Cisco IP SLA Monitor or just IP SLA?

Cisco IOS IP Service Level Agreements (SLAs) help network administrators ensure that a high level of voice and data communication quality is maintained. Cisco IP SLA operations are a proactive method of reliably measuring network performance. IP SLA data can be retrieved and trended with an SNMP Performance trender to enable users to graph performance over time. Cisco IP SLA and SNMP should be in the tool belt of every network administrator. Pair these technologies with a NetFlow analyzer and you’ve got a great setup to help troubleshoot most network problems.

The purpose of this blog is to outline some of the IP SLA configuration changes in newer versions of Cisco’s IOS.

We’ve written a 4-part blog in the past that focuses on the following IP SLA operations:

Cisco IP SLA Jitter:
Probably one of the most important IP SLA operations for monitoring VoIP communications. When used with a responder, it allows users to retrieve metrics for Latency (to and from – source and destination ). Jitter, which is described as packet delay variance or the difference between source and destination latencies. Mean opinion scores (MOS) and ICPIF scores are generated to grade VoIP quality of communication. Several different types of packet loss and more.

Cisco IP SLA ICMP Echo:
IP SLA Operation measures end-to-end response time between a Cisco router and any device with an IP address.

Cisco IP SLA TCP Connect operation:
One can consider this to be a ping over TCP.

Cisco IP SLA HTTP:
The HTTP IP SLA operation is a very useful tool in the verification of performance of Web servers, Proxy servers, or any other HTTP server. Three metrics of performance attained by the HTTP operation are DNS Lookup, TCP Connect, and HTTP Transaction times.

There are white papers on IP SLA Configuration to help configure all four of these available for free on our site. If you don’t have them, you should get them. They’re a great reference to have on hand.

The reason I wanted to bring this up today is to talk about the actual configuration of the IP SLAs. There are slight variations between different versions of CISCO IOS regarding the configuration of the IP SLA operations.

We’ve found that in some of the more modern versions of Cisco IOS, the IP SLA commands that contain the word “Monitor,” according to the Cisco’s IP SLA configuration guide, no longer accept a command with the word “monitor” in them.

For example, let’s take a look in the Cisco IOS IP SLAs Configuration Guide, Release 12.4 (The Jitter section explains how to configure an IP SLA Jitter operation).  On page 3 of the guide, it states that the IP SLAs Responder must be enabled on the target device. It goes on, giving the example as:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Router (config)# ip sla monitor responder

In some of the more modern IOS versions, the correct command is:

Router (config)# ip sla responder

On the next page of the same document you’ll see that to create an IP SLA operation begins with:

 

 

 

 

Router (config)# ip sla monitor operation-number

In the more modern IOS versions the correct command is:

Router (config)# ip sla operation-number

 

Also notice that in the screenshots above, you need to specify which type of IP SLA you want to create.

The Cisco documentation says:

Router (config-sla-monitor)# type

Where in the new versions, the word “type” is not an option. You simply state which type you are using:

Router (config-ip-sla)# udp-jitter

Lastly, the “no ip sla monitor operation-number” has been changed to “no ip sla operation-number.”

So if you’re having issues configuring IP SLA operations, you may be on the newer code. As a rule of thumb, if your router does not accept the IP SLA commands with “monitor” in the command, simply exclude it and try again. The ” ? ” is your friend. Use the ? when configuring IP SLAs to see the next list of available options.

Now, before each of these variations of older IOS versions were using “rtr,” which was then replaced by “ip sla Monitor.”  In my opinion, the the IP SLA operations have been much improved since the earlier versions. Keep in mind that some SNMP OIDs are also different from earlier versions.

For example:
“rtr responder” was replaced with “ip sla monitor responder”
“show rtr operation-state” was replaced with “show ip sla monitor statistics”
to create the monitor – “rtr” was replaced with “ip sla monitor”

Check out the Cisco IOS IP Service level agreements command line Interface white paper for more details on the older commands.