NAT (or) Network Address Translation

NAT (Network Address Translation) can be configure in ROUTER or ASA or any other NAT cabpable devices. {example, Firewall, Load Balancer, Layer-3 switch, ...}

NAT, normally applies INSIDE to OUTSIDE (example: to internet)
Sometimes, applies INSIDE to INSIDE (example: internal web application)

most commonly used NAT are:

• 1 to 1 Static NAT (example: public website, www.something.com)
• 1 to Many Dynamic NAT (or) PAT (example: enterprise user network)

the other NAT (for Cisco ASA) are:

• NAT ZERO (or) NAT excemption (example: site to site VPN)
• Static Identity NAT
• Dynamic Identity NAT
• Static Policy Identity NAT

for more detail click HERE

Below is an example for 1 to many NAT (PAT) Configuration on Cisco ROUTER,

Step 1
! define the NAT interface

interface e0/0
ip address 192.168.1.1 255.255.255.252
ip nat outside
no shut

interface e0/1
ip address 10.1.1.1 255.255.255.0
ip nat inside
no shut

Step 2
!define the Access-list

access-list 1 permit 10.1.1.1 0.0.0.255
access-list 1 deny any

Step 3
!define the NAT

ip nat inside source list 1 interface e0/0 overload

Step 4
!verification

R1#show ip nat translations 
Pro Inside global      Inside local       Outside local      Outside global

icmp 192.168.1.1:3     10.1.1.2:3         192.168.1.2:3      192.168.1.2:3

R1#debug ip nat
NAT*: s=10.1.1.2->192.168.1.1, d=192.168.1.2 [25]

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Foot Notes:

Before Natting, ensure TCP reachability to NAT addresses.