On Apr 20, 2007, at 19:33, Tony Hain wrote:
I have been arguing for a long time now that we should be following the 3484approach of 'smallest scope' by default (and I use the term scope withintent). For example, there is no reason a printer should bind to anything but a ULA prefix by default. I have heard complaints that the API does not allow a service to register for a specific prefix range like ULA, but I have not followed up to check that. While I understand that the app developerdoes not want to worry about issues like scope, in the real world the network is managed with scopes where policy is applied. Frequently the addressing allocation aligns with those policy scopes, and can be specifically forced to align when traffic needs to traverse a policy enforcement point.
I thought we only had two unicast address scopes at this time: link- local scope and global scope. (Okay, three if you count the deprecated site-local scope, but I don't.) ULA's are global scope with limited reachability. The API already permits applications to enumerate the addresses assigned to an interface. They can bind to addresses explicitly rather than use wildcard binding.
Now is probably a good time for me to repeat my long-running refrain that OS implementations should permit system administrators to configure interfaces to ignore advertisements of global scope prefixes other than ULA prefixes. I think this would help a lot over the short term.
Over the long term, I worry that something hideous will be required by the people who get paid lots of money to establish complicated functional requirements, and nobody but twelve-fingered post-human Martians will be able to manage which services are available in what regions of the Internet.
-- j h woodyatt <jhw@apple.com>