Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 
New Member

Help setting up 1751 Router / PIX 506E

I need a little help setting up my company's network. I have a Cisco 1751 Router and a PIX 506E Firewall. I only have one Internet IP Address, which I want my internal network to use when going on the Internet. I know I will have to setup the PIX with PAT so my internal users can get out on the Internet. My question is, what should my IP addresses be for the rest of the network, LAN is using 192.168.0.X, I am not sure what IP addresses I should give to PIX’s External/Internal interface and the Router’s NIC connected to PIX’s external interface???????????

Router 1751 ---- PIX 506E ----- Switch -------




Router's IP:

NIC connected to service provider 206.172.X.X

NIC connected to PIX’s external NIC ?

PIX’s IP: External ???

Internal ???

I am new to this, so any help would be greatly appreciated.

Thanks in advance,



Re: Help setting up 1751 Router / PIX 506E

Keep your internal network on the 192.168.0.x network and gateway them all to the PIX inside interface on that network. On the outside IF of the PIX you'll have to use rfc1918 addresses too. I would choose 172.16.x.x or 10.x.x.x for this wire. Then route all traffic to the outside router which will have your PAT address from your SP. Use nat (inside) on the PIX so your inside users get out using their same addresses. When they hit the router, they'll be port translated to their destination and when the traffic returns, it will be translated back to the 192.168.0.x addresses. Oh, make sure to put a route in the outside router pointing your 192.168.0.x addresses back to the outside of the PIX.

CreatePlease to create content