NTP (Network Time Protocol)

Question 1

How to view time on a Cisco device ?

Answer 1

R1# show clock (default time zone UTC)
R1# show clock detail (see time source)

Question 2

How to manually configure built-in/hardware clock time ?

Answer 2

Built-In:
R1# clock set [00:00:00] [day] [month] [year]

Hardware:
R1# calender set [00:00:00] [day] [month] [year]

Question 3

How to sync the clock and calender ?

Answer 3

R1# clock update-calender (calender to clock)
R1# clock read-calender (clock to calender)

Question 4

How to configure timezone ?

Answer 4

R1# clock timezone [zone] [minutes offset from UTC]

Question 5

How to configure daylight savings time ?

Answer 5

R1# clock summer-time

Question 6

Why do we use NTP ?

Answer 6

It allows auto syncing of time over the network. NTP clients request time from NTP servers (a device can be a client and server at the same time). It allows accuracy between 1-50 milliseconds.

Question 7

What is the distance of an NTP server from the original reference clock called?

Answer 7

Stratum. The lower the Stratum the more accurate the time. Anything above Stratum 15 is considered unreliable. Stratum 0 are Reference Clocks, devices directly connected to Reference Clocks are Primary servers. NTP servers that get their time from other NTP servers are Secondary Servers.

Question 8

What are the 3 NTP modes

Answer 8

Server
Client
Symmetric Active (devices peer with other devices at the same stratum to provide more accurate time)

Devices can be in all 3 modes at the same time. Clients can sync to multiple servers