The role of reverse zone files

[bob prohaska]

Ok some of the dumber fog is starting to lift
Clearly, knowing an address does not tell me how to find a zone
file, forward or reverse. There has to be a reverse chain to go 
with the forward chain for external queries.  

I still don't quite get _how_, given an arbitrary address, the
correct inverse zone file can be found to consult for the hostname.
The key has to be in the chain of in-arpa domains, but I don't
see the connection between my in-arpa zones and my provider's
DNS. Wait a minute, is this what's meant by "reverse delegation"?
Essentially, my ISP saying to the world "these numbers are resolved
by a nameserver at address w.x.y.z?

This is a tougher homework assignment than I bargained for.....
If the logic is not in Hunt's book please warn me and I'll spring
for the other one.

I don't think I'm dealing with a /24 network, which would imply
that I have 8 bits of address space. The netmask given is 
255.255.255.248, which appears to give me three bits or 7 
distinct addesses. Five are said to be "assignable", one is
occupied by the router. Not sure what became of the last one.

 
Thanks for reading, 

bob prohaska