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So one of the strategies of getting network time protocols said that correctly

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is to have a good game plan.

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So here's what I propose we do for our initial game plan.

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Let's configure R1 and R2 as top level NTP servers.

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Now one way of doing that would be to have them connected to an atomic clock.

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In fact, let's talk about stratum for a moment.

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So if we are connected to an authoritative time source, for example, an atomic

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clock or similar,

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that's considered to be stratum zero.

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So our router, if we're connected to stratum zero, we would be effectively one
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So our router, if we're connected to stratum zero, we would be effectively one

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worse than that.

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That'd be a stratum one.

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So if our time source in the cloud was a stratum zero, we would be a stratum

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one.

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And then if we were a server serving the time down to R3, then R3 would be a

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stratum two

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because it's learning the time from stratum one.

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And that's our three was serving the time down to R5.

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R5 because it's learning the time from stratum two would be a stratum three.

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And that would just continue every hop along the way.

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Think of it like number of hops away from the actual authoritative time source.
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Think of it like number of hops away from the actual authoritative time source.

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So in the lab environment, it helps simulate that.

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I'm going to go ahead and force R1 and R2 to be a stratum one server.

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And the syntax for that is in configuration mode, use the command NTP space

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master

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and then the stratum number that you want them to be.

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So we want these both to be a stratum number one, for example, a pretty trusted

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source for time,

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which is to use that command and global config and boom.

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Both these routers are going to believe their local time that's currently

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configured.

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They're going to consider it authoritative.

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And once that's set up, we can then use them as servers to pass on the time
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And once that's set up, we can then use them as servers to pass on the time

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down to R3 and R4 and et cetera.

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So we're going to start there with making R1 and R2 and NTP stratum level one

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time server for NTP.

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So we're going to use the lab environment.

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I have a lab prepared for you at the tail end of the set of videos.

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So for now, I'm going to double click here on the lab topology to take a look

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at our topology.

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And there it is. Great, great, great.

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And most of our work we're going to do from server one, which has console

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access to all of these devices in our network.

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So we'll go ahead and double click on server one to open that up.
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So we'll go ahead and double click on server one to open that up.

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And we'll give that a moment or two to come up.

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Awesome, there it is.

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And let's go ahead and start here on router ones.

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And with our one selected, let's do a few commands.

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Let's do a show NTP status and press enter.

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And currently we don't have NTP configured yet.

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Let's also show NTP associations.

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And again, because we don't have a configured yet, this is not going to show

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anything useful.

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However, on our one, I do have a debug currently running.

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So if we do a show debug press enter, I'm doing debug NTP everything.
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So if we do a show debug press enter, I'm doing debug NTP everything.

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Same as this pen right here, debug NTP all.

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So if you don't want to debug on, you can turn off with an undibug all.

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I just want the debug on initially so we can see the activity behind the scenes

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as NTP jumps to life.

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So if we want to make this router an NTP server, we simply go into

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configuration mode and type in NTP master.

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Space question mark and then specify the stratum number.

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So I'm going to use one based on our game plan press enter and take a look at

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the debug.

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So it's effectively enabled NTP functionality on all of its interfaces.
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So it's effectively enabled NTP functionality on all of its interfaces.

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It's also using a loop address of 127 as reachable.

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It can reach itself.

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And it's also says I'm synchronized because you just believe the time that it

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currently has.

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So now if we did a show NTP status and press enter.

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So there's our command right there.

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And showing the clock is synchronized to itself.

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It's a stratum one.

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The reference is local means not referring to some other NTP source and has

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other details around the offset and the reference time as well as the pole

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interval.

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So let's go ahead and do the same thing for router two.
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So let's go ahead and do the same thing for router two.

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So we'll go to router two to show NTP status and show NTP associations.

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Nothing there.

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So we'll go into configuration mode and do an NTP master and we'll go to str

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atum of one and we are good to go.

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There's no debug on here.

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So it doesn't have a whole bunch of details behind the scenes.

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But if we now do a show NTP status press center, it says it's synchronized

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pretty easy to synchronize to yourself.

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Just believe your local clock and we do a show NTP associations and press

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center.

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It shows we're synchronizing effectively with the 127 to rest.
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It shows we're synchronizing effectively with the 127 to rest.

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That's our loop back.

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So here in the address college showing who it's synchronizing with it synchron

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izing with itself effectively.

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The little till the symbol right there represents that it's reachable.

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So it's not unexpected that we could reach ourselves if we are the NTP server.

