Assess Service Level Agreements using IP SLA

Service Level Agreements (SLA) are constantly being pushed to the upper limits as we add more and more traffic to our enterprise network. VoIP, customer relationship management (CRM), VPN, and other business related traffic, are just some of the different ways we are using our networks today, and we continue to come up with different ways to use our network. We have to be able to take measures to make sure that our SLA is being honored, and if not we can have solid proof that it isn’t. Echo Request (Ping) is a great tool for verifying Layer 3 connectivity, even the extended ping doesn’t do what we need. We need to be able to gather information over time at scheduled intervals, in order to get viable data.

Fortunately, IOS has a feature for this specific task (Thanks Cisco). Aptly named, IP SLA, allows you to assess your SLA over an IP network using IOS. IP SLA can track various metrics and report back statistics for a given period of time, days, hours, etc. Very useful when making sure a SLA is in place.

The topology of IP SLA consists of a head end and a responder. The responder sends packets to the head end and the head end replies, as the responder receives replies, it time stamps them.

First, we will have to setup a responder. There are a number of different modes that IP SLA responder can be used depending on the version of IOS. I am going to use udp-echo for my configuration.

SC-R(config)#ip sla responder udp-echo ipaddress port 5000

That is it? Yup, one command to setup the responder. Next, we will setup the head end, which consists of creating an IP SLA operation (similar to a policy-map) and apply it with a schedule. I am only using the basic udp-echo for this operation, but you can test other services like DHCP, DNS,  HTTP, MPLS, VoIP, and a load of other generic operations.

SC-H(config)#ip sla 26
SC-H(config-ip-sla-jitter)#frequency 30

Now that we have a IP SLA policy configured we have to apply it with a schedule (think cronjob).

SC-H(config)#ip sla schedule 26 start-time now life forever


Lets verify that our SLA is working as it should.

SC-H#show ip sla statistics 26 details 

Round Trip Time (RTT) for       Index 26
        Latest RTT: 2 milliseconds
Latest operation start time: 19:15:52.441 AST Tue Feb 15 2011
Latest operation return code: OK
Over thresholds occurred: FALSE
Number of successes: 42
Number of failures: 0
Operation time to live: Forever
Operational state of entry: Active
Last time this entry was reset: Never


Seems like our SLA operation is running and collecting data, awesome.

While doing a little searching around on Google I came across this free IP SLA Monitor tool from SolarWinds, I haven’t tried this product myself, but it looks promising and it’s free, the right price for everyone 🙂


Feb 15th, 2011 • Posted in IOS, Reporting
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