> > in general the only way for node A to determine whether node B > > is reachable is for A to send a packet to B. if A gets a reply > > from B, B is reachable. if A gets an ICMP message back, B > > is not reachable (for temporary or permanent reasons). if A > > gets nothing back, either B is (temporarily) unreachable or > > B doesn't want to answer A. > > > > but you'll never be able to determine this by looking at prefixes. > > Actually, the "Default Address Selection for IPv6" draft includes > language of that nature.
well, there are lots of things wrong with that document. and no, an app can't reasonably assume that B is reachable from A even if they're both within the same site. and there are probably situations where a "non local" address (i.e. one with a shorter matching prefix) is preferable to a "local" one, because prefix length tells you nothing about available bandwidth, reliability, delay, jitter, or policy. -------------------------------------------------------------------- IETF IPng Working Group Mailing List IPng Home Page: http://playground.sun.com/ipng FTP archive: ftp://playground.sun.com/pub/ipng Direct all administrative requests to [EMAIL PROTECTED] --------------------------------------------------------------------
