Network Topology Mapping with CDP and LLDP

Overview

This lab simulates the configuration and operation of Network Time Protocol (NTP) in a multi-router environment to ensure synchronized time across network devices. The lab begins with manually setting the system clock and time zone on each router to establish a consistent baseline. R1 is configured to synchronize with an external NTP server (SRV1), and then act as the time source for R2 and R3. To secure the synchronization process, NTP authentication is implemented using MD5 keys, and routers are configured to trust and authenticate time updates from R1. As a backup, R1 is also set as an NTP master to maintain time continuity in case external synchronization fails. Additional steps include using the ntp update-calendar command and verifying stratum levels and synchronization states with show ntp associations and show ntp status. The lab emphasizes real-world time management practices, secure synchronization, and redundancy planning within Cisco-based networks.

1. Network Topology

For this lab, the topology consists of four routers and one server, with each segment connected using point-to-point links.

The goal for this lab will be to:

• Configure the software clock on R1, R2, and R3 to 12:00:00 Dec 30 2020 (UTC)
• Configure the time zone of R1, R2, and R3 to match my own
• Configure R1 to synchronize to NTP server 1.1.1.1 over the Internet
• Configure R1 as a stratum 8 NTP master
• Configure NTP to update the hardware calendars of R1, R2, and R3

2. Configure Software Clock on R1, R2, and R3

First, I configure the software clock on R1, R2, and R3 by running the following commands on all three routers:

R1> en
R1# clock set 12:00:00 December 30 2020

Now when running the show clock detail command we see the following output:

12:9:21.957 UTC Wed Dec 30 2020
Time source is user configuration

3. Configure Timezone on R1, R2, and R3

Next, I configure the timezone on R1, R2, and R3 to match my own timezone which is PDT which is behind UTC 7 hours.

R1> en
R1# conf t
R1(config)# clock timezone PDT -7

Now when running the show clock detail command we see the following output:

5:4:20.42 PDT Wed Dec 30 2020
Time source is user configuration

4. Configure R1 to synchronize to NTP server

Next, I'm going to configure R1 to synchronize to NTP server 1.1.1.1 over the Internet.

I run the following commands:

R1> en
R1# conf t
R1(config)# ntp server 1.1.1.1

Now when I run show ntp associations we can see that the NTP server is stratum 1:

address         ref clock       st   when     poll    reach  delay          offset            disp
*~1.1.1.1       127.127.1.1     1    20       16      376    4.00           2.00              0.12
 * sys.peer, # selected, + candidate, - outlyer, x falseticker, ~ configured

This means R1 should be stratum 2, which we confirm by running show ntp status:

Clock is synchronized, stratum 2, reference is 1.1.1.1
nominal freq is 250.0000 Hz, actual freq is 249.9990 Hz, precision is 2**24
reference time is E3692E80.00000009 (19:26:56.009 UTC Tue Dec 29 2020)
clock offset is 0.00 msec, root delay is 0.00  msec
root dispersion is 33.13 msec, peer dispersion is 0.12 msec.
loopfilter state is 'CTRL' (Normal Controlled Loop), drift is - 0.000001193 s/s system poll interval is 4, last update was 14 sec ago.

Lastly, we run show clock detail once more to see that NTP has been configured:

2:27:37.551 PDT Wed Dec 30 2020
Time source is NTP

5. Configure R1 as Stratum 8 NTP Master and Synchronize R2 and R3 to R1 with authentication

Next, I'm going to configure R1 as Stratum 8 NTP master and synchronize R2 and R3 to R1 with authentication.

Even though R1 is already stratum 2 because it's connected to the NTP server, I will set it as stratum 8 as well as a backup.

I run the following commands:

R1> en
R1# conf t
R1(config)# ntp master 8
R1(config)# ntp authenticate
R1(config)# ntp authentication-key 1 md5 password
R1(config)# ntp trusted-key 1

Now when running show ntp status on R1 we see it is now stratum 8:

Clock is synchronized, stratum 8, reference is 127.127.1.1
nominal freq is 250.0000 Hz, actual freq is 249.9990 Hz, precision is 2**24
reference time is E369312E.00000198 (19:38:22.408 UTC Tue Dec 29 2020)
clock offset is 0.00 msec, root delay is 0.00  msec
root dispersion is 0.00 msec, peer dispersion is 0.12 msec.
loopfilter state is 'CTRL' (Normal Controlled Loop), drift is - 0.000001193 s/s system poll interval is 4, last update was 2 sec ago.

Now on R2 and R3 I'm going to synchronize and authenticate it with R1:

R2> en
R2# conf t
R2(config)# ntp authenticate
R2(config)# ntp authentication-key 1 md5 password
R2(config)# ntp trusted-key 1
R2(config)# ntp server 192.168.12.1 key 1

Now when running show ntp associations on R2 and R3, we see it connected to R1:

address         ref clock       st   when     poll    reach  delay          offset            disp
 ~192.168.12.1  1.1.1.1         2    422      64      300    0.00           0.00              0.48
 * sys.peer, # selected, + candidate, - outlyer, x falseticker, ~ configured

6. Configure NTP to Update Hardware Calendar of R1, R2, and R3

On R1, R2, and R3 I run the following commands to update the hardware calendar via NTP:

R1> en
R1# conf t
R1(config)# ntp update-calendar

Now, usually, when running show calendar on a Cisco device it will show the settings, but that command does not work in Packet Tracer, so the lab is now complete!