Re: ping-pong phenomenon with p2p links & /127 prefixes

[Fred Baker <fred@cisco.com>]

On Aug 23, 2010, at 1:15 PM, Joel Jaeggli wrote:

> On 8/23/10 5:11 AM, sthaug@nethelp.no wrote:
>>> These mechanisms are applicable to any type of link, would preserve the
>>> simplicity of universal 64 bit IIDs and the other benefits of them e.g.
>>> CGAs, as well as avoiding the ping-pong problem.
>> 
>> IMHO, the "universality" of 64 bit IIDs went down the drain the moment
>> router vendors allowed longer than 64 bit netmasks to be configured.
>> 
>> For the routers I am most familiar with (Juniper, Cisco), longer than
>> 64 bit netmasks have been configurable for many years. And such masks
>> are heavily used for provider backbone links.
>> 
>> The IPv6 standards community can of course continue to pretend a belief
>> in universal 64 bit IIDs - thus ensuring that they are out of touch
>> with IPv6 reality...
> 
> I think it can be demonstrated that reality includes longer prefixes
> than /64. The document needs to be unequivocal about that fact. or more
> to the point that it is altering that specifications as they stand now.

I agree, but I think I would phrase it differently. The point is that an IPv6 address is a CIDR prefix with an interface ID. As allocated by SLAAC, it will be a /64 prefix and a 64 bit IID. But SLACK is not the only allocation paradigm. Addresses that are allocated by other paradigms are not bound by the SLACK paradigm, only by the need to perform and respond to duplicate address detection and as a result guarantee the local uniqueness of the IID.