Networking

IP SLA Basics

Cisco IP SLA sends test traffic to measure delay, jitter and loss. The operation types, a one line responder config, and the UDP jitter probe with a G.711 codec I run in production.

Tony Mattke · 2011.05.06 · 3 min read

IP SLA is a function of Cisco’s IOS enabling you to analyze a Service Level Agreement (SLA) for an IP application or service. IP SLAs use active traffic-monitoring to continuously monitor traffic across the network. This is very different from SNMP or Netflow data which give you more volume oriented statistics. Many different metrics can be analyzed using IP SLA, here is a break down of a few.

  • UDP Jitter – Probably the most used operation in all of IP SLA. This IP SLA generates UDP traffic and measures Round-trip Delay, One-way Delay, One-way Jitter, One-way Packet Loss, and overall Connectivity.
  • ICMP Path Jitter – Hop-by-hop Jitter, Packet Loss, and Delay.
  • UDP Jitter for VoIP – Enhanced test for VoIP monitoring. It can simulate various codecs and spits out voice quality scores (MOS, and ICPIF). Also shows us Round-trip Delay, One-way Delay, One-way Jitter, and One-way Packet Loss.
  • UDP Echo – Round-trip Delay for UDP traffic.
  • ICMP Echo – Round-trip Delay, full path.
  • ICMP Path Echo – Round-trip Delay and Hop-by-hop round trip delay.
  • HTTP – Round-trip time using simulated http traffic.
  • TCP Connect – Allows us to sample the time to connect to a target using TCP.
  • FTP – Round-trip time for file transfers.
  • DHCP – Round-trip time for dynamic host configuration.
  • Frame-Relay –Round-trip Delay, and the Frame Delivery Ratio. Mostly used for circuit availability.

IP SLA Configuration

There are 2 parts to the IP SLA configuration. Our testing source, and the responder. Typically our responder is a device local to the data center, while the test host is device at a remote site. The test host sends data to the responder and the responder sends a reply back. The configuration for the responder is nothing but really, really simple…

text
ip sla responder

Seriously. Now lets take a look at the configuration of the testing source. Any questions I don’t answer here should be easily available via IOS context help… Here is an example I’m using in production.

text
ip sla 10                                                        ! New IP SLA Instance #10
  udp-jitter 10.1.1.1 16800 source-ip 10.2.2.2 codec g711ulaw    ! udp jitter w/Voice codec
  tos 184                                                        ! TOS bit, using EF here
  frequency 300                                                  ! testing interval
ip sla schedule 10 life forever start-time now                   ! start now, never stop

So, what does this get us? Here are the stats output by our IP SLA source..

text
Router#sh ip sla statistics 10    ! Omit the # to view all SLA stats.
IPSLAs Latest Operation Statistics

IPSLA operation id: 10
Type of operation: udp-jitter
        Latest RTT: 42 milliseconds
Latest operation start time: 18:28:06.603 UTC Thu May 5 2011
Latest operation return code: OK
RTT Values:
        Number Of RTT: 1000             RTT Min/Avg/Max: 39/42/154 milliseconds
Latency one-way time:
        Number of Latency one-way Samples: 1000
        Source to Destination Latency one way Min/Avg/Max: 25/26/41 milliseconds
        Destination to Source Latency one way Min/Avg/Max: 13/15/127 milliseconds
Jitter Time:
        Number of SD Jitter Samples: 999
        Number of DS Jitter Samples: 999
        Source to Destination Jitter Min/Avg/Max: 0/2/15 milliseconds
        Destination to Source Jitter Min/Avg/Max: 0/2/90 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  Packet Skipped: 0
Voice Score Values:
        Calculated Planning Impairment Factor (ICPIF): 1
MOS score: 4.34
Number of successes: 7
Number of failures: 0
Operation time to live: Forever

Conclusion

Cisco’s IP SLA features can be a huge benefit to any engineer trying to track down issues on the network. Using IP SLA in combination with a SNMP management suite, or even an EEM script can provide real time alerting for adverse network conditions, allowing you to respond faster and perform better.

