environment might look like:
>  
> fe80::/64 onlink
> fe80::/10 unreachable ; IBA requires link local scope addresses never
>                       ; to be routed
> ff00::/8 onlink       ; Multicast is 'on link'

Why is all multicast scoped onlink ? I guess this is a starting point
but not what IPoIB needs to run across IB subnets.

> DEFAULT_PREFIX::/64 onlink
> default via fe80::17:77ff:feff:5
> 
> Matching is always done by longest prefix match.

Yes.

-- Hal

> Jason