Re: Stupid Ipv6 question...

["Kevin Oberman" <oberman () es net>]

> Date: Fri, 19 Nov 2004 10:11:36 -0800
> From: Crist Clark <crist.clark () globalstar com>
> Sender: owner-nanog () merit edu
>
>
> Lars Erik Gullerud wrote:
>
> > On Fri, 2004-11-19 at 16:36, Stephen Sprunk wrote:
> >
> >
> > > /127 prefixes are assumed for point-to-point links, and presumably an 
> > > organization will divide up a single /64 for all ptp links -- unless they 
> > > have more than 9,223,372,036,854,775,808 of them.
> >
> >
> > While that would seem logical for most engineers, used to /30 or /31 ptp
> > links in IPv4 (myself included)
>
> Aren't most engineers used to the fact that point-to-point links are
> not broadcast links and therefore the concept of a network/netmask for
> the interface is somewhat useless? In addition, link-local addressing
> eliminates many situations where you need to allocate tiny blocks for
> p2p links.

Just to introduce a touch of practicality to this discussion, it might
be worth noting that Cisco and Juniper took the RFC stating that the
smallest subnet assignments would be a /64 seriously and the ASICs only
route on 64 bits. I suspect that they influenced the spec in this area as
expending them to 128 bits would have been rather expensive.

In any case, if the prefix length is >64, routing is done in the
CPU. IPv6 traffic for most tends to be light enough that this is not a
big issue today, but the assigning /126 or /127s for P2P links is
really, really not a good idea. the use of 127s also ignore the
possibility of a anycast address.
-- 
R. Kevin Oberman, Network Engineer
Energy Sciences Network (ESnet)
Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab)
E-mail: oberman () es net                       Phone: +1 510 486-8634