using "reserved" IPv6 space

Owen DeLong owen at
Tue Jul 17 06:44:42 UTC 2012

On Jul 16, 2012, at 11:16 PM, Jimmy Hess wrote:

> On 7/17/12, Karl Auer <kauer at> 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

NUD should actually take care of that.

> 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.

The whole concept of gratuitous arp is strictly IPv4.


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