The configuration above defines the FastEthernet interface as NAT inside and the loopback interface as NAT outside.
R2(config)# ip nat inside source list 100 interface loopback0 overload R2(config)# access-list 100 permit icmp any any port-unreachable R2(config)# access-list 100 permit icmp any any time-exceeded To achieve this we’ll configure NAT on R2: The task requires this output to show the 2.2.2.2 address from the loopback interface. R2(config-if)# ip address 2.2.2.2 255.255.255.0īefore we dive into the NAT configuration let’s do a trace and look at the output:Īs expected R2 responds with the IP address on its FastEthernet interface. Let’s configure these IP addresses first: R2 has a loopback 0 interface with IP address 2.2.2.0 /24. There are only two routers that are directly connected to each other. First of all, this is the topology that we will use:
In this tutorial I’ll show you this is done. To make this work we have to configure the NAT on a stick feature. This sounds easy enough but there’s no such thing as a “traceroute source loopback 0″ command or anything alike. “Make sure that whenever R2 responds to a traceroute it replies with the IP address on the loopback 0 interface” NAT (Network Address Translation) is most commonly used to let users on our LAN access the Internet using a single public IP address but it can be used for some more interesting scenarios.Recently I encountered an interesting CCIE R&S task that had the following requirement:
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