Re: I-D ACTION:draft-ietf-v6ops-nap-01.txt

[Stig Venaas <Stig.Venaas@uninett.no>]

On Mon, Jun 27, 2005 at 06:22:17PM +0930, Mark Smith wrote:
> Hi,
> 
> On Sat, 18 Jun 2005 01:18:42 +0930
> Mark Smith <ipng@69706e6720323030352d30312d31340a.nosense.org> wrote:
> 
> > Hi,
> > 
> > "6.2  Subnet topology masking
> > 
> >       There really is no functional gap here as a centrally assigned
> >    pool of addresses in combination with host routes in the IGP is an
> >    effective way to mask topology. "
> > 
> > I'm wondering if the above is actually the case. 
> > 
> > I think host routes are easy enough to understand from the point of view
> > of propagating /128s around within an IGP. 
> > 
> > What I'm curious about is how the end-nodes are configured and how they
> > operate, in particular when they are attached to a broadcast
> > multi-access link e.g., an ethernet. Has this operation been discussed or
> > described in an ID or RFC that I'm not aware of ?
> > 
> 
> It looks like a /128 prefix length is not permitted on an interface,
> according to draft-ietf-ipv6-addr-arch-v4-04.txt, which I think means
> most of the issues I was concerned about described disappear.

You're refering to 2.5.1 where it says

   For all unicast addresses, except those that start with binary value
   000, Interface IDs are required to be 64 bits long and to be
   constructed in Modified EUI-64 format.

I guess. I can't say I like this. I believe it's quite common in IPv6
to use /128 for addresses on loopback interfaces on routers and inject
those into IGP (just like IPv4 /32). If I understand this correctly,
one would then be forced to use a different /64 for each router loopback.
It's also pretty common to use a longer than 64 prefix for tunnels, e.g.
/126.

Is strictly speaking an interface identifier always needed? As it says
in 2.5.1 it's used to identify interfaces on a link, but for loopback
there isn't really any link... You wouldn't need to do ND etc for the
loopback addresses.

> I'm still not sure exactly how host routing would work from the
> end-nodes point of view, so I'll continue to do some reading. It seems
> to me that hiding the network or subnet topology by not grouping IPv6
> addresses according to their common data links means that the subnet bit
> portion of the address loses its significance when determining whether a
> destination address is off or onlink, during Neighbour Discovery.

The way I see it the hosts would have physical interfaces connected to a
physical link and have addresses for those doing ND etc as usual. In
addition they would have some kind of virtual interface with some /128
addresses and somehow inject host routes for those on the physical
interfaces so that next-hop would be the (e.g. /64) addresses on the
physical links. This is how I believe it works today when you use
loopbacks with /128 for routers.

Stig

> 
> Thanks,
> Mark.