Answers: NTP Client/Server 1

By certskills August 1, 2016 09:10


Configuring a router to have a split NTP personality is not as bad as it sounds. In this lab, you configure NTP client/server mode, plus a couple of NTP clients, and set the timezone. As usual, read the lab and do it for yourself first, and then come back here to check your answers.


Figure 1: NTP Topology

Example 1: R1 Config


Example 2: R2 Config


Example 3: R3 Config



The configuration of NTP is vital on production networking equipment as it ensures that the timestamps that are placed on all logs and events will be referenced to the same time source. Without NTP, any troubleshooting effort that expands past a single device can be complicated to track down. In a typical network, there will be a master source (or sources) that are referenced by all of the devices in the network; each of the network devices will then reference their clocks back to these sources.

For this lab you were tasked with configuring the routers to use NTP. R1 needs to be configured as the main clock in the network while R2 and R3 use NTP as clients, referencing R1. All of the routers also need to be configured to use Eastern Standard Time AND Eastern Daylight Time.

To configure R1 in NTP client/server mode, R1 requires a few extra NTP commands. The first step is to configure it as the master clock source in the network (stratum 3 as suggested in the lab) using the ntp master 3 global command. The second step is to configure R1 to use using the ntp server command. The third step is to configure it to use its Loopback0 as the NTP source; to configure this, use the ntp source Loopback0 command.

All three routers happen to be in the same time zone and all use day light savings time, so all three routers:

  • Set the use of Eastern Standard Time with the clock timeone EST -5 command.
  • Set the router to switch to Eastern Daylight Time with the clock summer-time EDT recurring command.

R2 and R3 act as NTP clients, referencing R1 as the server, so their NTP configuration is identical. The first step is to configure so that they use R1 as their main clock source ( with the ntp server command. (Note that because R1 used the ntp source loopback0 command, R2 and R3 must reference the IP address used on R1’s loopback0 interface.)

CLI Miscellany 1
Extended Named ACLs 1
By certskills August 1, 2016 09:10
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  1. Ruben January 9, 10:10

    Hello Wendell!
    In this lab, I placed both the “timezone” and the “summer-time” commands only on R1!
    I assumed that when R2 and R3 went to R1 to get the time, that time was already adjusted within R1.
    But you placed those commands into all the 3 routers.
    So I assume they are always needed, correct?

    Reply to this comment
    • CCENTSkills January 10, 09:34

      Hi Ruben,
      Yep, those commands are local. For instance, imagine several routers spread over several time zones. You want the time to be synchronized, in that if it’s 8:01:02 in one place, it’s 9:01:02 and 10:01:02 in the other. To make those times 1 and 2 hours different per the time zones, the local settings then set the time zone. Same idea with the daylight savings – some devices may be in locales where they use daylight savings, others not. EG, the next state over from me is Indiana, so in the part of the state where there’s lots of dairy cows, they don’t do savings time, cause it messes with the cows’ schedules too much. 🙂

      Reply to this comment
  2. Felix October 3, 20:03

    Hello Mr Wendell Odom.
    Just a thought, I guess it is necessary the ip name-server A.B.C.D command, so the router resolve into its matching ip address. Page 570 first paragraph of your book. BTW your book is the best.

    Reply to this comment
    • CCENTSkills October 4, 09:55

      Also, good suggestion. I flipped the solution, though: changed the lab problem post to say that name services have already been configured (just to keep with the goal of keeping these labs narrow.) Regardless, your point is spot on. Thanks!

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