NTPv4 is an extension of NTPv3 that supports IPv4 and IPv6. It is backward compatible with NTPv3, offers some new features, and time synchronization is faster and more precise.

Security has improved, NTPv4 supports public key cryptography and standard X509 certificates.

When using NTP for IPv4, broadcast is a popular option as it allows you to send NTP packets in the broadcast domain to everyone. We can’t do this with IPv6, but NTPv4 does support site-local multicast.

DNS support is also improved. With NTPv3, if you configure a hostname to sync with, your device does a lookup for the hostname and stores the IP address in the configuration, the hostname is then lost. With NTPv4, the hostname is stored in the configuration.

In this lesson, I’ll show you how to configure NTPv4 with a unicast and multicast client.


This is the topology we’ll use:

Ntpv4 Lab Topology

Configuration-wise, NTPv4 is pretty much the same thing.

To help speed things up, let’s set the same time and date on all routers before we configure NTP:

R1, R2 & R3
#clock set 10:37:00 2 July 2018

I will configure R1 as an NTP master so that I don’t need an external server:

R1(config)#ntp master 1


Let’s configure our clients. R2 will be an NTP unicast client and for R3 we will use multicast.


We can configure the IPv6 address of R1 but instead, we’ll use a hostname to test if R2 stores the hostname in its configuration. I’ll create a manual host record for this:

R2(config)#ipv6 host R1 2001:DB8:0:12::1

Now we configure R1 as the NTP server. The version 4 parameter sets the correct version:

R2(config)#ntp server R1 version 4


To make multicast work, we need to configure R1 to send NTP multicast packet and R3 to receive them.

This is the multicast address we will use:


  • FF05 is the multicast address for the site-local scope.
  • ::101 is the address that IANA has assigned to NTP for IPv6.

Let’s configure R1 to send NTP multicast packets with this address:

We're Sorry, Full Content Access is for Members Only...

If you like to keep on reading, Become a Member Now! Here is why:

  • Learn any CCNA, CCNP and CCIE R&S Topic. Explained As Simple As Possible.
  • Try for Just $1. The Best Dollar You've Ever Spent on Your Cisco Career!
  • Full Access to our 660 Lessons. More Lessons Added Every Week!
  • Content created by Rene Molenaar (CCIE #41726)

503 Sign Ups in the last 30 days

100% Satisfaction Guaranteed!
You may cancel your monthly membership at any time.
No Questions Asked!

Tags: ,

Forum Replies

  1. Hello Guy!

    The first complete specification of NTP, that is, Version 1, appeared in 1988 (RFC 1059) which provided simple symmetric and client server mode operation.

    Version 2 appeared in 1989 (RFC 1119) and added symmetric key authentication using DES-CBC.

    Version 3, which is the version that is most used today was first described in 1992 (RFC 1305) and has been systematically improved over the years. It introduced formal correctness principles, revised algorithms and broadcast mode . This is the default version that is available in most Cisco devices using

    ... Continue reading in our forum

  2. Hello Laz,
    A few questions.

    1. Let’s say I have a router that is configured to receive the ntp information from a ntp server located in the internet. I have also configured the time locally by using clock set command. Which time will have more preference? In another words, which time the router will use?
    2. What is the command to change time-zone in a router?
    3. Let’s say a router is configured to sync its time from a ntp server and the ntp server is feeding UTC time to the router. However, I like the router to show EST time in the clock or let’s say in syslog message
    ... Continue reading in our forum

  3. Hello AZM

    **Question 1**
    When NTP is configured on a device, there is what is called a poll interval. This interval is dynamic and as client and server become better synced, and there aren’t any dropped packets, this interval increases to a maximum of 1024 seconds. If you change the time using the clock set command, the time you set will become the new time. However, when the poll interval is exhausted, the device will re-sync with the NTP server. So any changes you make manually will be over-ridden at the next poll interval.

    **Question 2**
    To change the ti

    ... Continue reading in our forum

  4. Hi Sreenath,

    NTP and PTP have some similarities. NTP is the most common protocol to sync clocks on your network, that’s what you will mostly see on networks nowadays. We use it to sync the clock on network devices but also computers/servers etc. NTP uses software timestamping and supports millisecond synchronization.

    PTP is similar to NTP but uses hardware timestamping and offers nanosecond or picosecond-level synchronization.

    For 99% of the devices, NTP is good enough but if you have devices where millisecond-level synchronization is not good enough, PTP is an

    ... Continue reading in our forum

  5. Hello Kevin,

    NTP authentication can be confusing. With your configuration, no authentication occurs because the client isn’t configured for authentication. I did a quick lab with your configuration.

    The server will send “regular” NTP packets without an MD5 hash. Once you change the ntp server command on the client, it works.




    Client(config)#ntp server key 1


    Once the client wants to use authentication, the server responds with the same MD5

    ... Continue reading in our forum

54 more replies! Ask a question or join the discussion by visiting our Community Forum