04-22-2019 01:12 AM
We have configured IP SLA on two of our devices [ASR 1K and ISR 3900] for latency measurement, but can't get "one-way delay", could you please take a look at the configuration and advise what's the potential problem?
ROUTER_ASR>
ip sla 121
udp-jitter 10.251.64.4 5000 source-ip 10.234.128.24 num-packets 100
request-data-size 36
tos 104
frequency 300
IPSLA operation id: 121
Number of Latency one-way Samples: 0
Source to Destination Latency one way Min/Avg/Max: 0/0/0 milliseconds
Destination to Source Latency one way Min/Avg/Max: 0/0/0 milliseconds
ROUTER_ASR>show ntp assoc
address ref clock st when poll reach delay offset disp
*~146.170.96.220 146.170.124.36 4 612 1024 377 235.96 -1.446 30.399
+~146.170.56.220 146.170.124.36 4 922 1024 377 223.97 -2.407 30.382
* sys.peer, # selected, + candidate, - outlyer, x falseticker, ~ configured
ROUTER_ASR>show ntp status
Clock is synchronized, stratum 5, reference is 146.170.96.220
nominal freq is 250.0000 Hz, actual freq is 249.9962 Hz, precision is 2**6
reference time is E04D6361.BC6A8100 (04:28:17.736 GMT Tue Apr 2 2019)
clock offset is -1.4462 msec, root delay is 238.81 msec
root dispersion is 138.80 msec, peer dispersion is 30.39 msec
loopfilter state is 'CTRL' (Normal Controlled Loop), drift is 0.000014998 s/s
system poll interval is 1024, last update was 619 sec ago.
ROUTER_ISR >
ip sla 121
udp-jitter 10.234.128.24 5000 source-ip 10.251.64.4 num-packets 100
request-data-size 36
tos 104
frequency 300
IPSLA operation id: 121
Number of Latency one-way Samples: 0
Source to Destination Latency one way Min/Avg/Max: 0/0/0 milliseconds
Destination to Source Latency one way Min/Avg/Max: 0/0/0 milliseconds
ROUTER_ISR>show ntp assoc
address ref clock st when poll reach delay offset disp
*~146.170.56.220 146.170.124.36 4 51 1024 377 204.49 76.934 0.070
+~146.170.96.220 146.170.124.36 4 409 1024 377 215.90 76.070 0.091
* sys.peer, # selected, + candidate, - outlyer, x falseticker, ~ configured
ROUTER_ISR>sh ntp status
Clock is synchronized, stratum 5, reference is 146.170.56.220
nominal freq is 250.0000 Hz, actual freq is 249.9989 Hz, precision is 2**22
ntp uptime is 1103784700 (1/100 of seconds), resolution is 4016
reference time is E04D55A1.22308841 (03:29:37.133 GMT Tue Apr 2 2019)
clock offset is 76.9345 msec, root delay is 219.80 msec
root dispersion is 192.68 msec, peer dispersion is 0.07 msec
loopfilter state is 'CTRL' (Normal Controlled Loop), drift is 0.000004097 s/s
system poll interval is 1024, last update was 4279 sec ago.
I assume the issue is due to the clock offset being way too high. So, the solution is to synchronise the devices. How do i achieve this ?
Thank you. Any help would be really appreciated.
04-22-2019 08:14 AM
I should sync the clocks either by using a better ntp source (http://support.ntp.org/bin/view/Servers/WebHome) other people also mentioned using the "clock-tolerance" command, but I have not tested it.
The source and destination are not on the same subnet, but are the devices directly connected? It is possible the IP SLA could be rounding the values to 0 if the OW delay is < .5 ms.
Rolando A. Valenzuela
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