Using Public IPs

[bobcat]

This should be an easy one..but I have yet to find an answer.

-Internet/Serial0--1601---Web, E-mail servers--Firewall--LAN

Right now, the 1601 is NATting the Ip's of the Web and e-mail servers, which is kind of dumb since I have enough public IP addresses to handle all of them. The only reasons I did it with NAT is because of the extra security (which i can replace with some packet filtering) and because I wasn't sure how to do it otherwise.

So, here's where I need help. If I own subnet 123.123.123.16 mask 255.255.255.240, with the router on 123.123.123.17, what do I need to set the IP addresses/mask of Serial0 and Ethernet0 so I can bypass the whole NAT process?

Thanks,
Todd

 

[davidarndt]

Your ISP should have assigned an IP address and subnet mask for you to use on your serial port.

Use
ip address 123.123.123.17 255.255.255.240
on your Ethernet port.

 

[bobcat]

The only one I from the ISP is the 123.123.123.17 255.255.255.240. It is currently attached to my Serial int while the Ethernet is at 10.0.0.1 255.255.255.240. If I try to set the ethernet IP to 123.123.123.17 or something in its subnet it gives me an error saying it overlaps with serial0.

 

[davidarndt]

I see. In that case the only thing you can do is what you are doing now, or split your .240 into two .248's. You would then have six hosts available inside, including your router's Ethernet port. On S0 you would assign

ip address 123.123.123.17 255.255.255.248

and on E0 you would assign

ip address 123.123.123.25 255.255.255.248

Your host machines would have .26 through .30 available.

If you need more host IP's then NAT or a larger address range or a very small (i.e. .252) segment specifically for your router to connect to your ISP's router are the only options I know of.

 

[bobcat]

I figured out a even better way to do it..

on S0:
ip unnumbered eth0

on E0:
ip address 123.123.123.17 255.255.255.240

Works fine so far, and I don't lose any IP's.

 

[wybnormal]

Becareful... you lose the ability to telnet to the router via the serial port.. or ping the ping serial port for troubleshooting. Also, I would recommend setting up a loopback address and then use that for the basis of your unumbered interface.

MikeS
"Diplomacy; the art of saying 'nice doggie' till you can find a rock" Wynn Catlin

 

[davidarndt]

I never thought of using IP unnumbered to the Internet. I definitely concur with wybenormal's advice on the loopback interface.

Isn't it unusual for an ISP to not provide a router serial port address? We've used several different ISP's at our locations and never had that situation.