IP SLA

R1(config)# ip sla 1
R1(config-ip-sla)# http get http://172.16.55.87/
R1(config-ip-sla-http)# frequency 60
R1(config-ip-sla-http)# timeout 5000

The above configuration creates a monitor which sends an HTTP GET request to the specified URL every 60 seconds and checks for a valid response. The timeout has been set for 5000 milliseconds, or 5 seconds. Note that this configuration only checks for HTTP connectivity to the proxy itself;

For HTTP connectivity to external sites through the proxy

R1(config-ip-sla)# http get http://external-site/ proxy http://172.16.55.87/  name-server 172.16.44.10




Timeout is the maximum time required for SLA operation to complete - for example the timeout waiting for probe response. Threshold is boundary value measured ove the operation RESULT (e.g. RTT, or jitter value collected during the opearation). Crossing threshold usually means SLA contract violation. Note that these two values apply to DIFFERENT objects.

Timeout is directly used to restart the operation. Threshold is used to activate a response to IP SLA violation, e.g. send SNMP trap or start seconday SLA operation.

You should configure the sla based on Frequency > Timeout > Threshold.

If you configure Timeout > Threshold, you can see the RTT and if the RTT exceed Threshold, it is a failure. If you configure Threshold > Timeout, if the RTT exceed timeout but less than Threshold, it won't show the RTT but it is still a failure.
So failure is RTT exceed either Timeout or Threshold.

ip sla monitor 1
type echo protocol ipIcmpEcho 115.0.0.1
timeout 500
threshold 20
frequency 10

Rack1R6#show ip sla monitor statistics
Round trip time (RTT) Index 1
Latest RTT: 36 ms
Latest operation start time: *04:12:47.001 UTC Mon Mar 4 2002
Latest operation return code: Over threshold
Number of successes: 0
Number of failures: 6
Operation time to live: Forever