NAT Overview for CCNA

As I prepare for the CCNA, I collected all my various notes and have tried to put the highlights here for quick reference as my test date approaches.

3 Types of NAT:

  • Dynamic NAT – might be used between networks with overlapping address schemes.  This is the least common form of NAT.
  • NAT Overload / Port Address Translation (PAT)
  • Static NAT – straight “one-to-one” Private to Public IP address translation.

Configure NAT Overload with the CLI (3 steps)

  • Label the interfaces
  • Identify the internal IP addresses to be translated (with ACL)
  • Enable NAT overload

LABEL INTERFACES

router1#config t
router1(config)#int gi0/0
router1(config-if)#ip nat inside
router1(config-if)#
router1(config-if)#int gi0/1
router1(config-if)#ip nat outside
router1(config-if)#
router1(config-if)#exit
router1(config)# 

Identify Internal addresses to be translated (with ACL)

router1#config t
router1(config)#ip access-list standard NAT_ADDRESSES
router1(config-std-nacl)#permit 192.168.0.0 0.0.255.255
router1(config-std-nacl)#
router1(config-std-nacl)#exit
router1(config)#

*Make a note that the name of the ACL is totally up to you, I just used this for ease of identification.

Enable NAT Overload

router1#config t
router1(config)#ip nat inside source list NAT_ADDRESSES interface gi0/1 overload      
router1(config)#
router1(config)#exit

That is it for configuring NAT Overload, just 3 easy steps (as long as you can remember the steps).

Static NAT configuration

The next common form of NAT, is the straight forward Static NAT.  This is where we will simple link an inside IP address with a public IP address.  In this next example I will map the inside address of 192.168.10.50 to the outside address of 68.110.171.99

router1#config t
router1(config)#ip nat inside source static 192.168.10.50 68.110.171.99
router1(config)#exit
router1#

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