Re: LL70: Use of the term "valid"

> From: "Peter Johansson" <[email protected]>
>=20
> >The validity of a configured address is difficult to establish =
because the=20
> >context in which it is intended to operate or becomes invalid can =
vary.=20
> >Therefore I think that all we can do is explain the concept and =
present=20
> >the DNAv4 reachability test as a useful example (informative) rather =
than=20
> >a definition (normative) of validity.
>=20
> Sounds like a good idea to me---but do it in the context of "routable" =

> rather than "valid".
>=20

The term "routable" is clearly defined:

   "This document uses the term "routable address" to refer to all
   unicast IPv4 addresses outside the 169.254/16 prefix, including
   global addresses and private addresses such as Net 10/8 [RFC1918],
   all of which may be forwarded via routers."

"configured" is not explicitly defined but I would assume that if I type =
"ifconfig eth0 5.6.7.8" then I have "configured" that address. =
Similarly, if DHCP has handed me the address 5.6.7.8 and my lease is =
still valid then that address is configured and because it conforms to =
the definition above it is a "configured routable address".

This tells me nothing about whether the address can be successfully used =
in any way. The useability of an address depends largely on the routing =
tables of other hosts on the same link and/or on the accessibility of =
routers which will recognise the presence of the address and route =
traffic to and from it. The reachability test of DNAv4 is a quick but =
rough test of the second part of this.

As Bernard pointed out - if the default router is down it doesn't mean =
that an address is totally unuseable - it may still work fine for =
communications which are on-link or via other routers.

On the other hand, if I have the "configured routable address" 5.6.7.8 =
but am sitting on a network 200.0.0.x many hops away from my default =
router and with no other local hosts aware of my presence then 5.6.7.8 =
will not be useable and for now I would be better off with a LL address.

The term "valid" could possibly be replaced with "useable" or "working"  =
but is not redundant.

Philip