On Tue, 3 Jun 2003, Andrew White wrote: > > I hope you're not implying that apps should know the difference between > > the two? That would be broken. The host probably could, though. > > In most situations, an application would not be required to know the > difference between the addresses, relying on correct behaviour of > gethostbyname (destination address selection) and source address selection. > > However, certain applications may wish to deliberately operate at a certain > scope (such as those doing ip address referrals between hosts which have > local and global addresses and those which only have global addresses) and > these would need to override the default address selection rules, thus being > conscious of address scoping.
Yes, applications should of course be *able* to influence these, if they desire so, provided that: - they don't need to if they don't want to (including multi-party apps) - the API is de-facto standardized so every app doesn't have to reinvent the wheel for 10 different operating systems > > I think a better method would be to give preference to global unicast, > > ie., reverse the scoping rule to prefer the greatest scope. > > On what grounds? Local scoped addresses are not mandatory, and thus should > only be put in place if they are intended to be used. Yes, but used by *WHOM* ? If they're used in the site, and that only, typically that would be OK. This also begs the question whether local-scoped addresses would be deployed without global addresses or not (as some have required). If there are local-only nodes, the reason to deploy local-scoped addresses could be simply to use them when needed, no more no less -- without disturbing the global communication of nodes with global addresses! > To my way of > thinking, the presence of a locally scoped address suggests that the network > is unwilling to trust the global address for local communication, The motivations vary a lot. > and would > thus expect the local address to be preferred for local-local traffic. That may be a desire, yes, but they may be others -- particularly regarding how you intend to deploy the addresses. To me, by default using the global addresses would seem like a plus: even if/when they leak (to a site which is also using local addresses), nothing bad happens: the global addresses are still tried first (and not second) -- the way it should be. This way, people could also publish local addresses in the non-split DNS (whether that's a good or bad thing is a different issue). > > > However it is useful if a host can have both types of addresses > > > and use them appropriately. This creates a host with multiple global > > > addresses, a form of multihoming. > > > > I fail to see how a local and a global address could be considered a form > > of multihoming. > > It depends on your definition of multi-homing. I've hear the term used in > the following ways: > > - A network with access to the global internet via more than one independent > path. In some cases, it's more detailed than that, but yes. > - A node with more than one usable address (having addresses in more than > one logical subnet simultaneously). This is an abuse of the term. > The second definition is being referred to above. That's "multi-addressing". (Note that there's a significant overlap with the two definitions above.) -- Pekka Savola "You each name yourselves king, yet the Netcore Oy kingdom bleeds." Systems. Networks. Security. -- George R.R. Martin: A Clash of Kings -------------------------------------------------------------------- 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] --------------------------------------------------------------------