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The reference clock refers to how this server is getting its time and it's

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getting it locally.

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So if there was an external clock at IP address or GPS or atomic clock that

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would be referred to here.

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So the ST is in reference to stratum.

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So up here it shows a stratum level of one because we're getting the time from

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our local system or local clock.
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our local system or local clock.

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Our source of our time is considered to be a stratum level zero.

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In this column, the wind column, it shows how many seconds have passed since

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the last time the NTP server was pulled by the router.

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So even though we're getting the time locally, if we did it again, as far as

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the output,

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it was now seven seconds ago when it pulled itself effectively for the time.

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Here is the pull interval.

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Here is the reachability status.

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So a 377 means that the NTP server that we're referring to.

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In this case, our local clock is reachable.
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In this case, our local clock is reachable.

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The delay represents a round trip delay and because the clock is local on this

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router, there is no delay.

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And the offset is the time difference in milliseconds between the router's

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current time

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and the time provided by the NTP server.

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And the DASP is a shortcut for dispersion.

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It's basically an estimate of the error or the variance in milliseconds between

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the router and the NTP server.

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So even though we're getting the time directly from our own local clock,

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you notice up here it showed 30,937 in change and here it's showing 0.233.
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you notice up here it showed 30,937 in change and here it's showing 0.233.

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And if we did the upper key to show NTP associations again,

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after several pulling intervals, the dispersion went from 3000 down to 0.233.

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And it looks like that's where it's staying.

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And over on the far left, we have a few symbols that might show up as well.

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So the asterisk represents the current NTP server that we are synchronized with

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.

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If there was a pound symbol in front of it that would indicate that the NTP

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server is not reliable

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and regarding synchronization, it would ignore it.

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The plus symbol would indicate that it is a candidate for synchronization,

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but it's not currently the primary source for synchronization.
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but it's not currently the primary source for synchronization.

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And until the on the far left represents that it's reachable.

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And we can see more detail with that same command by just doing a show NTP

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associations detail.

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So we'll press center and that gives us even more detail regarding our

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associations.

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Now NTP is communicated with UTC, universal time coordinated.

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And if you want to see the local time difference on your local routers,

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you just want to use the command to say, please show the offset.

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So right here, for example, on our one and our two, let's go back to our one.

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We did a let me do an undibug all.
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We did a let me do an undibug all.

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And if we did a show, flock press center, that's going to show us in UTC time.

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If we wanted to change that, we could go into configuration mode and somebody

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use the command clock time zone

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and then a label and then the offset that you want from UTC.

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So I happen to be in the United States using Pacific time zone and based on

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when daylight savings is or isn't,

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it may be off by an hour, but I'm going to go ahead and do a dash seven.

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And now if we do a show clock, it's now showing it as 1333 based on the offset
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And now if we do a show clock, it's now showing it as 1333 based on the offset

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of

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dash seven that I just specified.

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So I'm going to go ahead and use that command across all the routers and that

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way I have that consistency there.

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So to do that here in the lab, we can go ahead and click on this little icon up

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here and that brings up a little window.

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I'll do a paste.

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I'll also add a config T on top of that and then end below that and I'll select

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all and then I'll unselect our PCs

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because they aren't going to understand that command.

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So this command is effectively going to set the local time zone on all eight

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routers.

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So we'll click here on send script and it's done.

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Also, just for grants, I'd like to go ahead and look at the clocks on all the
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Also, just for grants, I'd like to go ahead and look at the clocks on all the

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routers.

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Let's do a show clock and then we'll go ahead and send that to every router

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except for PC one PC seven and PC eight because they're not routers.

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We'll click on send script as we look at the time.

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So our ones is 1335 are two 1335 are three 1336.

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So the time isn't perfectly synchronized across all these routers, but they're

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all pretty close.

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So for fun, I'm going to take our one and I'm going to set a slightly different

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time.
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time.

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So let's do a show clock on our one 1336 and let's go ahead and set this maybe

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like 20 minutes off.

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So do that with a clock and a space question mark to make sure on the right

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track and let's do a 13.

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Let's add 20 minutes.

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So 1356 0 0 and I'll still say it's October 16th.

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Oops, I will type of there and fix that.

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So colon 0 0 October 16th 2024.

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So I'm just going to modify it by about 20 minutes and press enter.

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And if we do a show NTB status, it still thinks it's saying anything still good
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And if we do a show NTB status, it still thinks it's saying anything still good

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.

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Trust is local clock, but it's clock is a little faster than the other.

