NTP Explained | Network Time Protocol | Cisco CCNA 200-301

Summary

This video from 'Cert Bros' delves into the Network Time Protocol (NTP), emphasizing its critical role in synchronizing network clocks for accurate timekeeping. Inconsistencies in time can lead to issues with log correlation, SSL certificates, and software. The video explains NTP's hierarchical structure, from reference clocks like atomic and GPS devices to primary time servers, and how devices sync to maintain accuracy. It also provides a step-by-step guide on configuring NTP on routers, illustrating the setup with an example using an internet NTP server and showcasing commands to verify synchronization and time accuracy.

Takeaways

• 🕒 NTP, the Network Time Protocol, is essential for synchronizing clocks across a network to ensure accurate timekeeping.
• ⏰ Inconsistent timekeeping can cause issues with log correlation, SSL certificates, and software, even if the discrepancy is just a few minutes.
• 🔢 Every device on a network has an internal clock that tracks both time and date, and it's crucial to keep these clocks accurate.
• 📈 NTP uses a hierarchy system with stratum values ranging from 0 (most accurate) to 15 (least accurate) to identify the accuracy of a clock.
• 🔭 Stratum zero devices, such as atomic clocks or GPS, are the most accurate time sources and do not connect over a network.
• 🌐 Primary time servers, which are directly connected to stratum zero devices, have a stratum value of 1 and are the first layer in the NTP hierarchy.
• 🔄 NTP operates by incrementing the stratum value by 1 at each layer, reflecting the distance from the reference clock and the decreasing accuracy.
• 📶 NTP uses UDP port 123 for communication, making it easy to remember and configure.
• 🌐 For smaller networks, an NTP Internet server can be used as a time source, while larger networks may opt for an internal GPS clock for security.
• 🛠️ NTP configuration involves setting up the time zone, summer time adjustments, DNS server, and specifying the NTP server to sync with.
• 🔍 Two useful NTP show commands are 'show ntp status' and 'show ntp associations', providing information about synchronization status and server details.

Q & A

What is the primary function of NTP?

The primary function of NTP (Network Time Protocol) is to synchronize clocks over a network, ensuring that all devices have accurate and consistent time and date information.

Why is it important to have synchronized time across a network?

Synchronized time is crucial for correlating logs, managing SSL certificates, and avoiding issues that can arise from inconsistencies, such as problems with software or network operations.

What issues can arise if network devices have inconsistent internal clock times?

Inconsistent internal clock times can make it difficult to correlate logs, which can lead to confusion in troubleshooting and could result in looking in the wrong place for issues, especially when dealing with extensive log information.

What is a stratum in the context of NTP?

In NTP, a stratum value identifies the accuracy of a clock, ranging from 0 (most accurate, such as reference clocks like atomic clocks or GPS) to 15 (least accurate), with anything above 15 considered untrustworthy.

How does the stratum hierarchy work in NTP?

The stratum hierarchy in NTP adds a 1 to the stratum value at each layer, with stratum zero clocks being the most accurate and not connecting over a network. As you go down the hierarchy, the stratum values increase, indicating a decrease in time accuracy.

Which UDP port number does NTP use?

NTP uses UDP port number 123 for its operations, making it easy to remember.

What is the role of a reference clock in NTP?

A reference clock, such as an atomic clock, GPS, or radio clock, is a highly accurate timekeeping device that provides the time source for primary time servers in the NTP hierarchy.

How can a network administrator set up NTP on a router?

A network administrator can set up NTP on a router by configuring the time zone, setting up daylight saving time if applicable, assigning a DNS server for domain name resolution, and specifying the NTP server address, which could be an internet NTP server or another internal device.

What are the two useful 'show' commands for checking NTP status and associations?

The two useful 'show' commands are 'show ntp status', which shows if the device has synchronized and the stratum value, and 'show ntp associations', which provides details about the NTP server, including its IP address, reference clock, and stratum value.

How can a router become a stratum 3 device in an NTP setup?

A router becomes a stratum 3 device when it synchronizes its time with an NTP server that is a stratum 2 device, such as an internet NTP server, thus becoming one hop further away from the time source.

