NAT FOR IPV4

NAT FOR IPV4

1. NAT OPERATION

   • NAT CHARACTERISTICS
     • IPv4 Private Address Space
       • there are not enough public IPv4 addresses to assign a unique address to each device connected to the Internet. Networks are commonly implemented using private IPv4 addresses, as defined in RFC 1918.
     • 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 Terminology
       • NAT includes four types of addresses: Inside local address, Inside global address, Outside local address, Outside global address
     • How NAT Works
   • TYPES OF NAT
     • Static NAT
     • Dynamic NAT
       • Dynamic NAT uses a pool of public addresses and assigns them on a first-come, first-served basis. When an inside device requests access to an outside network, dynamic NAT assigns an available public IPv4 address from the pool.
     • Port Address Translation (PAT)
     • Next Available Port
       • In the previous example, the client port numbers, 1331 and 1555, did not change at the NAT-enabled router. This is not a very likely scenario, because there is a good chance that these port numbers may have already been attached to other active sessions.
     • Comparing NAT and PAT
   • NAT ADVANTAGES
     • Advantages of NAT
     • Disadvantages of NAT

2. CONFIGURE NAT

   • CONFIGURING STATIC NAT
     • Configure Static NAT
     • Analyzing Static NAT
     • Verifying Static NAT
       • A useful command to verify NAT operation is show ip nat translations. This command shows active NAT translations. Static translations, unlike dynamic translations, are always in the NAT table.
   • CONFIGURE DYNAMIC NAT
     • Dynamic NAT Operation
       • While static NAT provides a permanent mapping between an inside local address and an inside global address, dynamic NAT allows the automatic mapping of inside local addresses to inside global addresses. These inside global addresses are typically public IPv4 addresses.
     • Configuring Dynamic NAT
     • Analyzing Dynamic NAT
     • Verifying Dynamic NAT
       • he output of the show ip nat translations command shown in Figure 1 displays the details of the two previous NAT assignments. The command displays all static translations that have been configured and any dynamic translations that have been created by traffic.
   • CONFIGURE PAT
     • Configuring PAT: Address Pool
     • Configuring PAT: Single Address
     • Analyzing PAT
       • The process of NAT overload is the same whether a pool of addresses is used or a single address is used. Continuing with the previous PAT example, using a single public IPv4 address, PC1 wants to communicate with the web server, Svr1.
     • Verifying PAT
       • Router R2 has been configured to provide PAT to the 192.168.0.0/16 clients. When the internal hosts exit router R2 to the Internet, they are translated to an IPv4 address from the PAT pool with a unique source port number.
   • CONFIGURE PORT FORDWARING
     • Port Forwarding
       • Port forwarding is the act of forwarding traffic addressed to a specific network port from one network node to another. This technique allows an external user to reach a port on a private IPv4 address (inside a LAN) from the outside, through a NAT-enabled router.
     • Wireless Router Example
     • Configuring Port Forwarding with IOS
   • NAT IPV6
     • NAT for IPv6?
       • Since the early 1990s, the concern about the depletion of IPv4 address space has been a priority of the IETF. The combination of RFC 1918 private IPv4 addresses and NAT has been instrumental in slowing this depletion. NAT has significant disadvantages, and in January of 2011, IANA allocated the last of its IPv4 addresses to RIRs.
     • IPv6 Unique Local Addresses
       • IPv6 unique local addresses (ULA) are similar to RFC 1918 private addresses in IPv4, but there are significant differences as well. The intent of ULA is to provide IPv6 address space for communications within a local site; it is not meant to provide additional IPv6 address space, nor is it meant to provide a level of security.
     • NAT for IPv6
       • NAT for IPv6 is used in a much different context than NAT for IPv4. The varieties of NAT for IPv6 are used to transparently provide access between IPv6-only and IPv4-only networks. It is not used as a form of private IPv6 to global IPv6 translation.

3. TROUBLESHOOT NAT

   • NAT TROUBLESHOOTING
     • The show ip nat Commands
     • The debug ip nat Command
       • Use the debug ip nat command to verify the operation of the NAT feature by displaying information about every packet that is translated by the router. The debug ip nat detailed command generates a description of each packet considered for translation.
     • NAT Troubleshooting Scenario

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