Cisco CCNA Certification Exam Tutorial: DNS name and IP-Server Command

DNS behavior of a Cisco router are important issues for both the CCNA exam and real production networks worldwide, and you probably did not know there were so many DNS details before you began studying for Review! In this tutorial we'll look at the ip name-server command and its proper use.

When a command is mistyped on a Cisco router, the default router is attempting to resolve the DNS. First, the router looks for a table of IP host on the local router to perform this resolution - that's what the "translating" word in the output refers. If there is no table d'hote or IP of the IP host table contains no entry for what is typed, the router sends a broadcast to resolve this name through a DNS server remote. To avoid this broadcast, enter the global command no ip domain-lookup. Of course, to use DNS to resolve hostnames, ip domain-lookup will be reactivated if it has been disabled.

Contin R2 #

Translate "continues" ... domain server (255.255.255.255)

% Unknown command or computer name, or unable to find the address of the computer

A command is misspelled as "Contin. Default behavior of Cisco router is to resolve this entry locally via an IP host table, which is not present on the router. A program is then sent to find a server to perform DNS name resolution. The DNS lookup attempt must time out before the configuration can continue.

R2 # conf t

R2 (config) # no ip domain-lookup

Contin R2 #

Translate "continues"

% Unknown command or computer name, or unable to find the address of the computer

With "no ip domain-lookup" configured, the router does not try to find a remote DNS server. She sees no local resolution configured and almost immediately sends a message to the console that the name can not be resolved.

R2 # conf t

R2 (config) # ip domain-lookup

R2 (config) # ip name-server 10.1.1.1

Contin R2 #

Translate "continues" ... domain server (10.1.1.1)

A DNS server is installed on the network with IP address 10.1.1.1. DNS Lookup is reactivated with the field of IP-Lookup command and the IP address of the DNS server is specified with the ip name-server command.
It's just that easy to tell a Cisco router exactly where the DNS server is!

Chris Bryant, CCIE # 12,933, is the owner of The Bryant Advantage, home of more than 100 tutorials free certification exam, including tests for Cisco CCNA certification prep items. Exclusive Cisco CCNA study guide her and Cisco CCNA training is also available!

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