What is the significance of stratum values increasing as you go down the NTP hierarchy?

The increasing stratum values indicate that the devices are further away from the primary time source, resulting in less accurate timekeeping. This is important for understanding the reliability of the time information on each device in the network.

Outlines

00:00

🕒 Introduction to NTP and Its Importance

The video introduces the Network Time Protocol (NTP), emphasizing its critical role in synchronizing time across a network. It explains that time inconsistency can lead to issues with log correlation, SSL certificates, and software. The script uses an example of two routers with desynchronized logs to illustrate the potential confusion that can arise without NTP. It then explains the hierarchy of NTP, starting with stratum 0 reference clocks like atomic clocks and GPS, and how stratum values increase as accuracy decreases. The video outlines the setup of an NTP system, including the use of an NTP server and the significance of stratum values in maintaining time accuracy.

05:01

🛠 Configuring NTP on Network Devices

This paragraph delves into the practical setup of NTP on network devices, starting with the configuration of time zones and daylight saving settings to ensure accurate timekeeping. It demonstrates how to set up a router to synchronize with an NTP server, including the use of DNS for domain name resolution and the selection of an NTP server like pool.ntp.org. The script clarifies that NTP does not immediately adjust the clock but gradually aligns it with the server's time. It also introduces two useful commands, 'show ntp status' and 'show ntp associations', which provide information about the synchronization status and the details of the NTP server in use. The paragraph concludes with the configuration of a second router to synchronize with the first, illustrating the cascading effect of NTP synchronization across a network.

Keywords

💡Network Time Protocol (NTP)

NTP is a protocol used for synchronizing the clocks of computers over a network. It is crucial for maintaining accurate timekeeping across devices, which is essential for correlating logs, managing SSL certificates, and ensuring the proper functioning of network services. In the video, NTP is highlighted as the solution to the problem of inconsistent time across network devices, which can lead to issues in log correlation and network management.

💡Stratum

In the context of NTP, stratum refers to a level in the hierarchy of time sources, ranging from 0 (the most accurate, such as atomic clocks) to 15 (least accurate). Stratum values are used to identify the accuracy of a clock, with lower values indicating a more direct connection to a reliable time source. The video explains the concept of stratum and its importance in the NTP hierarchy, using it to illustrate how time accuracy degrades as one moves further from the primary time source.

💡Synchronization

Synchronization in the video refers to the process of aligning the time of network devices with a common reference point, ensuring that all devices have the same time. This is achieved through the use of NTP, which allows devices to adjust their internal clocks to match a more accurate time source. The script uses synchronization to emphasize the importance of consistent timekeeping for network reliability and log correlation.

💡Internal Clock

An internal clock is the timekeeping mechanism within a device that tracks both time and date. The video script mentions that every device on a network has an internal clock, but these clocks can be inconsistent if not synchronized with a more accurate time source, which can lead to problems in correlating logs and other network functions.

💡Log Correlation

Log correlation is the process of comparing and relating log entries from different devices to understand events that occur across a network. The video script uses the example of two routers with unsynced clocks to illustrate how log correlation can be challenging when devices have inconsistent timekeeping, emphasizing the need for NTP to ensure accurate and reliable log analysis.

💡SSL Certificates

SSL (Secure Sockets Layer) certificates are digital certificates that provide secure communications over a network by encrypting data. The video mentions SSL certificates as one of the many things that can be affected by inconsistent timekeeping, as they often have expiration dates that need to be accurately tracked.

💡NTP Server

An NTP server is a device or service that provides accurate time information to other devices on a network. In the video, the script explains how devices synchronize their clocks to an NTP server, which in turn synchronizes with a more accurate time source, such as an atomic clock or GPS. This process ensures that all devices on the network have a consistent and accurate time.

💡UDP Port 123

UDP (User Datagram Protocol) port 123 is the standard port used by NTP for time synchronization messages. The video script mentions this port as a way to remember the protocol's standard configuration, highlighting the simplicity of setting up NTP for network time synchronization.

