using "reserved" IPv6 space

Tue Jul 17 04:11:18 UTC 2012

On Jul 16, 2012, at 12:39 PM, Oliver wrote:

> On Monday 16 July 2012 18:26:08 Rajendra Chayapathi wrote:
>> On the HSRP/ND part , this all falls in the First Hop redundancy areana
>> and can be achieved via any of the following and each has its merits and
>> cons..
>> 
>> 1) Using ND -- need to tune the "IPv6 nd reachable time" to achieve the
>> faster failover
>> 2) Using any of the First hop redundancy protocol ( HSRP, VRRP , GLBP)
>> 3) Default route selection.
>> 
> 
> In all honesty, I think using ND as the failover method is a generally bad 
> idea - you have no way of ensuring all endpoints take note of or honour the 
> router preference flag.

Huh? Any host which doesn't is provably buggy. I'm not saying it can't or won't
happen, but, seriously? If the host is that buggy, you can't count on it using
the fake MAC either.

> Additionally, having a 1 second validity lifetime is going to create a lot of 
> ICMPv6 spam across the segment - big deal? perhaps not. But when contrasted 
> with the fact that it can be wholly avoided using one of the aforementioned 
> redundancy protocols, why would you do it?

You don't need a 1 second valid timer (that would be absurd). You need a
1 second keep alive (if you really care about 1 second fast fall-over) and you're
going to get just as much SPAM with sub-second fallover from any of the other
solutions as well. They all send multicast packets.

> Additionally, as an alternative to RAs, you can simply point default at the 
> all-routers anycast address.

The disadvantage to this is the high probability of packet duplication. For
someone worried about ICMP spam on the subnet, I'm surprised you're not
worried about what happens when 2 or more routers copy the same packet
and route both copies on to the end destination. (Lather, rinse, repeat said
duplication for any upstream segments using such tactics as well).

Owen