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So in our next step, what we can do is we can go ahead and make, for example,

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let's go look at our topology for a moment.

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Let's make our three a client of our one and we'll make our four a client of

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our two and then we can verify that they can synchronize their time and we

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should also notice that the time on our three.

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Should be bumped up about 20 minutes once that synchronization is completely

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done.

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So let's go to our three and let's make our three an NTB client to our one.
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So let's go to our three and let's make our three an NTB client to our one.

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So that will do a first access to this.

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Let's do a show NTP status.

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Make sure we don't have a configured yet, right?

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We want a configuration mode and to set up our one as our NTP server, we type

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an NTP server and then the IP address.

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Now, because our one has multiple interfaces and has a loop back, it'd be wise

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to point to the loop back interface instead of a physical interface address

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because if we lose a file,

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the physical interface, then we're pointing to that physical interface, we're

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no longer going to get our NTP request answered.

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So let's go ahead and point to our one's loop back address at one dot one dot
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So let's go ahead and point to our one's loop back address at one dot one dot

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one dot one.

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And this also source it from our loop back in our three.

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And that way, even if we lose an interface, we can still communicate out

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existing remaining interfaces once the routing is converged and still reach our

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NTP server.

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So for the NTP server, we'll put in one dot one dot one dot one dot one and we

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'll use a space question mark.

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Then we're going to say source to specify our source interface and that's going

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to be loop back zero, which is our three dot three three address.

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And there's a few other options as well, including the minimum and maximum poll
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And there's a few other options as well, including the minimum and maximum poll

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intervals.

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So I'm going to say the minimum poll interval is four.

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So what that means is two to the power of four to four eight sixteen and I'm

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also going to specify the max poll interval of four, which is also going to be

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two to the power of four, which is sixteen space.

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And then there's also an option for burst.

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Now burst is on by default.

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And what the intent there is that we're going to send multiple requests to our

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NTP servers instead of just one periodically and that should help us to
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NTP servers instead of just one periodically and that should help us to

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synchronize more quickly.

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So that's the syntax we're going to use.

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If we're going to use a key for authentication, we can specify key.

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If we wanted to specify prefer that keyword that would indicate which of our N

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TP servers we prefer if we have multiple configured.

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So now that we've done that, let's do a show NTP status press center and it

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says synchronized.

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Now, if I had done that a few moments earlier, it would very likely would have

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shown that it was not synchronized until I had a few moments to go back and

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forth and synchronized the time.

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So it's considering itself stratum two.

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That's because our reference time server, our one is a stratum one is showing
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That's because our reference time server, our one is a stratum one is showing

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here the reference servers address of one dot one dot one dot one with

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additional details as well.

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So if we did the upper key to show NTP status is still synchronized and

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sometimes you may notice it may go into synchronization and it may go out

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initially as it's starting to synchronize and get itself dialed in.

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So once NTP is in place correctly and the master clock isn't, you know,

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changing widely back and forth and as trusted, we should have synchronization.

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We can also do a show NTP associations of breast center.

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The till the shows us that we have reachability to our NTP server at one dot
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The till the shows us that we have reachability to our NTP server at one dot

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one dot one dot one.

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That server is getting its time from local, meaning itself that server is a str

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atum one.

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And here's our value for reach.

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And as we have more polls that go out, if we get the upper key and do that

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again, that value should increase to the maximum of 377, which means fully

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reachable.

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Here is the round trip delay of 55 milliseconds.

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And here is the current offset, which is the time difference in milliseconds

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between the routers current time and the time provided by the NTP server.
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between the routers current time and the time provided by the NTP server.

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So a super small offset means that the router clock is closely synchronized

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with servers clock and we're going to this little minus sign right there.

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That means that this router is behind a little bit.

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If it was a plus symbol, you mean our time on this local router is ahead.

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So if we hit the upper key and did it again, you'll notice that offset is

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changing and it's getting smaller.

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So we were about 1.9 seconds off, meaning behind the NTP server and now we're

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108 milliseconds off, which is close to a tenth of a second.

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And if we hit the upper key again, and we give it more time, it's also likely
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And if we hit the upper key again, and we give it more time, it's also likely

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to go lower as it gets closer and closer to being synchronized.

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And if we did a show NTP associations detail press center, again, that we get

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as further details about our association with our NTP server.

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So we have a server configured at 1.1.1.1.1. It's sane and valid, effectively

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meaning that its time isn't drastically swinging back and forth.