💡Time Zone

A time zone is a region of the Earth that observes the same standard time. In the video, the script discusses setting the time zone on a router to ensure that the device's clock is adjusted for the correct local time. This is an important step in configuring NTP, as it ensures that the time synchronization is accurate according to the device's geographical location.

💡Summer Time

Summer time, also known as daylight saving time, is the practice of setting the clock ahead of standard time during the longer days of summer, typically by one hour. The video script explains how to configure summer time on a router to account for this seasonal change, which is necessary for maintaining accurate timekeeping in regions that observe daylight saving time.

💡DNS Server

A DNS (Domain Name System) server is a server that translates domain names into IP addresses. In the context of the video, a DNS server is used to resolve the domain name of an NTP server into an IP address, allowing the router to connect to the NTP server for time synchronization. This is an essential step in setting up NTP, as it enables the device to find and communicate with the time source.

Highlights

Introduction to Network Time Protocol (NTP) and its role in synchronizing clocks over a network.

Importance of consistent time for correlating logs, SSL certificates, and software in a network.

Illustration of issues caused by inconsistent time on network devices using router logs as an example.

Explanation of the hierarchy system used by NTP, starting with highly accurate timekeeping devices.

Definition of 'stratum' in NTP and its role in identifying the accuracy of a clock.

Description of stratum values ranging from 0 to 15, with stratum zero being the most accurate.

Clarification that stratum zero clocks do not connect over a network and are directly connected to time servers.

How NTP uses UDP port number 123 for communication.

Real-life setup example using an internet NTP server for smaller networks.

Recommendation to sync an internal device like a router, firewall, or server to an NTP server.

Demonstration of configuring NTP on a router, including setting the time zone and summer time.

Importance of setting a DNS server for translating the NTP server's domain name.

Process of configuring an NTP server on a router and the significance of the stratum value.

Explanation of how NTP gently nudges the time until it's fully synced and tips to speed up the process.

Useful NTP show commands: 'show ntp status' and 'show ntp associations' for checking synchronization and server details.

Configuration of a second router to sync its time with the first router, illustrating the stratum hierarchy.

Final notes on synchronizing the rest of the network devices with the primary NTP server for accurate timekeeping.

Promotion of a full CCNA course related to the video content.

Call to action for viewers to like, comment, and subscribe for channel growth support.

Transcripts

hey what's up guys welcome to cert bros

in this video we're going to be looking

at

[Music]

ntp

ntp stands for network time protocol

it has the very important job of

synchronizing clocks

over a network time is one of those

things that can be

easily overlooked in a network though

having inconsistent time

even just by a few minutes can cause

problems

every device on a network will have an

internal clock

these internal clocks will track both

the time and the date

it's important to keep accurate clocks

otherwise

you may run into issues with correlating

logs

ssl certificates software and the list

goes on

let's take these two routers for example

if something happens to the link

connecting them we may want to look

at the logs our two logs show the line

went down

on the 13th of september at 804

if we then look at our ones logs it

shows the link went down

on the 1st of march at 12 25.

the link went down at the same time but

because the internal clocks are not

synced

it would be very difficult to correlate

these logs

now this is an extreme example but when

dealing with a lot of log information

even a few seconds can mean you're

looking in completely the wrong place

the problem is when our networks grow

keeping on top of the time and date for

every device

becomes nearly impossible this is where

ntp comes in

all of the devices will sync their

clocks to an ntp server which will have

an accurate time

so now we know the importance of ntp and

what it does

let's look at how it works ntp uses a

hierarchy system

at the very top we have the big boys the

mack daddies

these are highly accurate timekeeping

devices such as

atomic clocks gps or radio clocks

they are known as reference clocks they

have a stratum

of zero meaning they are the most

accurate

what does strata mean ntp uses stratum

values to identify the accuracy of a

clock

stratum values range between 0 to 15

with 0 being the most accurate and 15

being the least

anything above 15 means the accuracy of

the clock is not

trustworthy stratum zero clocks do not

connect over a network

they are directly connected to time

servers

they then sync their time and date to

the reference clock

these are known as primary time servers

the way the ntp strata model works is by

adding a 1

to the stratum value at each layer so

these primary time servers have a

stratum value of 1.

