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Network Address Translation

Chapter Description

Network address translation (NAT) is a function by which IP addresses within a packet are replaced with different IP addresses. This function is most commonly performed by either routers or firewalls. This sample chapter from Cisco Press focuses on NAT within routers.

Troubleshooting Exercises

  1. Identify the mistake in the configuration in Example 4-33.

    Example 4-33 Configuration for Troubleshooting Exercise 1

    ip nat pool EX1 netmask type match-host
    ip nat pool EX1A netmask
    ip nat inside source list 1 pool EX1
    ip nat inside source static
    ip nat outside source list 2 pool EX1A
    access-list 1 permit
    access-list 2 permit
  2. RTR1 in Figure 4-30 connects two internetworks with overlapping addresses.

    Figure 4-30 The Internetwork for Troubleshooting Exercise 2

    NAT is implemented on the router as configured in Example 4-34, but devices cannot communicate across the router. What is wrong?

    Example 4-34 Configuration for Troubleshooting Exercise 2

    interface Ethernet0
     ip address
     ip nat inside
    interface Ethernet1
     ip address
     ip nat outside
    router ospf 1
     redistribute static metric 10 metric-type 1 subnets
     network area 0
    ip nat translation timeout 500
    ip nat pool NET1 netmask
    ip nat pool NET2 netmask
    ip nat inside source list 1 pool NET1
    ip nat outside source list 1 pool NET2
    ip classless
    ip route Ethernet0
    ip route Ethernet1
    access-list 1 permit
  3. Refer to the configurations of Cozumel and Guaymas in Figure 4-21. If the first line of access list 1 in both configurations is removed, what is the result? Can Guaymas and Cozumel still ping each other?