5.7 Configure and verify NTP operating in a client/server mode

Having accurate time on interconnected devices is essential for troubleshooting, security and general sanity. Differences in time between machines even if small can lead to increased difficulty in troubleshooting.

Having accurate and synchronized time on all devices should be part of the basic setup of networking devices. In this lab I used a real NTP server on the internet as the master clock for the simulated network that I built.

Let’s start with the following topology:

Screenshot_2018-10-30_08-42-51

I have used VLSM on each device and loopback interfaces. OSPFv2 has been configured with all devices in area 0. Loopback interfaces have been set as passive:

!!! R1 config excerpt
interface Loopback1
 ip address 172.16.0.1 255.255.255.0
 ip ospf 1 area 0
!
interface GigabitEthernet0/0
 ip address 10.255.255.245 255.255.255.252
 ip ospf 1 area 0
 duplex full
 speed 1000
 media-type gbic
 negotiation auto
!
router ospf 1
 log-adjacency-changes
 passive-interface Loopback1
!

Next NAT has been configured inside GNS3:

!R1 excerpt
interface GigabitEthernet1/0
 ip address dhcp
 negotiation auto
!
ip name-server 1.1.1.1

The internal loopbacks of each router have been set to 172.16.0.x (x being the router number):

!R1
r1#show ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area 
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route

Gateway of last resort is 192.168.122.1 to network 0.0.0.0

C    192.168.122.0/24 is directly connected, GigabitEthernet1/0
     172.16.0.0/16 is variably subnetted, 4 subnets, 2 masks
O       172.16.0.4/32 [110/3] via 10.255.255.246, 00:15:08, GigabitEthernet0/0
C       172.16.0.0/24 is directly connected, Loopback1
O       172.16.0.2/32 [110/2] via 10.255.255.246, 00:36:13, GigabitEthernet0/0
O       172.16.0.3/32 [110/3] via 10.255.255.246, 00:36:13, GigabitEthernet0/0
     10.0.0.0/30 is subnetted, 3 subnets
O       10.255.255.248 
           [110/2] via 10.255.255.246, 00:36:13, GigabitEthernet0/0
O       10.255.255.252 
           [110/2] via 10.255.255.246, 00:15:08, GigabitEthernet0/0
C       10.255.255.244 is directly connected, GigabitEthernet0/0
S*   0.0.0.0/0 [254/0] via 192.168.122.1

Next we set R1 as the master and set R1 to get it’s updates from the real world:

ntp master 2
ntp server 0.au.pool.ntp.org

On each router set the timezone (I live in Queensland):

clock timezone AEST 10

Next on all other routers except R1:

ntp server 172.16.0.1

Verify using “show” commands:

r1#show ntp status 
Clock is synchronized, stratum 3, reference is 27.124.125.251
nominal freq is 250.0000 Hz, actual freq is 250.0000 Hz, precision is 2**24
reference time is DF820DE6.0CFC0557 (08:53:26.050 AEST Tue Oct 30 2018)
clock offset is -0.0034 msec, root delay is 0.14 msec
root dispersion is 0.20 msec, peer dispersion is 0.06 msec
loopfilter state is 'CTRL' (Normal Controlled Loop), drift is -0.000000002 s/s
system poll interval is 128, last update was 249 sec ago.
r1#show ntp associations 

  address         ref clock       st   when   poll reach  delay  offset   disp
 ~127.127.1.1     .LOCL.           1      0     16   377  0.000   0.000  0.232
*~27.124.125.251  130.217.226.51   2    121    128   177 76.126  -3.484 65.310
 * sys.peer, # selected, + candidate, - outlyer, x falseticker, ~ configured
r1#

r2#show ntp status 
Clock is synchronized, stratum 3, reference is 127.127.1.1   
nominal freq is 250.0000 Hz, actual freq is 250.0000 Hz, precision is 2**24
reference time is DF829B5E.91AD1430 (18:57:02.569 AEST Tue Oct 30 2018)
clock offset is 0.0000 msec, root delay is 0.00 msec
root dispersion is 0.00 msec, peer dispersion is 0.00 msec
loopfilter state is 'CTRL' (Normal Controlled Loop), drift is 0.000000003 s/s
system poll interval is 16, last update was 5 sec ago.
r2#show ntp associations 

  address         ref clock       st   when   poll reach  delay  offset   disp
*~127.127.1.1     .LOCL.           2      6     16   377  0.000   0.000  0.240
 ~172.16.0.1      27.124.125.251   3     40     64   177  4.363 -359793  3.376
 * sys.peer, # selected, + candidate, - outlyer, x falseticker, ~ configured
r2#



That’s it! Now enjoy synchronized time.

Screenshot_2018-10-30_08-38-59.png

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