How To Configure NTP on Cisco router - GNS3

Network Time Protocol (NTP) is a networking protocol for clock synchronization between computer systems over packet-switched, variable-latency data networks and it works on Application Layer. The protocol uses the User Datagram Protocol (UDP) on port number 123.

I will configure router R1 to use NTP clock synchronization from 2.rs.pool.ntp.org, the source of server from http://www.pool.ntp.org/ which is the largest virtual cluster of time servers.

So let's start.

First check time and date on R1...

R1#show clock

*00:14:33.191 UTC Fri Mar 1 2002

Before we configure R1 to use NTP first of all we need to configure name server and lookup for domain name.

R1(config)#ip domain-lookup

R1(config)#ip name-server 4.2.2.2

Let's test it...

R1#ping www.google.com

Translating "www.google.com"...domain server (4.2.2.2) [OK]

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 173.194.65.104, timeout is 2 seconds:

!!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max = 48/63/72 ms

To configure R1 to use NTP server issue command...

R1(config)#ntp server 2.rs.pool.ntp.org

Translating "2.rs.pool.ntp.org"...domain server (4.2.2.2) [OK]

R1(config)#

As you can see domain server translated name 2.rs.pool.ntp.org to ip address.

R1#show run | include ntp

ntp clock-period 17179864

ntp server 147.91.8.1

Now check time and date on configured router.

R1#show clock          

22:03:23.846 UTC Sat Sep 8 2012

Now we can make R1 to be NTP server for other network devices.

R1(config)#ntp master 1

Later on we can configure another router to use R1 as his NTP server.

R2(config)#ntp server <ip address or host name of R1 in our case>