IPv6 issue on TestBot?

Ben Peddell klightspeed at killerwolves.net
Thu Sep 22 09:08:02 CDT 2011

On 22/09/2011 9:43 PM, Per Johansson wrote:
> 22 sep 2011 kl. 12:14 skrev Michael Stefaniuc:
>> Wow! /66? And that works? While the standard allows for that you "should
>> use /64" which everybody and his dog read it as that is the only thing
>> that needs to work and the only thing that get tested. IPv6 brings back
>> the class-full thinking which everybody has to painfully unlearn once
>> IPv6 catches on...
>> "Safe" prefix length (especially if involving client devices) are:
>> /64 - LAN
>> /126 and /127 - point to point
>> /128 - host routes
> RFC3513 is quite more strict than "should":
>    All global unicast addresses other than those that start with binary
>    000 have a 64-bit interface ID field (i.e., n + m = 64), formatted as
>    described in section 2.5.1.  Global unicast addresses that start with
>    binary 000 have no such constraint on the size or structure of the
>    interface ID field.
> (2001:: has the binary prefix 001). So this might very well be the problem.

If I understand that correctly, if the interface has a hardware address
(48-bit MAC or 64-bit EUI), then the interface ID should be constructed
from that address.

Of course, if you are the administrator of the 2001:888:2000:38::/64
block, then you can assign Scope-Local Interface IDs as you see fit,
just as everyone else does, and as allowed in RFC3513 2.5.1 - however,
the RFCs say the subnet mask needs to be /64.

Ben Peddell
IT Support Bowen, Collinsville, Proserpine and Home Hill Catholic schools

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