>There's the question of how much burden do scoped addresses create for >applications. For most applications, even on multi-sited hosts, there's >no burden at all if they are coded using sockaddrs. Distributed >applications that send around addresses do have to cognizant of scoped >addresses. However this is not hard to deal with. For example I checked >on how one such distributed application that is being built at MS >handles this issue. The application looks at the scope of the >correspondent and sends its addresses of matching scope. In other words, >when talking to a global address you send your global addresses and when >talking to a site-local address you send your site-local addresses.
application on multi-sited host is difficult, as - not every protocols are friendly with scoped addresses (scope identifier get stripped off during transit) - even if you successfully pass around scoped addresses with scope identifiers, scope identifiers (view of scope) differ by node. >There's the question of implementation effort for the network stack to >support scoped addresses. This is hard to quantify but I would say it >was small. (And necessary regardless of site-locals, unless link-locals >are next up for revisionist architecture.) The additional code in source >& destination address selection was about 10 lines each. The additional >code in route lookup and destination cache management was worse, maybe >100 lines. A scope-id needs to be passed around as an argument to >various functions so there was a very small impact in many other places. i would comment that it is very hard to get multi-sited router implementation right (specifically routing protocols). see descriptions by NEC guys a couple of months ago - it is a big mess. so my take is as follows: - we should at least forbid nodes from joining multiple sites. it will simplify things a lot. - we should document behavior of site-border routers, every gory details. this is the bottom line. i'm still a bit concerned about the use of scoped address in general, as it will cause confusion when scoped address leaks out of site in application payload (like email foo@bar@baz notation or whatever). but i feel it too late to kill it. itojun -------------------------------------------------------------------- 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] --------------------------------------------------------------------