At Mon, 20 May 2013 10:18:21 -0400, John C. Klensin wrote: > > This is not my primary (or even secondary) area of expertise > but, given that the RR space is not unlimited even though it is > large, wouldn't it be better to have a single RRtype for > IEEE-based EUIs with a flag or other indicator in the DATA field > as to whether a 48 bit or 64 bit identifier was present? Short answer: Probably not, but it depends on the application. Longer answer: See RFC 5507.