[Softwires] Softwires configuration via DHCP

["David W. Hankins" <[e-mail]>]

In forming the DHCPv6 option format for Softwires configuration, I
made a few assumptions.  I would like to (hopefully _very_ briefly)
explain my rationale, and invite additional feedback before I revise
the draft.

1) That the only configuration required would be the endpoint - that
   the 'Softwires Protocol' would include as specification a single
   kind of tunnel, for example.  The presumption, for simplicity, is
   that any Softwire client can establish a connection with any
   Softwire service without needing to know "which type."  Put another
   way, all Softwire services will be externally identical.

2) That only a single endpoint is sensible.  That there wouldn't be
   a configuration where a client had multiple Softwire endpoints
   configured at once (migrated from one to another, but never
   straddling two or more at once).

3) That although many current tunneling software implementations might
   accept domain names as configuration parameters,

	a) A recursive domain name lookup after completing DHCP is
	   extra work for no benefit.  DHCP servers can and will
	   perform the lookup on behalf of the client.  These extra
	   packet exchanges are trivial, until every packet you transmit
	   drains your phone's battery.

	b) Tunneling is a "routing kind of service", and so my first
	   inclination is that operators are likely to solve tunnel
	   endpoint reachability problems ("failure modes") by using
	   classic IP routing solutions.  Consequently the
	   configuration of interest is an IPv6 address, whose
	   termination may change through changes in routing policy.

These are essentially the assumptions that went into
draft-dhankins-softwire-tunnel-option-01.

-- 
David W. Hankins	"If you don't do it right the first time,
Software Engineer		     you'll just have to do it again."
Internet Systems Consortium, Inc.		-- Jack T. Hankins