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IP SLA UDP Jitter : values on RTT = 1ms

Frederic RIBES

Hi all !

From several Cisco router (IPSLA sender) and whatever the target router (IPSLA responder receiver), the values regarding round trip time (RTT) are false (always equals to 1ms) as you can see below :


Round Trip Time (RTT) for       Index 718

        Latest RTT: 1 milliseconds

Latest operation start time: 16:36:15.271 GMT+1 Mon Jan 20 2014

Latest operation return code: OK

RTT Values:

        Number Of RTT: 10               RTT Min/Avg/Max: 1/1/1 milliseconds

Latency one-way time:

        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

Jitter Time:

        Number of Jitter Samples: 9

        Source to Destination Jitter Min/Avg/Max: 16/19/24 milliseconds

        Destination to Source Jitter Min/Avg/Max: 2/2/2 milliseconds

Packet Loss Values:

        Loss Source to Destination: 0           Loss Destination to Source: 0

        Out Of Sequence: 0      Tail Drop: 0    Packet Late Arrival: 0

Voice Score Values:

        Calculated Planning Impairment Factor (ICPIF): 0

        Mean Opinion Score (MOS): 0

Number of successes: 5

Number of failures: 0

Operation time to live: Forever


sh run IPSLA :

ip sla 662

udp-jitter xx.xx.xx.xx

owner xxx

frequency 300

ip sla schedule 662 life forever start-time now ageout 60

MTU set on interface on IPSLA sender router = 1500

IOS version for IPSLA sender router : C850 Software (C850-ADVSECURITYK9-M), Version 12.4(4)T6 & 1841 Software (C1841-ADVIPSERVICESK9-M), Version 12.4(25b)

What I have found on Cisco Debug Toolkit :

Unfortunately, I can't increase MTU as requested since it is already = 1500 :-(

Any support ?

Thanks in advance.

2 Replies 2

Frederic RIBES


Frederic RIBES

A bug on the IPSLA measures has been detected on some versions of Cisco IOS 15.X.

An IPSLA bug affecting some versions of Cisco IOS 15.X has been detected resulting in the report of incoherent network delays.


The bug concerns the IPSLA Responder that may be enabled on routers of your operators. The responder implements the measure IPSLA Jitter that calculates the network delays or RTT (Round Trip Time).

Result: an incoherent RTT, which can be fixed at 1ms or variable but with low values. The RTT is the time to reach the target and the time for the target to respond. In the affected versions, it does not match at all.

Example of results with incoherent measures related to Cisco bug:

- A measure with a time to reach and return of 80ms and 100ms gives a 20ms RTT!

- A measure with a constant 1ms RTT, time to reach and return of 80ms and 100ms time!

- A measure between France and Australia with a 10ms RTT!

List of the versions which correct this bug

The Cisco support has confirmed this bug and given the following list of versions not affected by the bug:

  • 15.3(3)M3
  • 15.3(2.25)M0.1
  • 15.4(0.7)S
  • 15.4(0.1)T
  • 15.3(2.25)T
  • 15.3(3)M0.1
  • 15.3(3)M
  • 15.3(3)S
  • 15.3(2)T1.3
  • 15.3(2)T2
  • 15.3(3)S2
  • 15.2(1)IC273.5
  • 15.2(4)M5.6
  • 15.2(4)M6
  • 15.1(1)ICA4.122
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