[157119] in North American Network Operators' Group
Re: IPv4 address length technical design
daemon@ATHENA.MIT.EDU (Cutler James R)
Sat Oct 6 16:08:16 2012
From: Cutler James R <james.cutler@consultant.com>
In-Reply-To: <20592.31220.78712.550345@world.std.com>
Date: Sat, 6 Oct 2012 16:08:04 -0400
To: nanog@nanog.org
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
On Oct 6, 2012, at 2:35 PM, Barry Shein <bzs@world.std.com> wrote, in =
part:
>=20
> We can map from host names to ip addresses to routing actions, right?
>=20
> So clearly they're not unrelated or independent variables. There's a
> smooth function from hostname->ipaddr->routing.
I would suggest that this is a bit optimistic and oversimplified. =20
The mapping between DNS names and IP addresses is not necessarily unique =
or commutative. One may change either arbitrarily, as long some =
"directory service" exists which contains the current mapping. In =
addition, multiple DNS names may map to one or more IP addresses and IP =
addresses do not necessarily map to unique routes or DNS names. These =
are not smooth functions.
If names and addresses are not independent, then any change in either =
would predicate a change in the another. That is apparently not the =
experience of most network providers. The only action required for a =
change in network name or address is to update the "directory service" =
used to map between name and address.
> Is this a good use of DNS computrons? Answering DNS inquiries for
> every new connection for every single-routed host on the internet?
Yes, it is. Most "new" connections are repeats of previous connections =
(I request mail from my IMAP servers several times each day) and the =
preponderance of caching resolvers make the effort and traffic trivial. =
Even in the absence of cached final DNS reply, putting the lookup burden =
on the end system rather than the "routing engines" should be a =
no-brainer.
In particular, adding caching of connection destinations within routing =
components would not only seriously burden (read, slow down) routing =
engines but is also a violation of the Stupid Network. David S Isenberg =
said, "In a Stupid Network, control passes from the center to the edge". =
See http://www.isen.com/papers/Dawnstupid.html, originally published as =
the cover story of ACM Networker 2.1, February/March 1998, pp. 24-31.=20=
