Subject: Re: [lisp] Comments about the LISP header

From: [email-masked] (Noel Chiappa)
Date: Thu, 28 May 2009 11:16:53 -0400 (EDT)

> From: Margaret Wasserman <[email-masked]>

    > a well-defined way to change the headers later if that is necessary.

I've been thinking _very_ hard, for some years now, about making sure LISP is
'developable' (i.e. it can change and grow in a way that is both reasonably
easily interoperable with installed base, but without putting limits on where
we can go). 

Q.v. my big go-round with Sam at charter time about whether or not adding
'hooks' for future enhancements was in-scope. So I am _more_ than sympathetic
to your goals. Having said that...

    > I do think it makes sense to add a version number field to the LISP
    > data header

I'd thought about that, but I think using a different UDP port would do the
same thing, and without overhead.

If we ever define a LISP-specific data carriage protocol, a version number
might be useful there, but such a prototocol is out-of-scope for the WG for
the moment (and I see no pressing reason to bring it in-scope).

    > and to all other LISP headers

Again, I'm not sure that a version-number brings us much. There is already an
ability to add new control-types, and if we change the syntax on any control
message, or add new ones, we can do it that way. And again, there's always the
'different UDP port' technique...

	Noel

---

From: Margaret Wasserman <[email-masked]>
Date: Thu, 28 May 2009 11:45:59 -0400

> same thing, and without overhead.

I agree that using a different UDP port for extensibility would be  
better, if that option is available.  It has been my understanding,  
though, that using additional UDP or TCP ports for extensibility is  
"frowned upon", because of concerns that the TCP/UDP port numbers  
space is limited.  I can't find any actual documentation to that  
effect, though.  So, if we think that using additional UDP ports would  
be the best extensibility mechanism for LISP (which I could be  
convinced that it is), I think we should just make a note of that in  
the spec.

> 'different UDP port' technique...

I can live with that, assuming we document this as our plan for future  
modifications/extensibility.

Margaret