Router config on DSL static IP

[Gruntfuttock]

Hi All
Are there any Cisco or DSL guru's who can help.

My ISP has given me a static IP with a subnet mask of 255.255.255.255 which can't be configured in either Windows (to test the bridge from a laptop) or on the router (Cisco 2811). It comes up as an invalid mask.

I intend using a bridge modem (D-Link 300T) with the connection being configured on the router only.

The connection works fine when the modem is set as static using the abv. mask and the laptop connecting with DHCP IP.

Is there a workaround on the router or is the ISP a bit thick in handing out a mask like that? Also, can the gateway address be the same as the IP?

Cheers
Grunt

[ladymuck]

The subnet mask basically is used to identify whether machines are on the same network or not. By having 255.255.255.255 you effectively have a one machine network.

You can use private IP addressing on your internal network using anything in the 192.168.0.1 - 192.168.255.254 range and configure an external router to direct specific data to specific machines. For example, if you have a mail server configured with an IP 192.168.0.10 then you would set the router to allow ports 25 and 110 to route packets to that IP. Email coming in would resolve the domain name to your external IP as given by the ISP and the router then passes the packet on to the appropriate private IP for further pocessing.

[Addanc]

To set-up your static IP address allocated by your ISP (i.e. address seen by external users on the internet), you need to select RFC 1483 Routed or RFC 1483 Bridged mode. This should be possible through the router configuration something like "Internet Connection Type /Encapsulation", at least thats the configurarion options on my ADSL Router a Linksys (=> CISCO systems) box.

[oldgeezer]

May be off the mark here, but as the original post say "It comes up as an invalid mask", could the mask need to be 255.255.255.0 ?

[Toad]

Surely your external IP address is assigned by your ISP's DHCP server (even though it's static), and it's locked into one MAC address only.
255.255.255.255 is the normal subnet mask for an ISP to assign.