(usagi-users 01015) Re: Scoped Addresses

[Bernd Walter <ipv6@xxxxxxxxx>]

On Mon, Nov 12, 2001 at 08:20:28PM +0000, Ben Clifford wrote:
> On Mon, 12 Nov 2001, Bernd Walter wrote:
> 
> > If you are connecting networks with unco-ordinated addresses you are
> > calling for troubles.
> 
> But this is what happens with link-local addresses.

Link local address are automaticaly co-ordinated.

If you receive a connect - how would you know on which interface to
send the answer back?
OK - you can remember the interface from which you got the request, but
this requires symetric routes.
With link local you know for shure its symetric because it came via a
direct connection.
With site local you never know.

> > IP Packets should never leave their area of validity which is what
> > you are doing in your example.
> 
> I am not suggesting routing packets from one site to another - I am just
> saying that a particular machine may be connected to multiple sites
> (without routing packets between those sites).

Well site local addresses are defined to be fec0::/10.
Lets say each site has enough with /48 and the leaving 38 bits are
filled with a site specific random value.
If you are ever in need to connect to another site you have a
(2^38)-1 : 1 chance that you don't collide.
If you don't do you shouldn't be surprised some day.

After all you can always renumber.

If you are in need for such a hack it's a good sign for a bad network
design.
The correct answer is to fix the bad design instead of working around.

-- 
B.Walter              COSMO-Project         http://www.cosmo-project.de
ticso@xxxxxxxxx         Usergroup           info@xxxxxxxxxxxxxxxx