Subject: (IPng 6991) RE: route distribution via ND

From: Marc Fiuczynski <[email-masked]>
Date: Wed, 30 Dec 1998 10:33:51 -0800

>From: Thomas Narten [mailto:[email-masked]]
>Sent: Wednesday, December 30, 1998 5:17 AM
>To: Richard Draves
>Cc: 'IPng List'; 'Marc Fiuczynski'
>Subject: Re: (IPng 6964) route distribution via ND 
>
>
>> The basic problem we want to solve is letting routers
>> inform hosts about routes. For example, we don't want
>> to manually configure hosts to know that a certain v6
>> prefix should be routed to Marc's v6-v4 translator.
>
>Note that the need to have prefix routes installed in
>hosts is only necessary if the host has multiple interfaces
>(i.e., is multihomed). If there is just one interface,
>using a single default route and redirects will handle 
>everything just fine.

Just so that I am crystal clear about this.  What should happen for the
following simple scenario:  

Clients sending packets with a prefix P
*must* be sent via a stub-router S.  

This stub-router may not have the capability to act as a default router.
The question is how do clients learn about the route for prefix P to
stub-router S?

One approach is to have a default-router send redirects.  What if there
is no default router in this particular environment?  Another approach
is to distributed routes via RIP.  What if the clients are too primitive
(e.g., an IPv6-capable embedded device)?  Our approach is to use the
existing ND support to distribute simple routes for particular prefixes
using the prefix information option.

Marc

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From: Robert Elz <[email-masked]>
Date: Thu, 31 Dec 1998 13:12:08 +1100

Date:        Wed, 30 Dec 1998 10:33:51 -0800
    From:        Marc Fiuczynski <[email-masked]>
    Message-ID:  <[email-masked]>

  | This stub-router may not have the capability to act as a default router.

It would not be much of a router, but let's leave that aside.

  | The question is how do clients learn about the route for prefix P to
  | stub-router S?

From some other router, via a redirect, or via RIP, most likely.

  | One approach is to have a default-router send redirects.  What if there
  | is no default router in this particular environment?

"Default router" is a misnomer, "default" is not a property of the router,
it is an attribution provided to it by the host.   Any router that is truly
a router should do.   If there is only S (it is the only router), then it will
do (must do) - regardless of what it might do to packets sent to it with
unknown addreses.   If there is some other router, then it will suffice.
If you are postulating an environment with some number (> 1) of brain dead
semi-routers, that can't really route, but do forward some packets, then
I think that is an environment that we ought to explicitly discourage (and
certainly not fudge any protocols to support).

  | Another approach is to distributed routes via RIP.

Yes, that one works well.   I have been using RIP that way for years
(routing is done via OSPF, hosts, most of which of significance here
are multi-homed, learn what exists where by listening to RIP.

[Aside to Bill Manning: see rfc2080]

  | What if the clients are too primitive
  | (e.g., an IPv6-capable embedded device)?

It is hard to imagine a device too primitive to support receive only RIP.
It is certainly no more complex that supporting the same functionality in
ND packets.   Certainly there might be a little extra packet recognition
logic involved, but this is really on the side of being so trivial as to
be not worthy of mention.

kre