Re: router-router NHRP

[Dimitry Haskin <[e-mail]>]

Yakov,

> Subject: Re: router-router NHRP 
> Date: Wed, 08 Nov 95 15:16:10 PST
> From: Yakov Rekhter <[e-mail]>
> 
> Dimitry,
> 
> > I guess I misunderstood implications of the "first NHRP target
> > constraint" of your proposal:
> > 
> >  "This document constrains an NHRP target by requiring that all the
> >   destinations covered by the target must form a subset of the NLRI of at
> >   least one route in the Forwarding Information Base (FIB) of the router
> >   that either originates, or propagates an NHRP Request. For the rest of
> >   the document we'll refer to this as the "first NHRP target
> >   constraint".  A router can originate and/or propagate an NHRP Request
> >   only if the NHRP target of the Request does not violate the first NHRP
> >   target constraint.
> > 
> >   A route (from a local FIB) whose NLRI forms a minimal superset of all
> >   the destinations covered by the NHRP target is called an "NHRP
> >   forwarding route". Observe, that by definition the set of destinations
> >   covered by an NHRP target always exhibits a subset relation to the set
> >   of destinations covered by the NHRP forwarding route associated with
> >   the target."
> > 
> > Doesn't it require a forwarder to have a route for each potential target?
> > If so, in many cases where a large scale aggregation is not possible, it coul
> d
> > be a lot of routes.
> 
> The intention of the "first NHRP target constraint" is to preserve
> the "longest match" semantics. To illustrate what was the intention
> consider an NHRP Request for the 192.9/16 target. If such a Request
> arrives at a router whose FIB contains a route to 192.9/16 and a route
> to 192.9.200/24, and both of these routes have different next hops, then
> the router should not propagate the Request, but should just send back
> a Reply (with itself as the Next Hop). 
> 
> On the other hand, if the Request arrives at a router that has
> a route to 192/8 in its FIB, and no routes more specific than this
> route, then the router should forward the Request. The router need
> not instantiate a route to 192.9/16.
> 

I don't believe you've answered my question on the *implication* (not
intention) of the "first NHRP target constraint".  To reiterate,  does
this constraint require that a Request can be only originated if
a route to the requested target is already present in the originating
forwarder FIB?  And if so, wouldn't it mandate a large FIB in some cases?

Believe me or not but I am aware of a big corporate entity that intends
to carry > 40,000 non-aggregatable routes in a routing domain.

Dimitry