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Comments

15 archived comments from Disqus 2011–2016
Guest
Nice summary of the technology - just a shame that Cisco’s flagship Nexus range still doesn’t support it.
Josh
What IOS version are you using? My command set is quite different.
dakna adnane
brief & efficient.
mike
10x for a great article .
Cristian
Nice article… Just a question… In the testing source side, the IP address 10.1.1.1 always correspond to the Responder, right?
net

hi

how do we calculate the memory usuage per ip sla session

MIke

HI

How can I know to which extent the responder is able to process the requests/probes ? How many probes per second can a responder process ?

Ramesh
Can any one tell me - is there is a possibility that the TOS bit can reset along the network path???
ait ben hadou
thank you for writing this great post
khalid

hi
can any one help how to calculate RTT ?
ip sla 4 tcp-connect <I.P> <Port > source-ip <> source-port <> threshold
timeout frequecy

sh ip sla Static
? every router show different RTT is there any way fix RTT ? ip sla reaction-triger ……… it does not work for me Or any link which will help us to knwo how tocalculate ? Please now link for cisco help site ? documentation very bad . thank you in adavance

Anup
Thanks for the very simple IP SLA Explanation. Very informative !
Ahmad

Hi,

I am unable to get one way delay statistics. The source and target are synchronized to NTP server. Another strange thing is that the value of jitter that it shows is greater than the maximum RTT value.

IPSLA operation id: 400

Type of operation: udp-jitter

    Latest RTT: 1 milliseconds

Latest operation start time: 06:03:10 UTC Sun Aug 9 2015

Latest operation return code: OK

Over thresholds occurred: FALSE

RTT Values:

    Number Of RTT: 200              RTT Min/Avg/Max: 1/1/10 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

    Source to Destination Latency one way Sum/Sum2: 0/0

    Destination to Source Latency one way Sum/Sum2: 0/0

Jitter Time:

    Number of SD Jitter Samples: 199

    Number of DS Jitter Samples: 199

    Source to Destination Jitter Min/Avg/Max: 3/67/983 milliseconds

    Destination to Source Jitter Min/Avg/Max: 0/1/3 milliseconds

    Source to destination positive jitter Min/Avg/Max: 902/952/983 milliseconds

    Source to destination positive jitter Number/Sum/Sum2: 7/6668/6358044

    Source to destination negative jitter Min/Avg/Max: 3/33/502 milliseconds

    Source to destination negative jitter Number/Sum/Sum2: 192/6516/545438

    Destination to Source positive jitter Min/Avg/Max: 1/1/3 milliseconds

    Destination to Source positive jitter Number/Sum/Sum2: 59/69/91

    Destination to Source negative jitter Min/Avg/Max: 1/1/3 milliseconds

    Destination to Source negative jitter Number/Sum/Sum2: 56/68/94

    Interarrival jitterout: 0       Interarrival jitterin: 0

    Jitter AVG: 34

Packet Loss Values:

    Loss Source to Destination: 0

    Source to Destination Loss Periods Number: 0

    Source to Destination Loss Period Length Min/Max: 0/0

    Source to Destination Inter Loss Period Length Min/Max: 0/0

    Loss Destination to Source: 0

    Destination to Source Loss Periods Number: 0

    Destination to Source Loss Period Length Min/Max: 0/0

    Destination to Source Inter Loss Period Length Min/Max: 0/0

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

Packet Skipped: 0

Voice Score Values:

    Calculated Planning Impairment Factor (ICPIF): 0

    Mean Opinion Score (MOS): 0

Number of successes: 3

Number of failures: 0

Operation time to live: Forever

Operational state of entry: Active

Last time this entry was reset: Never

Any help would be much appreciated….

Regards Ahmad

Tudor
nice article :)
Homes_Atrocious
Excellent explanation. IP SLA really is an awesome tool, not just for monitoring, but for implementing PfR.
Pablo Muñoz
Hi, good post. I have a question, is it possible to do ip sla from a Linux machine?