Joe Geiser writes:
>As for resolving and routing - they do provide secondary DNS for us
>(they'll do primary for their customers by default, unless you specify
>otherwise), but if I need to resolve an address that they don't route -
>there's always those root servers in your CACHE file under DNS...they're
>god (note the little "g") - they know everybody :-)  (at least it seems
>so).  I've never had a problem getting routed to a node I needed to get to...
 
There seems to be some confusion between resolving and routing. They're
two completely different things; routing is not at all dependent on
resolving, and it's also possible (at least theoretically, if not
practically) to resolve without routing. Since it's easiest to explain
with pictures, I'll try to put something up on our web site over the
weekend -- Robelle's web site, uncharacteristically, doesn't seem to
address (sorry) this issue. Meanwhile, I'll try an analogy.
 
Suppose that you want to visit a long-lost friend, whom you've just
learned lives in a distant city. (The following assumes that you're male,
and therefore don't want just to call them and ask for directions. If
you're not male, assume that your friend's phone isn't working.)
 
The first thing you need to do is find their address. You happen to have
a telephone book for the city they're in, so you look up their name and
find their address. This is resolving: given their name, you've found
their address. If you hadn't had a phone book (a "hosts" file), you would
have visited (if male) or called and asked (if not) the local library, to
get the information from the copy of the phone book they have in their
collection. In other words, you would have used a Domicile Name Service,
or DNS.
 
Once you have the address, you have to get there. The first thing you do
is send yourself to your default gateway, which is probably the local
airport. At the airport, you examine the flights available (the routing
table), send yourself through the gate (port) for the city in which your
friend resides, walk onto the airplane and settle in for the long ride.
 
When you finally get off the flight at the other end (and discard the
back issues of _Internet Life_ that kept you occupied on the trip), you
stop at the Traveller's Information desk. You present your destination
address to the volunteer attendant and, there being no obvious
alternative, ask for directions. The person at the information desk
consults a list of bus routes -- a routing table -- and determines that
you need to take the Number 17 bus to the end of the line. You climb on
the bus, take out your current issue of _The Atlantic Monthly_ (which you
bought because you didn't want to be seen buying _Wired_ at the airport
newsstand), and read until the bus gets to the end of the line.
 
Once again there seems to be no obvious alternative, so you show your
destination address to a random passerby and ask for directions. She
consults her mental map of the surrounding area (her routing table), and
instructs you to go three blocks up and turn right at the corner with the
house that has the garden gnome shaped like Al Gore. You travel the three
blocks, spot the garden gnome (which really looks more like Diana Rigg to
you, except from one particular angle), turn right, find the house number
from your destination address, and present yourself at the door, proud
(if male) that you've asked for directions twice in one day and even once
from a total stranger.
 
Notice that at each stage of your route, there had to have been some way
to find out how to get to the next stage. If the name of the distant city
hadn't been on the airport directory, or if the people at the information
desk or bus terminus hadn't recognized the address, you wouldn't have
been able to reach your destination. Just having the address wasn't
enough. This is what happens when your address isn't "routed" -- a
process that involves people programming computers, not just computers on
their own. You may send your packet to Sprintnet, because that's where
your default gateway is connected, but unless the destination address you
present to Sprintnet is in _their_ router's routing table, the packet
won't be able to get out of Sprintnet's network.
 
Also note that the process of getting the address from the name didn't
involve routing at all (although in real-life Internet communication, it
usually does).
 
-- Bruce
 
PS. DNS is "Domain Name Service," not Domicile Name Service. (Just in
case!)
 
- B
 
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