Destination Prefix Extension

[Yakov Rekhter <[e-mail]>]

Folks, 

Could someone give a good technical reason(s) to express Destination
Prefix Extension as mask (rather than a length of a prefix) ?

Yakov.

P.S. Expressing it as a prefix length would (a) avoid the need to
check for non-contiguous mask, (b) enable to use the same
option for multiple network layer protocols (e.g. IPv4 and IPv6),
(c) provide more compact encoding, and (d) be more consistent with
the notion of "address prefixes".