Subject: Re: NHRP question

From: [email-masked] (Rajeev Gupta)
Date: Wed, 19 Nov 1997 17:04:32 -0800

> From: Yakov Rekhter <[email-masked]>
> 
> The text I was referring to originally doesn't say anything about
> constraining the use of anycast/multicast addresses to
> registration only, but talks about NHRP Requests in general:
> 
>    If an NBMA technology offers a group, an anycast, or a multicast
>    addressing feature then the NHC may be configured with such an
>    address which would be assigned to the appropriate NHSs.  The NHC
>    might then submit NHRP Resolution Requests to such an address,
>    eliciting a response from one or more NHSs, depending on the response
>    strategy selected. 

The NHC is configured with the address(es) of the serving NHS(s)
which are located in the router(s) serving the LAG to which the
NHC belongs. The NHC establishes a connection towards the
configured address and forwards resolution requests on that 
connection.

If the address is an anycast address, then the connection will be a
point-to-point connection and resolution requests will be received by
exactly one NHS.

If the address is a multicast address (not available yet in ATM),
then the connection will be a point-to-multipoint connection
and the resolution requests will be received by all NHSs that
are the leaves of the connection. The NHC will receive multiple
responses in this case (on the same pt-mpt  or different connection,
depending on the NBMA capabilities). I think this is more a
theoretical possibility than an actual one.

Multicast addresses raise the question of which are the "appropriate
NHSs" that should be assigned to a multicast address i.e. scoping
rules. It is not clear to me if there is value in having one
NHC talk to multiple NHSs and make a path selection from the
multiple resolution responses it receives - this is better done
by the routing protocols as they can select the best NBMA target
for reaching the destination.

______________________________________________________________________
Rajeev Gupta                            Trillium Digital Systems, Inc.
mailto:[email-masked]                     http://www.trillium.com

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From: Yakov Rekhter <[email-masked]>
Date: Thu, 20 Nov 97 06:35:15 PST

Rajeev,

> point-to-point connection and resolution requests will be received by

Since according to Joel all the NHSs on an NBMA could have the same
anycast address, if the address(es) of the servicing NHS(s) 
are anycast/multicast, then what are the mechanisms by which such a
point-to-point connection will be established only to the NHS(s)
serving the LAG that the NHC belongs to.

> theoretical possibility than an actual one.

Since all the NHSs on an NBMA network could have the same
multicast address, what are the mechanisms by which such a point-to-multipoint
connection will be established only to the NHS(s) serving the
LAG that the NHC belongs to.
  
Yakov.

---

From: Joel Halpern <[email-masked]>
Date: Thu, 20 Nov 1997 13:13:41 -0500 (EST)

> serving the LAG that the NHC belongs to.
NHS have anycast and unicast addresses.  The anycast addresses are used by
the clients to find an NHS.  The unicast addresses are used in the peering
between routers (NHS).  Those paths are then used to forward the
registration towards a router(NHS) who serves the LAG.  The result is that
an initial p-to-p VC is established to an arbitrary NHS.  A correct NHS
connects back to the user, and that VC supercedes the original one.

ANYCAST is NOT multicast.  There is no ATM Multicast VC based on a single
address.  When you connect to ANYCAST, you get to ONE place.

 > > If the address is a multicast address (not available yet inATM), 
There are none because this form of multicast does not exist and is not
planned for ATM.

Yours,
Joel M. Halpern                         [email-masked]
Newbridge Networks Inc.