IP SLA: How to Automate WAN Links for Best Redundancy


IP SLA is an IP Server Level Agreement. It is a feature of Cisco Router’s IOS to provide real-time network traffic monitoring performance and reporting. Moreover, it can report network metrics like basic connectivity, delay, jitter, packet loss frequency response time, etc.,

            It is a great tool for ISPs to monitor their customer sites or they can use it within their network for network troubleshooting. It is also a helpful tool for troubleshooting our network. There is no need for a physical probe to monitor the network performance.  A probe is a measurement that is conducted across the network to assess the performance and reliability of a network. A set of packets which is also known as the probe is sent across the network to gather data on key performance metrics such as delay, jitter, and packet loss.

            There is a need for source and optionally responder in IP SLA configuration. Its source is generally in the form of packets and sends those packets to a destination. The source packets will be of different types, such as an ICMP echo, which is used to continuously test the reachability of a remote device. The responder from the remote device would have time-stamp information based on which IP SLA will make calculations about specific network metrics for which we are interested.

            We can configure a remote Cisco device as an IP SLA responder optionally. So it will enable the remote device to respond more advanced to IP SLA request packets—however, some of its operations work without the responder.

            For IP SLA to be effective, they leverage SNMP traps triggered by events, such as delay, jitter, packet loss, and connection loss, just to name a few things. We set certain threshold limits for IP SLA. The threshold such as specific round time trip metric. If our IP SLA detects some threshold violation, that is, if the round trip time exceeds our configured upper limit, then an SNMP trap would be sent out to trigger an alert to a network administrator.

Lab Topology for IP SLA

Lab topology for IP SLA

Configuration of static route

Static route configuration

Ping R2 Loopback 0 from R1 Loopback 0.

ping R2 from R1

Configuration on R1

IP SLA configuration

In the first command, the “1” indicates IP SLA number. The 2nd command ICMP-echo is used to test the IP address continuously from the source interface, Loopback 0 of R1. The threshold 2 means if the calculated measurement exceeds the value of 2, the IP SLA operation will trigger a threshold crossing event. the timeout is 10000 milliseconds. This is the maximum amount of time the operations are allowed to take before being considered a failure. The frequency 3 means, the operation will be repeated every 3 seconds.

Check the statistics

show IP SLA statistics

Track the first static route that is pointing to If this route goes down, then it traces continuously the 2nd one which is pointing to

track 1 ip sla reachability

The keyword reachability specifies that the tracking object is tracking the reachability status of the associated IP SLA operation. While track 1 is in the default route, the route is being tracked by the previously defined tracking object with number 1.

Check or verify the static route

show static route

I am going to shut down the Router R2 fast Ethernet 0/0 as

R2(config)#interface fast Ethernet 0/0

R2(config-if) #shutdown

As R1 continuously tracks the static route, it will take the backup static route and make it a primary route to the destination.

show ip route

Also, check its statistics.

show ip sla statis

Show track

show track

Enable fast Ethernet 0/0 of Router R2 and then run the following command.

show track

Check the static route. It will regain its primary path from R1 to R2.

show ip route static

That was our IP SLA configuration lab.

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