NAT for IPv4

NAT for IPv4

1. What is NAT?

   • NAT has many uses, but its primary use is to conserve public IPv4 addresses. It does this by allowing networks to use private IPv4 addresses internally and providing translation to a public address only when needed.
   • NAT has an added benefit of adding a degree of privacy and security to a network, because it hides internal IPv4 addresses from outside networks.

2. NAT Terminology

   • Inside local address
   • Inside global address
   • Outside local address
   • Outside global address

3. NAT Terminology (Cont.)

4. Static NAT

   • Static address translation (static NAT)
   • Dynamic address translation (dynamic NAT)
   • Port Address Translation (PAT)

5. Dynamic NAT

   • Dynamic NAT uses a pool of public addresses and assigns them on a first-come, first-served basis.

6. Comparing NAT and PAT

   • NAT forwards incoming packets to their inside destination by referring to the incoming source IPv4 address given by the host on the public network.
   • With PAT, there is generally only one or a very few publicly exposed IPv4 addresses. Incoming packets from the public network are routed to their destinations on the private network by referring to a table in the NAT router.

7. Advantages of NAT

   • NAT conserves the legally registered addressing scheme by allowing the privatization of intranets.
   • NAT increases the flexibility of connections to the public network.
   • NAT provides consistency for internal network addressing schemes.
   • NAT hides user IPv4 addresses. Using RFC 1918 IPv4 addresses, NAT provides the side effect of hiding users and other devices’ IPv4 addresses.

8. Disadvantages of NAT

   • Performance is degraded
   • End-to-end functionality is degraded
   • End-to-end IP traceability is lost
   • Tunneling becomes more complicated
   • Initiating TCP connections can be disrupted

9. Configuring PAT: Address Pool

10. Configuring PAT: Single Address

11. Port Forwarding

    • Port forwarding is the act of forwarding traffic addressed to a specific network port from one network node to another.

12. Configuring Port Forwarding with IOS

13. NAT for IPv6?

    • Since the early 1990s, the concern about the depletion of IPv4 address space has been a priority of the IETF.

14. The show ip nat Commands

    • Using the range of addresses 209.165.200.226 to 209.165.200.240.

15. The debug ip nat Command

    • The debug ip nat detailed command generates a description of each packet considered for translation.

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