>actually, it turns out that it is possible to make an unnumbered
>interface using gre(4) (the remote address is set using the greconfig(8)
>program which uses an ioctl specific to the gre device). an equivalent
>configuration using IPPROTO_IPV[46] does not seem to be possible with gif(4).
>the obsolete ipip(4) did, on the other hand, support unnumbered links.

	i don't understand what you mean by "unnumbered interface" here.
	could you elaborate? (for instance, greconfig command line examples?)

itojun