>If size is a concern, how about using a union and a flag bit?
>(if the flag is clear, use the rcvif arm of the union; if set, use the
>sndso arm of the union).

	mbuf flag bit is also very important resource; we may want to
	increase it to 32bit some day.

>One other note.. it occurs to me that a complete policy engine may
>also want to know the receiving interface for forwarded packets, so
>keeping the old value around might make sense.

	That would be possible.

itojun