Subject: Re: (ION) RFC 2332 again

From: "Albert Manfredi" <[email-masked]>
Date: Wed, 11 Nov 1998 16:46:15 -0500

-----Original Message-----
From: Archana Nehru <[email-masked]>
Date: Wednesday, November 11, 1998 3:59 PM
Subject: Re: (ION) RFC 2332 again

>Albert Manfredi wrote:
>> I guess I'm missing something you're saying here, Archana.
>>
>> Let's say the NHC registers with its NHS. All the NHC
>> can possibly say to the NHS is "I am ATM address ____
>> and IP address ____ and IP mask ____." That's it. The
>> NHC has no idea what sort of IP routing that NHS is
>> doing. That NHC's NHS might be the edge router for
>> _only_ the NHC's IP subnet, or it might be the edge router
>> for a whole bunch of other subnets as well. How is the
>> NHC to know?
>
>The NHC does not know what all the NHS is routing,
>but it definitely should know the topology to the extent that it
>knows why it registered an entire subnet with the NHS. This
>will happen only when the NHC is the only route to the
>"registered subnet" and NHC knows that it wont cause
>any routing loops etc by registering this information.

Perhaps we are having a semantics problem. The NHC you are
postulating here, the one registering a route to a whole subnet, is
this not the NHC module of a router, i.e. the NHC module of a box
that is also an NHS? If the answer is yes, then are you not simply
describing the case where a new NHS comes on line, and the other NHS
must then react to the new routing options just come available?

>NHC cannot
>register a subnet that it has learnt through routing,
>because such destinations typically are not stable.
>Since an NHS can generate resolution requests
>only for registered destinations, all it has to do is
>look up if it serves the destination in its registered
>cache and if some NHC has registered it, then the
>prefix length could directly be the registered one
>itself. If the destination is not found served by any
>registered NHC, NHS has to forward it etc.

Seems to me you are describing a new NHS entering into the network.

>>For all the NHC knows, that NHS might be
>>responding to 1.x.x.x/8.
>
>I am not sure what you mean here. The basic
>assumption is that an NHS cannot reply unless it
>finds a registered NHC claiming that it represents
>the 1.x.x.x/8. If there is , then NHS has to reply
>back. If not, forward it.

I was describing the simple case of an NHC that is _not_ an IP
router registering with its NHS (typically, its default IP router).
In this case, the NHC is merely an IP over ATM host, member of some
IP subnet, that wants to let its NHS know how other ATM hosts in the
ATM cloud can find a shortcut to it.

Assume that this NHS is the router for several different IP subnets
within this same ATM cloud. A reasonable assumption, but the newly
registered NHC would have no clue.

Bert
[email-masked]

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---

From: Archana Nehru <[email-masked]>
Date: Wed, 11 Nov 1998 14:20:07 -0800

> must then react to the new routing options just come available?

No I was only referring to an NHC on a router without any NHS. 
     NHS------NHC-----SUBNET
here NHS and NHC are both routers and have only NHS and NHC
functionality respectively.If the NHC was an NHS-NHC , then probably
there was no need for NHC to register the subnet with  the NHS, since
the NHS-NHC combination could as well reply to the resolution request.

> registered NHC would have no clue.

True, just like a CIP client in a LIS..in such a case the NHC wont have
registered any prefix with the NHS. And there is probably no use in
determining the prefix length here because, the NHC ATM address is not
valid for any range of addresses but itself..isnot it?

-archana
-- 

________________________________________________________________________
Archana Nehru                     :  Trillium Digital Systems, Inc 
E-mail: [email-masked]       :  Los Angeles, California     
Phone: +1 310 442 9222     
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---

From: Joel Halpern <[email-masked]>
Date: Wed, 11 Nov 1998 17:35:54 -0500 (EST)

> No I was only referring to an NHC on a router without any NHS. 
If that NHC is a router, and you want proper reachability to arbitrariliy
connected things behind it,
    then it SHOULD (maybe even MUST) be an NHS, not an NHC.
Registration is NOT the right way to enter routing information into the
NHRP system.  NHRP Registration is for stable information.

An NHS is not that much harder than an NHC.  Particularly an NHS which
does not accept registrations (ie uses unnumber p-to-p links for the
default connectivity over ATM.)

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

---

From: Archana Nehru <[email-masked]>
Date: Wed, 11 Nov 1998 15:04:13 -0800

> NHRP system.  NHRP Registration is for stable information.

I am not clear why it is required that this NHC should also have an
NHS?. The subnet behind the NHC is a stable one since it is directly
connected to the NHC and the NHC is the only way to reach the
destinations in the subnet(no back doors).
My assumption is that there is a traditional routing protocol like RIP
etc running that maintians proper routing information at the NHS. The
registration is just to let the NHS know that for all the destinations
behind the NHC, NHC will terminate the ATM connection. How does it
disturb anything in the network?

-archana

---

From: Joel Halpern <[email-masked]>
Date: Wed, 11 Nov 1998 18:02:25 -0500 (EST)

> disturb anything in the network?
There are two cases.
Either there is a fixed set of subnets reachable directly behind the
device in question, or there is a toplogy back there.
In the first (fixed) case, it is acceptable, and maybe even desirable or
useful, top register the directly connected subnets.
On the other hand, if there is a topology back there, it is important that
routing know what is back there.  Then the border device is a router.
If the Border device is a router, using dynamic routing protocols to
decide what it removes from the ATM, then it had best be an NHS.
Note that an NHS which does not handle any ATM based subnets, and
therefore has no registrations, has a VERY simple job.  
The registration database of an NHS is supposed to reflect what is locally
reachable, not arbitrary topology beyond the ATM.

Yours,