NAT/PAT

1.   NAT stands for Network Address translation.

2.   PAT stands for Port Address translation.

3.   NAT/PAT came to use because private IP addresses are not allowed on internet. So we have to somehow convert private IP addresses into public IP addresses and vice versa.

4.   NAT & PAT is used to convert private IP address into public IP address and vice-versa.

5.   We configure NAT/PAT on our edge router from where traffic will enter and exit our network.

6.   Private IP range:

·     Class A (10.0.0.0 – 10.255.255.255)

·     Class B (172.16.0.0. – 172.31.255.255)

·     Class C (192.168.0.0. – 192.168.255.255)

7.   NAT is of two types:

·     Static NAT (one to one mapping)

·     Dynamic NAT (many to many mapping)

8.   In Static NAT, we have to convert each private IP address of our network into public IP address manually.

9.   In Dynamic NAT, we will create an Access list and will place private IP address in that list. Then we will have a NAT pool in which we will place our public IP address range. One private IP from access list will be mapped with a public IP address from NAT pool. This public address pool is temporary in nature.

10.                 Static NAT configuration:

·     On edge router, give following commands:

Router(config)#interface fastEthernet 0/0(inside interface)

Router(config)#ip nat inside

Router(config)#interface fastEthernet 0/1(outside interface)

Router(config)#ip nat outside

Router(config)#ip nat inside source static (inside local IP) (inside global IP)

11.                 Dynamic NAT configuration:

·     On edge router, give following commands:

Router(config)#interface fastEthernet 0/0(inside interface)

Router(config)#ip nat inside

Router(config)#interface fastEthernet 0/1(outside interface)

Router(config)#ip nat outside

·     Create an access list and permit your private network.

Router(config)#access-list (number) permit (private IP range) (wildcard bit)

·     Create a NAT pool.

Router(config)#ip nat pool (name) (starting public IP) (end public IP) netmask (value)

·     Then give following commands:

Router(config)#ip nat pool inside source list (access-list no) pool (NAT pool name)

12.                 PAT (many to one mapping)configuration:

·     On edge router, give following commands:

Router(config)#interface fastEthernet 0/0(inside interface)

Router(config)#ip nat inside

Router(config)#interface fastEthernet 0/1(outside interface)

Router(config)#ip nat outside

·     Now do following configuration:

Router(config)#ip nat pool inside source list (access-list no) interface (interface on which your public IP is configured) overload