IP Addressing Scheme & Configuration HELP!


I have obtained a static IP address from my ISP.

I would like to use a static IP addressing scheme for my LAN and would like to base it on the net format.

I have 2 PC's, a Firewall, and an ADSL Modem.

In particular, I would appreciate advice on the following:

>> Starting with the PC being addressed as IP, what addresses / subnet masks / default gateways do I assign to the PC, Firewall and Modem?

>> I assume that DHCP should not be enabled on both the Modem and Firewall?

>> Can the Management IP addresses of the Firewall and Modem be part of the LAN addressing scheme?

I need some HELP to get my Firewalled-LAN up and running and to have internet access.

Advice is very much appreciated.

Many thanks.
6 answers Last reply
More about addressing scheme configuration help
  1. First, I'm going to make an assumption: What you call a 'firewall' is really a 4-port broadband router, correct?

    Out of the box, those routers are set to use (usually) as their IP addy, and DHCP is enabled. That setup should work fine in 99.999% of cases. If you want to change it, you can change it to anything you want.

    Only have 1 device with DHCP enabled on any individual network segment, so if 2 have it enabled, disable one of them.

    I never use 0 as the last octet, but I suppose you could.

    If you want the addy's to be 10.0.0.x and have it manually configured, then pick a number for each device - i.e., router =, PC1 =, PC2 =, etc. Make sure every device stays in the 10.0.0.x 'subnet', and make your subnet mask Default gateway will be the IP addy of the router. Modem shouldn't have a specific addy, because most ADSL modems are really just bridges and htey don't care.


    <font color=blue>Outside of a dog, a book is man's best friend. Inside the dog its too dark to read.
    -- Groucho Marx</font color=blue>
  2. By default, your router will be a 192.168.x.x number. Change that to something like (routers generally are .1).
    Subnet mask can technically be whatever in this situation.. since you want to use the standard corporation IP address range: Class A, subnet will be

    So, you can do with subnet of - or - you're not subnetting or supernetting, so it really doesn't matter. Just stick to for standard troubleshooting.

    Assign your computers whatever,

    In most cases, you'd setup DHCP to dish this stuff out and be done with it, but if you don't want to use DHCP, disable it.

    Default gateway will be (router's IP address)



    The only IP that will be different is the external (Public) IP address of your Router.
  3. Thanks very much for the replies.

    My Firewall is a "Watchguard Firebox SOHO 6" model with 4 trusted LAN sockets and a WAN socket.

    My Modem is a "D-Link Ethernet ADSL 300T" model.

    Does the fact that I have a separate firewall device change your answers in any way?


  4. Hi.

    After much puzzlement, trying to configure my LAN - without success - I think my problem is to be resolved soon.

    I am with an ISP that is using PPPoA to give me a static IP.

    The SOHO firewall doesn't like PPPoA apparently.

    So, at last I'm moving forward!

    Thanks for your interest.


  5. If your SOHO Router doesn't support PPPoA, you can try using the provided software to establish the connection through the router. PPPoA has been getting replaced by PPPoE for a while now though.
Ask a new question

Read More

Static IP Firewalls Modem Internet Service Providers Networking