(usagi-users 00551) Re: routing / redirect messages

[Nathan Lutchansky <lutchann@xxxxxxxxxx>]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

On Thu, 24 May 2001, Remco van de Meent wrote:

> On this network, we have one big /64 prefix. However, some of the hosts
> in this network want to act as a router for other (small) network
> connected to it. These networks will get a /112 out of the /64 range.
> The default router knows which /112 is network via what host (router).

First of all, this is a really, really bad idea since it breaks the
topology assumptions of unicast addressing in IPv6.  It will also make
administration of your network a bit more difficult, since all the hosts
on the little tiny networks will have to be manually configured.  You
would be much better off if you simply gave a /64 to each router on the
subnet.  It's not like IPv6 has limited address space.

That said, here's how to do it...

> I'm currently looking for a solution to this problem. I've been
> thinking of using neighbor discovery redirect messages, sent out by the
> default router, when a host in the /64 network is trying to reach a
> host in one of the /112 networks.

There's no reason this wouldn't work.  There's two ways to do it.

First, you can configure the little routers to respond to neighbor
solicitations for stuff inside their /112 block with proxy advertisements.
Kinda like proxy ARP in v4.  This is allowed in the spec, but I'm not sure
how you configure it.

Second, if you have control over the router sending the router
advertisement messages, you can turn off the "on-link" flag for that
prefix.  If you're using radvd on Linux this is the "AdvOnLink" flag.
This will cause hosts on the subnet to send all packets for that subnet to
the default router, which will then issue a redirect to either the
destination host if it is directly on the subnet, or to the little router
if the destination is on a little network.  I've never tried this, but
that's how it's supposed to work.  -Nathan

- -- 
+-------------------+---------------------+------------------------+
| Nathan Lutchansky | lutchann@xxxxxxxxxx |  Lithium Technologies  |
+------------------------------------------------------------------+
|  I dread success.  To have succeeded is to have finished one's   |
|  business on earth...  I like a state of continual becoming,     |
|  with a goal in front and not behind. - George Bernard Shaw      |
+------------------------------------------------------------------+
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.0.4 (GNU/Linux)
Comment: pgpenvelope 2.10.2 - http://pgpenvelope.sourceforge.net/

iD8DBQE7DUzlTviDkW8mhycRAo7mAJ4pC9x9YSbJ4/5Zy7/Gn7Vz9iNW5wCcCK/3
CHpPBXxagUL/IYUk57Ia0Pw=
=f6BL
-----END PGP SIGNATURE-----