Subject: RE: draft-ietf-ipngwg-site-prefixes

From: Richard Draves <[email-masked]>
Date: Mon, 17 Jan 2000 10:03:00 -0800

Reviving another old thread...

> -----Original Message-----
> From: Erik Nordmark [mailto:[email-masked]]
> Sent: Tuesday, December 14, 1999 9:35 AM
> To: Richard Draves
> Cc: Erik Nordmark; [email-masked]
> Subject: RE: draft-ietf-ipngwg-site-prefixes 
> 
> 
> > If for some reason the site-local address is not working 
> but the global
> > address does, won't it almost always be better to use the 
> global address?
> > Using the global address will only be a problem if there is 
> a renumbering or
> > some other event that effects the global prefix. So it 
> seems best to risk a
> > small chance of a future failure to prevent otherwise 
> certain failure in the
> > present.
> 
> I don't know.
> It has to do with the users' perception of the viability of 
> site renumbering.
> If we can make a statement that says "if you configure things this way
> then all site-internal communication will be unaffected by 
> site renumbering
> since it will always of site-local addresses" would that be helpful in
> convincing users that the risks associated with planned 
> renumbering (with
> overlap when both prefixes are valid) are acceptable?

I think with site-local addressing, site renumbering is VERY feasible.
Besides not breaking connections, if all the config files, databases, etc
within the site use site-local addresses, then they do not need to be
updated when the site renumbers.

So my view is, site-local addressing plus router renumbering gets us
practical site renumbering.

I still think it's good to keep the global addresses when returning
site-local addresses (putting site-local before global) - that's how I
implemented it. I think it makes the network more robust. For example, it
ameliorates a denial-of-service attack to keep the global addresses. If
somebody puts bad site prefixes on a link, you'll probably timeout trying to
connect to a bad site-local address. Instead of failing, the app can succeed
by trying the global address. 

This is sort of like the question of when/if deprecated source addresses
should be used when initiating communication.

Rich
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