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DNS behaviors of a Cisco router are essential subjects for each the CCNA exam and true-world production networks, and you probably did not know there have been so numerous DNS details just before you began studying for the exam! In this tutorial, we'll look at the ip name-server command and its correct usage.

When a command is mistyped on a Cisco router, the default behavior of the router is to try to resolve it by means of DNS. First, the router appears for an IP Host table on the nearby router to carry out this resolution  thats what the translating word in the output is referring to.  If theres no IP Host table or the IP Host table doesnt include an entry for what you typed, the router will send a broadcast in an attempt to resolve this name by way of a remote DNS server. To stop this broadcast, enter the global command no ip domain-lookup. Of course, to use DNS to resolve hostnames, ip domain-lookup would have to be reenabled if its been turned off.

R2#contin

Translating "contin"...domain server (255.255.255.255)

% Unknown command or personal computer name, or unable to find personal computer address

A command is mistyped as contin. The Cisco routers default behavior is to resolve this entry locally by way of an IP Host table, which is not present on the router. A broadcast is then sent out to find a DNS server to execute the name resolution. The DNS lookup attempt need to time out before the configuration can continue.
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R2#conf t

R2(config)#no ip domain-lookup

R2#contin

Translating "contin"

% Unknown command or personal computer name, or unable to uncover laptop address

With no ip domain-lookup configured, the router doesnt try to find a remote DNS server.  It sees there is no neighborhood resolution configured and virtually right away sends a message to the console that the name cant be resolved.

R2#conf t

R2(config)#ip domain-lookup

R2(config)#ip name-server ten.1.1.1

R2#contin

Translating "contin"...domain server (ten.1.1.1)

A DNS server is installed on the network with the IP address 10.1.1.1. DNS lookup is reenabled with the command ip domain-lookup, and the IP address of the DNS server is specified with the ip name-server command.

It is just that simple to tell a Cisco router exactly where the DNS server is!