[154929] in North American Network Operators' Group
Re: using "reserved" IPv6 space
daemon@ATHENA.MIT.EDU (Jimmy Hess)
Tue Jul 17 02:17:12 2012
In-Reply-To: <1342502946.6281.164.camel@karl>
Date: Tue, 17 Jul 2012 01:16:32 -0500
From: Jimmy Hess <mysidia@gmail.com>
To: Karl Auer <kauer@biplane.com.au>
Cc: NANOG List <nanog@nanog.org>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
On 7/17/12, Karl Auer <kauer@biplane.com.au> wrote:
[snip
> I'm not sure I follow the logic there. If the anycast router changes the
> packet will be resent to the new subnet anycast router eventually
> (assuming some layer cares enough about the packet to resend it). The
> "last known hardware address" doesn't matter any more or less in this
> scenario than it does in any other routing situation.
The pertinent discussion is not about "any other routing situation";
it's about first hop redundancy.
The "last known hardware address" is in the NDP table, so the packet
retransmissions likely wind up in the same place
Another problem is the subnet anycast address may find unwanted
routers that have to listen on it, including routers with only one
interface and incomplete routing info, and including some
unauthorized 5-port IPv6 router someone smuggled into the
building and plugged in somewhere.
By contrast, a real FHRP that implements failover either uses a
virtual hardware address, or a 'gratuitous arp' type mechanism, so
the packet retransmissions will go to the live failover partner.
--
-JH