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There's our pull interval with our delay and offset and other information here

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as well.

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So if we were to take a look at the time on R1 and its client R3, in fact, let
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So if we were to take a look at the time on R1 and its client R3, in fact, let

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's do it right here.

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We'll use this little icon and let's do a show that gives us some space here

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and then we'll do a show clock and then we'll go ahead and run this on R1 and R

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3 and we'll click on Send Script.

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They should have a very close time.

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So R3 is in the 14.08 range and R1 is also very close to that as well.

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Where if we went to R2 and we did a show clock press center, it's showing 13.50

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and that's because we changed the clock on R1 to be in the future about 20

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minutes.

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So let's take the next step and let's make R4 a client of R2.
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So let's take the next step and let's make R4 a client of R2.

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So we'll get R4 and on R4, let's go ahead and do a show NTP status, not set up

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yet.

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Great, we'll do a NTP server.

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Let's use the loopback of 2222 up on R2.

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We'll say source is our own loopback 0 which is our address of 4444.

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Let's also set up the min pull time of 4 and next it means 2 to the power of 4

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which is 16 and a max pull of also 4.

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And let's go ahead and use the keyword of burst, although that's by default, it
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And let's go ahead and use the keyword of burst, although that's by default, it

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's going to be there.

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And to confirm we can do a do, show, run, pipe, include and let's go ahead and

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type in NTP.

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So anything that's default, oops, it's not include.

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So let's go ahead and say include.

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So anything that's a default is not going to show up in the output.

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So as far as the defaults, the burst is a default and the min pull of 4 is also

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a default.

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So the max pull of 4 wasn't a default and that's why it's showing up in the

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output here.

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So if we do a show NTP status press center, it shows that it's unsynchronized

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and a stratum of 16.
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and a stratum of 16.

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So currently it's got a ways to go to synchronize.

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So we do a show NTP associations.

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It can confirm for us that we are configured.

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So the tilde of the represents we have full connectivity to the server 2222 who

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's getting its time from its local self.

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It's a stratum 1 server.

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And if we hit the upper okay a couple times this show NTP status is still unsyn

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chronized, but I believe it's getting closer.

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In fact, let's do this.

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Let's do a debug NTP off and let's take a look.

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In fact, let's also go ahead and remove the config and put it back so we can

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see the play by play.

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So let's do a do show run include NTP and I'll do a no in front of that.
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So let's do a do show run include NTP and I'll do a no in front of that.

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Oh, look at that.

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So it just said clock synchronized with the NTP server.

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So I am not going to remove that and have it come back back.

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You know what?

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Let's just watch it again with the debug.

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So we'll do a no and I want NTP server 2222 and then we'll do a NTP server 2222

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source loop back zero and we'll go ahead and use keyword burst and press center

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.

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All right.

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So let me go ahead and turn off the debug here real quick.
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So let me go ahead and turn off the debug here real quick.

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We'll do a do an all and as I was going through these debug earlier, I saw this

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really fun one right here popcorn popcorn.

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So, but what that means is not quite synchronized yet.

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So that's what that means like that.

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Why did they put that there?

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So someone had a sense of humor.

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So popcorn popcorn means it's still synchronizing and right there that last

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message right there indicates that it's now synchronized.

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So if we do a show NTP status press center here, showing us status of

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synchronized and we are stratum 2 and that's because we're synchronized to a
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synchronized and we are stratum 2 and that's because we're synchronized to a

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stratum 1 server.

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We can verify that with a show NTP associations press center and that confirms

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were synced up with a stratum 1 server and for more information that we can do

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a show NTP association detail and press center.

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So if we look at the clocks here on our two and our four, they should be very,

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very close. So we'll go ahead and use the tool here to then that command our

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two and our four at the same time.

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Let's do a show clock and then we'll send that to our two and our four.

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They're both selected will click on send script and there's our four 1357 and
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They're both selected will click on send script and there's our four 1357 and

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our two 1357 extremely close to each other because our two is the server and

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our four is synchronized to our two.

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Now another option we have with NTP is the option of today of NTP peers. Now

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the benefit of that is that if we lose our more authoritative time servers like

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for example stratum 2 or stratum 1 server, we can have our devices running NTP

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peering with each other.

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So at least they're not completely cut off from any option of learning and

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hopefully correcting to the accurate time.

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So I'll walk into configuring and verifying NTP peers in the very next video.
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So I'll walk into configuring and verifying NTP peers in the very next video.

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So see you there in just a moment.