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T1 Accessing Public IP Address's

Ok, just got a Integrated T1 line (Voice and Data) installed with an Adtran 3200 Router. The Telco company configured the router for nat and everything is working great. With the service I have 5 public ip addresses. I would now like to use one of the public IP addresses included in my block. Currently, when I check to see what public IP address all the nat clients are running out of it is the one the telco company calls the Customer Serial IP Address. Here is the setup

WAN Default Gateway - *.151.101.57
Customer Serial IP - *151.101.58
Subnet Mask - 255.255.255.252

Public Lan Network - *153.125.200
Usable IP's - *153.125.201-206
Subnet Mask - 255.255.255.248

NAT Clients for Internet Access - Default Gateway 192.168.1.1

How can I access one of the public IP addresses? I plan on puting a router behind it and running nat for a separate network. Should I disable NAT on the T1 Router?

Site Note Questions:
Why did the telco company choose to run nat behind the customer serial ip address and not a public lan address?
What is the purpose of the Serial IP addresses, why can't you interface the Default Public Lan Gateway directly to the Telcos Router and eliminate the Serial IP Addresses (If this doesn't make any sense just say so)?

Also, We have a PBX running with this configuration and I don't want to disrupt its service:

Avaya IPOffice 403 PBX - 192.168.42.2
Computer To Configure PBX - 192.168.42.1

Thanks in advance.

ASKER CERTIFIED SOLUTION

The--Captain

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HTGPRG

ASKER

Thanks for the Response Jon...

ISP Supplied Information:
*******************************
WAN Default Gateway - *.151.101.57
Customer Serial IP - *151.101.58
Subnet Mask - 255.255.255.252

Public Lan Network - *153.125.200
Usable IP's - *153.125.201-206
Subnet Mask - 255.255.255.248
*******************************

Ok, does this sound right to do?

I'm going to Disable Nat on the T1 Router and currently the ISP doesn't have DHCP enabled. After disabling NAT, I should assign the Public Lan Network Address (*.153.125.200 /29) to the Adtran internal ethernet interface. Now my router will be routing all the public addresses properly therefore I can go ahead and grab any of the usable ones [201-206] and do as I please. To clear things up, the ISP did not tell me I had 5 usable addresses, I assumed that from the /29 subnetting since you loose two automagically and 1 for the gateway. But you are correct in stating that they are claiming I have 6 available. Do you think that based on the configuration they told me that the Public Lan Network Address is the Default Gateway for the usable IP's or is that one of the addresses you loose during subnetting and maybe one of the IP addresses from the public ones they gave me is the Default Gateway for those addresses, either 201 or 206?

Also, you stated...
"1. Assign one of your public IPs (*.153.125.201-206) to the Adtran internal ethernet interface (assuming it does not already have an assigned public IP address) "

If NAT is enabled on the Router wouldn't the Interal Ethernet Interface be the NAT Default Gateway Address which is 192.168.1.1 for my particular setup?

Thanks for your patience and help.

HTGPRG

ASKER

Your Answer was perfect, forget the last comments.

Thanks.