> There has been a lot of discussion about the separation of identifiers > and locators (in various forms) on the multi6, ipv6 and ietf lists. > A lot of people seem to think this is in some form needed. > > I would like to know the arguments against such a change. nobody has worked out a complete solution. if you want to separate identifiers and locators you immediately need to build a reliable system to map between the two - where reliable means: fast, up-to-date, highly available, provides repeatable results across the entire network. for compatibility the identifiers need to be the same size as IP addresses, yet distinct from them. that way, apps just get identifiers rather than addresses from DNS lookups. ideally the mapping happens implicitly rather than explicitly - i.e. it happens as a side effect of an app treating an identifier as a destination rather than by having to send a query and wait for a response before transmitting the packet. also, you don't want to wait for the query to complete before sending packets - triangle routing and subsequent redirects are better. a lot of people think DNS names can be the identifiers, but besides being the wrong size, they're already too overloaded for that, plus DNS is too slow and not reliable enough. part of the reason that DNS is slow and unreliable is that it's too widely distributed. that and there are a lot of tricks being played with DNS that could get in the way. there are a lot of good ideas in HIP but it doesn't address the identifier-to-locator mapping problem. the closest thing we have to a working solution today is mobile IP, but purists tend to cringe when I say things like that in their presence. for stateful transport protocols we might be able to find a way to dispense with tunneling and let (e.g.) TCP operate in terms of the identifiers rather than the locators, even though the IP packets still contain the locators. summary of problems that need to be solved: 1. security 2. fast, robust, highly available identifier-to-locator mapping layer 3. arranging for hosts (or perhaps routers) to find the mapping layer for a particular identifier 4. delegation and assignment of identifiers 5. making transport protocols work in terms of identifiers rather than locators while minimizing overhead technically, I think it's doable. whether we can actually agree on a solution is a different question. Keith