as we go further down the stratum

hierarchy the stratum values increase

this is because the reference clock is

further and further

away meaning the time is less accurate

ntp uses udp port number one

two three so that's nice and easy to

remember

let's look at how a real-life setup

could look using ntp

first we need a time source for smaller

networks

that source is likely going to be an ntp

internet server

for larger more security conscious

environments you may have your own

internal gps clock

i'll use an internet ntp server for this

example

there are several ntp servers available

you just need to do

a quick google search pool.ntp.org

is a popular one when connecting to an

internet ntp server

most of the time it will be a stratum 1

2 or 3 server

you should then sync an internal device

to that ntp server

this could be a router firewall or

server the choice is up to you

i'll be using this router once our

router is synced

we can then use it to provide the time

for the rest of the network

this makes our router a stratum 3 device

this is because

our internet ntp server in this example

is a stratum 2.

if you have a more complex network with

multiple routers

firewalls and vlans you may set up more

internal ntp

servers let's try this for real

i'm going to show you a basic ntp

configuration

here is router 1. it's already got an ip

address and it's connected to the

internet

the first thing we need to do is set up

the time zone and summer time

not doing this can make our clock

incorrect even with an ntp server

so first let's set the time zone

in config mode type clock

time zone and because i'm in the uk

we'll use gmt which is simply a word

and 0 0 because it syncs up with the utc

time

your time zone might be different

next let's change the summer time over

here we have something called

british summer time this is where our

clocks go forward and back

during the summer to set this up we need

to type

clock summer time

bst which again is just a word

and to make sure this reoccurs we're

going to type recurring

last sunday of march

at 1am so that's when our clocks go

forwards

and last sunday of october

at 2 a.m which is when our clocks go

back

okay now that's set we need to give our

router a dns server

that's because we need to translate our

ntp server's domain name

to set this up we need to type ip

name server and i'm going to use

google's dns server which is 8.8.8.8

next we need to tell our router where to

sync the time from

so i'll type ntp server

and now the name of the ntp server which

is pool.ntp.org

now this is a domain name that's going

to translate to my nearest ntp server

so that's why we needed to set the dns

an important note here

is that ntp doesn't sync the clock

straight away

the way the algorithm works is by gently

nudging the time

until it's fully synced so this can take

a few minutes

you can speed this up by manually

setting the clock as close to the

accurate time as possible

then ntp doesn't have as much work to

sync up

there are two useful show commands for

ntp

let's exit out of here to privilege exec

mode

the first command is show ntp status

this will show you if the device has

synchronized

the stratum value of the device and the

ip address of the ntp

server used for reference

if we type show ntp associations

this will show us the details of the ntp

server we're using

it shows us the ip address of the ntp

server

and the ip address of its reference

clock

it also shows us the stratum value of

the ntp server

and of course we can always check the

time is correct by running the

show clock command

so now this router is synced with our

ntp server

let's open router

we need to configure this router to sync

its time with router 1.

again all of the interfaces are already

configured

so i'll open global config by typing

configure terminal

and quickly set the time zone clock time

zone

the word gmt 0 0

and then the summer time by typing clock

summer time

the word bst recurring last sunday of

march at 1am

last sunday of october at 2 am

now let's set the ntp server ntp server

and i'll type the ip address of router 1

which is 192.168.0.254

just as before we can exit out of here

and use the show command

show ntp status

and as we can see it has now

synchronized with router 1.

we can also see that this router has a

stratum value of

4 which is 1 higher than router 1.

this is because we are now one hop

further away from the source

if we type show ntp associations

we can see router's one ip address its

reference clock

and its stratum value so there we have

it a nice and

simple ntp configuration you could then

configure the rest of your devices to

synchronize their time with router 1

and they will all be synchronized and

accurate this video is part of our full

ccna course which can be found

in the description so please feel free

to go and check that out

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other than that thank you for watching