[CLUE-Tech] cisco 675 config for static IP's?

[Dave Anselmi]

Dave Price wrote:

> Gang,
>
> I have a cisco 675 DSL router and a block of 6 usable IP addresses from
> Qwest.

Take a look at this thread:

http://clue.denver.co.us/pipermail/clue-tech/2001-December/002281.html

it covers most of what I know on the subject.  Especially look at the
nat.pdf link in one of the posts.  I'll skip your specific questions because
that should give you a better idea what you want.

Fundamentally, the 675 can handle several networks and keep all the
"routing" straight.  It does route, but since it only has 2 interfaces all
the networks share them.

You can use the dynamic IP NAT'ed to a private internal network in addition
to the public IPs you have (you could probably NAT them too, but that would
be silly).

Anything you can do with the 675, you can do with your firewall box, and
more since you can put more than 2 interfaces in it.  But even with 2 you
can duplicate what the 675 does (primarily that means having one interface
on multiple networks).

Finally, Qwest is giving you at /29 address block.  That means you have 8
IPs available (32 address bits - 29 bits for the network part leaves 3 bits
for hosts).  But only 5 are usable for hosts (I'm not sure where you got
6).  The reason is that the adress that ends with three 0 bits is the
network address and the one ending in three 1 bits is the broadcast
address.  And you need one for the gateway - the 675.  That's a limitation
of CIDR (classless internet domain routing).  I can conceive ways to avoid
assigning a gateway address, but I've never seen it done that way and don't
have anywhere to test it out.

HTH, ask back if not.

Dave