IPv6 Deployment for the LAN

bmanning at vacation.karoshi.com bmanning at vacation.karoshi.com
Thu Oct 22 11:30:19 UTC 2009

On Thu, Oct 22, 2009 at 10:18:48PM +1100, Karl Auer wrote:
> On Thu, 2009-10-22 at 11:08 +0000, bmanning at vacation.karoshi.com wrote:
> > On Thu, Oct 22, 2009 at 09:44:38PM +1100, Karl Auer wrote:
> > > On Thu, 2009-10-22 at 10:30 +0000, bmanning at vacation.karoshi.com wrote:
> > > > > The RA contains a preference level... maybe that doesn't cut it if
> > > > 
> > > > 	I point you to a fairly common Internet architecture artifact,
> > > > 	the exchange point...  dozens of routers sharing a common
> > > > 	media for peering exchange.  
> > > 
> > > And how do they discriminate now, with IPv4?
> >
> > 	IPv4 has no concept of RA/ND.  to make this construct work at
> > 	all in IPv6, all participants have to turn -off-  RA/ND to prevent
> > 	one or more routers trying to impose their views of addressing
> > 	on their neighbours.
> But my question was not about IPv6. How do IPv4 routers operate in such
> a situation?
> Regards, K.

	exchange design 101.

	each connecting router interface is manually configured with an
	address of the exchange fabrics IP space.

	to establish peering, a router needs to know, at a minimum, the targets
	IP address and ASN - and while arp (if enabled) can get the target IP address,
	the ASN has to come via another channel - usually manually aquired.

	this is how the exchanges generally work, regardless of IP address family.

	more generally, where there are two or more egress routers from a broadcast
	domain, there will be problems -if- the routers know about each other -and-
	have the ability to try and set the exit rules for all other participants
	sharing the broadcast domain.  Hence, with IPv6 and RA/ND, the idea of 
	"preference" levels ... although in most cases I've experienced where there 
	are multiple exit routers - that doesn't work either, since only subsets of 
	the nodes on the shared media can use one or the other egress router.  e.g.
	all the nodes don't fate-share.

	RA/ND was only an 80% solution anyway.  

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