NAT in cisco Reg.?

Question

How to configure NAT .... what is NAT pool and overload ..

What is the different between static and dynamic NAT... Plase any one tell me the answer in detail......

Answer 1

Wow, that's a big question!

You seem to write like you know something about networking which is good, you'll need to understand Layer 3 very well to understand NATing.

Basically NAT (Network Address Translation) allows routers and other devices to mask or hid IP addresses from the outside world.  For example, your small home router is doing it now.  Your computer is probably using an address of 192.168.0.100/24 or something similar, but the outside world sees you as 66.12.100.171/20 (not really, but a different address).

Your router is keeping track of all of your address and traffic and it "translates" the source IP address in all of the packets you send to the internet - changes it from your internal IP to the IP of the router.  It then watches to see when traffic comes back and it then translates the destination address in the inbound packets with your internal address.  

So in effect, no one on the internet know your real IP address, only the IP address of your router.

Static vs. Pooled NAT - static means that each host, computer, on the inside is mapped to the same IP on the outside, usually the one external IP of the router/firewall.  Pooled NAT just means that there is a group of external IP's that are used dynamically.  You might not show up as the same IP to people on the internet every time you connect.

NAT Overload is just introducing port address translation (PAT) as well.  If you're not familiar with port, just think of them as like a room number where the IP address is like a building number.  It would be written like this 192.168.1.1:80  

That is representing port 80 on the computer - the port that is usually associated with http (websites).  Well the router that is enabled for NAT overload will change the source IP port number to keep track of who is who on the inside of the network.  This is handy when two comptuers on the inside of the network are connecting to the same host on the outside.  The will appear to have the same source IP, but since the router is changing the port, it will properly redirect the traffic to the right computer on the inside.

Note that in the second paragraph I was writing IP addresses using CIDR, that is I was showing the network mask or the number of bits in the network mask i.e. 192.168.1.1/24 - that 24 bits in the network mask or a Class C address.  (there's a lot to IP, much more than I could explain in this article ;-)

Please note that I've been talking aobut IPv4 and not the new IPv6.  

I know I didn't even touch how you config a cisco router as it's somewhat dependant on the IOS and model, but Cisco's website has some great info on that.

Hope this helped, but I'm sure you'll be able to search for the terms and learn much more than I know about this.

Good luck!