[RRG] On identifiers, was: Re: Does every host need a FQDN

[Iljitsch van Beijnum <iljitsch@muada.com>]

On 12 aug 2008, at 19:01, Scott Brim wrote:

> > And don't MIPv6, SCTP and TCP-over-shim6 all use regular IP  
> > addresses that come with locator functionality as their ID?

> You want something that is stable despite changes in topological  
> location.  As Brian says, MIP uses the home address as an identifier  
> -- an anchor point for authentication.  I don't know mobile SCTP or  
> shim6 very well (help?) but they seem to use a similar stable anchor  
> point. It seems that none of these use a pure network layer  
> identifier.

I was talking about SCTP and TCP-over-shim6 in a multipath transport  
context (although neither are capable of using multiple paths  
concurrently at this time), not a mobility context. SCTP manages  
multiple addresses, I don't think any of them are special or stable.  
shim6 uses the addresses used by the upper layer (such as TCP) as the  
stable identifier, but it also requires these addresses to be working  
locators at the time the shim6 capability is negotiated and other  
locators are exchanged.

Let's inventory what we need identifiers for:

1. demultiplexing
2. access control
3. error detection
4. referrals

And what we need locators for:

5. forwarding packets
6. sending back control messages

Note that all of these uses of identifiers can be limited to the  
application or session layers so there is no need for identifiers to  
appear in any layer 3 or 4 headers - if we don't mind changing  
applications and APIs to map application layer identifiers to  
transport and lower layer locators.

But changing applications is a non-starter, because the number of  
applications is so huge and application writers simply lack the  
knowledge to interact with the network properly. After 10 years there  
are still applications that don't know how to work over IPv6, for  
instance.

Now NOT changing applications means that the identifiers must look a  
lot like regular IP addresses. With shim6, we avoided a mapping system  
at significant cost: we need assistence from applications when the  
initially chosen identifier is not currently a reachable locator.  
Also, shim6 feedback indicates that a pure host solution is not what  
most people want, and requiring changes on both ends is a big  
deployment barrier.

If we want to do all of this in middleboxes we pretty much end up in  
LISP territory. The data plane issues with that are fairly well  
understood by now, but this requires a identifier-to-locator mapping  
service, which is not that well understood currently.

Do we have consensus yet on what would be the best place to solve the  
problem?

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