NAT for IPv4

NAT for IPv4

1. NAT Characteristics

   • IPv4 Private Address Space
     • Private Internet Addresses are Defined in RFC 1918
     • NAT provides the translation of private addresses to public addresses
   • What is NAT
     • NAT has a perceived benefit of adding a degree of privacy and security to a network
     • A NAT router typically operates at the border of a stub network
   • NAT Terminology
     • Inside local address Inside global address Outside local address Outside global address

2. Types of NAT

   • Static NAT
     • Static NAT uses a one-to-one mapping of local and global addresses
   • Dynamic NAT
     • Dynamic NAT uses a pool of public addresses and assigns them on a first-come
   • Port Address Translation
     • The ISP assigns one address to the router, yet several members of the household can simultaneously access the internet
   • Next Available Port
     • PAT attempts to preserve the original source port
   • Packets without a Layer 4 Segment
     • Each of these types of protocols is handled differently by PAT

3. NAT Advantages and Disadvantages

   • Advantages of NAT
     • NAT solves our problem of not having enough IPv4 addresses, but it can also create other problems
   • Disadvantages of NAT
     • The fact that hosts on the internet appear to communicate directly with the NAT-enabled device, rather than with the actual host inside the private network

4. Static NAT

   • Static NAT Scenario
     • Static NAT is a one-to-one mapping between an inside address and an outside address
   • Configure Static NAT
     • ip nat inside source static in out
   • Analyze and verify Static NAT
     • show ip nat translations

5. Dynamic NAT

   • Dynamic NAT Scenario
     • The output of the show ip nat translations command displays all static translations
   • Configure Dynamic NAT
     • ip nat pool name in out netmask masl
   • Analyze and verify Dynamic NAT
     • Although static NAT provides a permanent mapping between an inside local address and an inside global address

6. PAT

   • PAT Scenario
     • There are two ways to configure PAT, depending on how the ISP allocates public IPv4 addresses
   • Configure PAT to Use a Single IPv4 Address
     • simply add the keyword overload to the ip nat inside source command
   • Configure PAT to Use an Address Pool
     • To configure PAT to use a single IPv4 address, simply add the keyword overload to the ip nat inside source command
   • Analyze and verifyPAT
     • The process of NAT overload is the same whether a pool of addresses is used, or a single address is used.

7. NAT64

   • NAT for IPv6?
     • IPv6 unique local addresses (ULA) are similar to RFC 1918 private addresses in IPv4 but have a different purpose.
   • NAT64
     • The varieties of NAT for IPv6 are used to transparently provide access between IPv6-only and IPv4-only networks