Subject: Re: (ION) nhrp: Client proto addr?

From: "Paul Henri" <[email-masked]>
Date: 26 May 1998 19:29 EDT

In message "Re: (ION) nhrp: Client proto addr?", 
[email-masked]' writes:

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>> 
>> In message "Re: (ION) nhrp: Client proto addr?", you write:
>> 
>> >> Given that a non-zero prefix length in a CIE as part of a resolution
>> >> reply represents the equivalence class of IP addresses which match the
>> >> first "Prefix Length" bit positions of the destination IP address (in
>> >> mandatory part), why is it that a client IP address is necessary in
>> >> this resolution reply? Wouldn't that be redundant information?
>> >> 
>> >When a NHRP requested destination station is not on the ATM network, 
>> >the egress router to that destination serves as the Next-Hop to 
>> >that station. That is, IP address in CIE belongs to the egress router, 
>> >while IP address in mandatory part belongs to the destination.
>> >The two IP addresses are on a different network and both infos 
>> >are necessary.
>> >
>> 
>> Is the client proto address the responder, or the nhs which is
>> authoritatively serving the destination? What if the destination is an
>> atm-attached nhc; What is the client proto address in this case?
>> 
>> How does this tie in with the responder extension?
>
>Protocol Address in CIE belongs to NHC. the responder is the NHS serving
>the destination NHCs. NHC never respond to any requests. 
>
>If the destination is an atm-NHC, this would be the general case.
>The client Protocol address is the IP address assigned to the
>atm interface of the NHC.
>
>Responder extension is filled with the NHS's information.

If I understand correctly, 1) Client proto address in cie is nhc's ip
address if destination is nhc, otherwise 2) Client proto address is
egress nhs's address if destination is off the atm network.

If this is true, I have the following questions:

- What is the client proto address if an nhs responds
non-authoritatively (i.e. it is not the egress router and does not
have the nhc directly attached)?

- Of what use is the client proto address except in purge requests?
It would seem the requestor may just require a mapping between
destination ip address and atm next-hop. I don't see why the source
would care if the atm next-hop is that of a router or nhc.

Thanks,
pdh
---
Paul Henri
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From: Albert Manfredi <[email-masked]>
Date: Wed, 27 May 1998 12:57:52 -0400

> would care if the atm next-hop is that of a router or nhc.

Paul,

Perhaps it would help (me, anyway) if you specified source and
destination when you talk about protocol addresses.

The long and the short of it is that the protocol addresses, source
and destination, are the two end points of the session. The NBMA
addresses are the NBMA addresses belonging to the ingress and egress
points of whatever NBMA cloud you are in, assuming that each edge
router and the source and destination stations are all NHRP clients.

In principle, the NMBA address could also be the NBMA address of the
source and the destination stations, but that would only occur if
both were within the same NBMA cloud and if optimal IP routing
remained within that NBMA cloud from start to finish.

The reason you need the correct protocol addresses is that they are
what determines the overall route from source to destination. There
could be several NBMA clouds between this source and destination,
however. In fact, there might just be _one_ NBMA cloud, but shaped
strangely, and the proper route from source to destination might
just jump in and out of that single NBMA cloud.

I'm thinking of a snake-like ATM cloud, where IP routing determines
that the best route is not curving along the ATM cloud, but jumping
between the turns, if you see what I mean.

I hope this helps.

Bert
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