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