So currently we have R1 and R2 as NTP servers at Stratum 1.
We have R3 as they client to R1 and R4 as they client over to R2.
So if we had R1 and R2 synchronizing with some external atomic clocks or time
servers out on the
internet that were Stratum 0, what happens if one of those is no longer
available?
We don't want those key servers to give up regarding time.
We still want them to have a way of synchronize or if R3 and R4, if they lose
connectivity,
for example to R1 and R2. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
for example to R1 and R2.
So think of a peer as like a backup friend you can go to in the event that the
time server that
you are synchronizing with is no longer reachable.
And that way these two devices can ask of the time of each other if they need
to and then
synchronize their time that way.
So for the demo I'm going to go ahead and specify that R3 is going to be a peer
with R4
and R4 is going to appear with R3.
Now because they're both getting their time from a Stratum 1 NTP server,
they're going to actually start querying each other and actually believing the
information from WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
information from
each other until they lose connectivity to their respective time servers at Str
atum 1.
And it'd be at that point that they start reaching out and asking for the time
and
synchronize the time with their peer.
Think of it like a fault tolerance or a fallback method for making sure that we
have the correct
time even if our primary time servers fail.
So with that in mind, let's head over to R3 and then R4 and we'll set them up
as NTP peers.
So back in the lab, let's go to R3.
We'll start there and on R3, let's go ahead and do a show debug. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
We'll start there and on R3, let's go ahead and do a show debug.
And let's do a debug of NTP everything.
So debug NTP all and I'll do the same thing on R4.
We'll do a debug of NTP all.
And let's also verify where we're at as far as NTP by going to R3.
I'm doing a show NTP status.
Fantastic.
We're synchronized with the server at 1111.
Let's also do a show NTP associations press center.
Here it shows we are configured to use 1.1.1.1 as our time source and little
asterisk here at the
far left means that we're synchronizing with that server. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
far left means that we're synchronizing with that server.
All right.
So to configure R4 as an NTP peer, in fact, let me go do a do on debug all and
then we can look
at the debug over on R4 if we need to.
So here we'll do an NTP and instead of specifying server, we're going to go
ahead and specify
peer.
That's this option right here.
So NTP peer will put in the IP address of the loopback on R4, which is 4.4.4.
We'll specify the source for our packet address.
And over there is the IP address on our loopback zero interface. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
And over there is the IP address on our loopback zero interface.
So we'll put that in and then we can also go ahead and specify things like the
men
pull time on put four, which is which is two to the power four, which means 16
and the max
pull also at the same value.
And I'm also going to say burst, even though I think it's on by default and we
'll press
center and then we'll do a similar treatment over at R4.
So we'll go to R4 and on R4, we'll go config T and we'll type in NTP peer and
put in 3,
3, 3, 3, source, loopback zero, men timer, four and max timer, four for the lab WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
3, 3, 3, source, loopback zero, men timer, four and max timer, four for the lab
and then the keyword
of burst.
So now if we do this show, in fact, let me turn off debugging here as well.
Do an unall as a show NTP status.
So notice that we are still, oh, check it out.
We got it during a decision point.
So it is not synchronized at the moment.
Let's give it a moment to go ahead and correct that will do a show NTP status.
And while we're waiting for the synchronize will do a show NTP associations and
press center.
So here, you'll notice there's no asterisk on the left hand side. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
So here, you'll notice there's no asterisk on the left hand side.
So it knows about two, two, two, two, which is a stratum one server.
It knows about three, three, three, three as a peer and it's a stratum two
server.
So after we give it a few more moments here, it should once again synchronize
its clock back to two,
two, two, and then also be aware that three, three, three, three exists as well
.
And let's go to our three and over here on our three with debugging not on list
to a show NTP status,
press center.
And that guy is synchronized to the server at 1111.
And if we do a show NTP associations and press center, WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
And if we do a show NTP associations and press center,
here we have the asterisk next to the 1111 indicating that we are synchronized
with that NTP server.
However, we still have our four in the wings in case our primary server goes
away.
And we can synchronize with it.
So let's go back to our four and one of the verify that our four is synced up.
So let's show NTP status press center and it still says unsynchronized.
So a couple options here.
We could just wait, which is perfectly fine.
If you want to do some debug like debug NTP all press center.
We could look at the debug messages. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
We could look at the debug messages.
We could do a show NTP status.
So we are communicating with R2.
That's great.
And at some point in time, we will synchronize once again with our primary NTP
server,
the stratum one server, which is part two.
And another option is let's do a do undibug all as to a do show run include NTP
.
Now this part right here is really just to keep us busy while we're waiting for
NTP to
synchronize because by itself it will just synchronize.
But if you're impatient or want to force it, one thing I've discovered over the WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
But if you're impatient or want to force it, one thing I've discovered over the
years is that
if we take out the configuration, put it back in, that's often very helpful.
So let's go ahead and do a no.
And I'm going to take off the NTP server here, no NTP server at 222.
And then I'll put it back in with the right click and we are back in business.
Also, I didn't specify the min and max timers.
So if we wanted to, we could go ahead and do that with a min of four and a max
of four
and versus on by default, but if it makes us feel better, we can try to force
it that way
and then just give it a little bit of time. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
and then just give it a little bit of time.
So again, if you did the debug of NTP all press center,
that would help us identify what's going on that we're actually communicating
back and forth
with the respective other NTP devices.
And once it says that the clock is synchronized, it'll also show up in the show
NTP status
that the clock is synchronized to the NTP server over at R2.
So I'm going to do an debug all and show NTP status.
Oh, there we go.
Oh my gosh.
We just turned off the debug before I got the message about synchronization.
So we are now synchronized back to R2 and we do a show NTP associations and WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
So we are now synchronized back to R2 and we do a show NTP associations and
press center.
Here we have the little asterisk indicating we are synchronized with a server
and the tilde represents we have full communication back and forth with that
device.
And again, if we do a show NTP status, it'll confirm for us that we are
synchronized with our
server.
So if you're working with a Cisco device and you're working with an NTP server,
you'd want to make sure a few things are going your way.
Number one, are the ports for NTP? Are they open and available?
Meaning are we allowing UDP port 123?
So if we went up to R1, for example, or R2, WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
So if we went up to R1, for example, or R2,
and we did a show control plane host open ports and press center,
you'll notice that UDP port 123 is open in listen mode because we're acting as
an NTP server.
So we want to make sure if we have firewalls or anything else in place between
our NTP clients
and our NTP servers, we want to make sure that we're allowing those specific
protocols through
so NTP can operate.
And we also want to incorporate some fault tolerance such as NTP peers and
multiple NTP servers that we can communicate with.
So if we have a failure of one device in our network, it's not going to ruin WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
So if we have a failure of one device in our network, it's not going to ruin
our time stamps
across the board.
So now that we looked at the NTP configuration as well as some confirmation
that is working,
in the next video, I'd like to put you, my friend, on a hands-on lab so you can
get up close and
personal hands-on practice and build your skills in working with the
configuration
and verification of network time protocol.
So when you're ready, I'll see you in the next video in just a moment.