Re: Static/dynamic NAT and a pool of dynamic/dhcp external addresses?

From: John (jwholmes_at_earthlink.net)
Date: 09/14/03 

Date: Sun, 14 Sep 2003 18:08:02 GMT

On Sun, 14 Sep 2003 10:55:54 +0000, Ralf Strandell wrote:

> Hello
>
> I'm planning to connect a LAN to the Internet. Thus I need to know a few
> things about how NAT (not PAT) and DHCP work together.
>
> Let's assume that I am using static private IP addresses on my LAN and that
> my ISP's DHCP server provides on demand a pool of up to five public dynamic
> IP addresses. Next I would connect my LAN to the Internet using a bridged
> ADSL line.
>
> If I now put a firewall between my LAN and the ADSL modem, then the
> external interface of the firewall gets a dynamic public address from the
> ISP's DHCP server.
>
> I could use PAT to connect the networks, but not all protocolls work with
> it, rigt? At least many multimedia / IP-phone etc. protocols requiring
> multiple return ports would probably fail.
>
> Now the questions...
>
> - Static or dynamic NAT could be used to solve that problem, right?
>
> - But are firewall appliances in general able to bind several dynamic/DHCP
> addresses to the same external interface and then use that pool for static
> or dynamic source NAT?

  What ISP gives you a "pool of up to five public dynamic ip addresses"? I
understand that adsl is generally dynamic but when you ask for multiple
public addresses you generally are buying "business class" and get a pool
of permanent addresses that you can then assign as you see fit. They may
be willing to put the mappings in their dns for you or you may have to
register a domain and run your own dns.

  As for the questions, the first answer is yes and the second is no. If
you have a permanent pool of addresses then the answer becomes yes to both. 

-- 
___________
John Holmes
jwholmes@earthlink.net

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