Shulou(Shulou.com)06/01 Report--

NAT failures are often encountered in practical work, which can basically be classified into two categories, namely, misconfiguration and failure to correctly understand the way NAT works. The symptoms of these problems are basically the same, that is, the IP address of the internal local area network is configured with NAT, while the internal local area network is not able to access the external network as expected. If you understand the goal of implementing NAT, and then check the configuration to see if the following error is the cause of the problem, you can generally solve the problem. 1. Whether ACL is set and traffic with or without NAT is blocked. Keep in mind the NAT operations related to ACL when configuring. If ACL is configured for traffic that is not ACL, and the traffic that arrives is actually NAT traffic, this causes the traffic to be discarded. two。 When defining the ACL that requires NAT, the network that needs address translation is omitted. The ACL used to define the network address that needs to be NAT should include all the networks that need to be NAT. The absence of one or more addresses in the list will result in the inability to NAT traffic from those addresses. 3. The overload keyword was omitted in the NAT statement. In order to establish a PAT, the overload keyword must be used at the end of the NAT configuration command. Omitting this keyword will result in the inability to perform PAT, which will eventually result in only a limited number of hosts accessing the public network or the Internet, rather than all the expected hosts. 4. Asymmetric routing causes NAT to fail. NAT occurs when a packet enters an interface that is configured with the ip nat inside command, and when it leaves an interface configured with the ip nat outside command. On a router with many interfaces, you must ensure that all interfaces that require NAT traffic to enter the router are configured with the ip nat inside command, and all interfaces that leave this traffic are configured with the ip nat outside command. Otherwise, traffic cannot be NAT when it passes through an interface that is not configured with the correct NAT command. 5. There are overlapping addresses in the NAT address pool and static NAT entries. It is important to ensure that the ip addresses in the NAT address pool are also not available for static NAT, otherwise it will cause intermittent NAT failures. Intermittent NAT failures can also occur if broadcast addresses are configured into the NAT address pool. 6. Incorrect configuration of inside and outside interfaces will also cause NAT failure. A more useful troubleshooting command is show ip nat statistics, through which you can view various information about NAT. If you want to track the operation of NAT, you can use the debug ip nat command to display each translated packet.

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