OpenBSD IPv6 problem

[itojun@iijlab.net]

>> >         inet6 3ffe:80b0:1001:ff::3 -> 3ffe:80b0:1001:ff::2 prefixlen 127
>>                                                              ^^^^^^^^^^^^^
>> I believe the only prefixlengths Kame accepts for a gif tunnel are 64
>> and 128.
>Anyone know what's the rationale for allowing only those 2 values?  I can
>understand allowing the 64 but disallowing 127 while allowing 128 seems
>overly restrictive.  You do need to know there's at least 1 other on-link
>device on the same interface to setup BGP peering.  Otherwise it seems
>that in the case of a 128 prefixlength, one would need to do ebgp multihop
>as well as add a static route to the remote peer address, or in the 64
>prefixlength case, waste a SLA for the link?

	you should be okay to use 127 (never tested),
	as long as you do not specify the peer's address.

	the problem we see in "A B 127" (or 64) is ambiguity.

	let us assume that we have configured like "A prefixlen 64" (or 127).
	this lets you know that, on the interfrace, we have A/64 network
	and my address is A.  when we see some address under A/64, we throw
	it out to the interface.

	let us assume that we have configured like "A B prefixlen 128".
	this means that my side is A, and the other side is B.

	when we say "A B prefixlen 64" (or 127), we have A/64 network and the
	peer is B.  the information is ambiguous and affects neighbor
	determination.

itojun