4.4 Configure and verify IPSLA

What this objective tests

IP Service Level Agreement (IP SLA) lets a Cisco device test the network on purpose. It sends synthetic probes, records statistics, and feeds object tracking. The exam tests the operation, the schedule, and the track object that lets routing react.

The three parts

Operation = which probe to send (icmp-echo, udp-jitter, ...)
Schedule  = when to run it
Tracking  = optional object that turns the result into up/down state

An operation without a schedule never runs. A measurement without tracking changes nothing.

ICMP echo operation

This operation sends ping-like probes every 5 seconds to 10.10.20.1:

conf t
ip sla 10
 icmp-echo 10.10.20.1 source-interface Loopback0
 frequency 5
ip sla schedule 10 life forever start-time now
end

• frequency 5 sends one probe every 5 seconds.
• life forever start-time now starts the operation at once and runs it forever.

Verify:

show ip sla configuration 10
show ip sla statistics 10

Expected output from show ip sla statistics 10:

IPSLAs Latest Operation Statistics

IPSLA operation id: 10

        Latest RTT: 4 milliseconds
Latest operation start time: 12:15:04 UTC Sun Jul 19 2026
Latest operation return code: OK
Number of successes: 44
Number of failures: 0
Operation time to live: Forever

Read the return code first. OK means the probe worked. Timeout means no reply. Then compare successes to failures.

Track a static route

IP SLA becomes useful when a track object turns probe results into routing decisions. Scenario: R1 has two internet providers. Use ISP1 as primary. Fail over to ISP2 when the probe to ISP1 fails.

conf t
ip sla 10
 icmp-echo 198.51.100.1 source-interface GigabitEthernet0/0
 frequency 5
ip sla schedule 10 life forever start-time now
!
track 10 ip sla 10 reachability
 delay down 10 up 5
!
ip route 0.0.0.0 0.0.0.0 198.51.100.1 track 10
ip route 0.0.0.0 0.0.0.0 203.0.113.1 250
end

This configuration says:

• The primary default route exists only while track object 10 is up.
• Track object 10 follows the reachability of IP SLA operation 10.
• If the probe fails for 10 seconds, the track goes down and the primary route is removed.
• The floating static route with administrative distance 250 becomes the backup.
• delay down 10 up 5 dampens flapping. One bad probe does not churn the route.

Verify:

show track 10
show ip route 0.0.0.0

Expected output while ISP1 is healthy:

Track 10
  IP SLA 10 reachability
  Reachability is Up
    5 changes, last change 00:22:14

S* 0.0.0.0/0 [1/0] via 198.51.100.1

Track an HSRP gateway

The same track object can control Hot Standby Router Protocol (HSRP) priority. When the uplink fails, the standby router takes over the gateway.

interface GigabitEthernet0/1
 ip address 10.10.10.2 255.255.255.0
 standby 1 ip 10.10.10.1
 standby 1 priority 110
 standby 1 preempt
 standby 1 track 10 decrement 20

While track 10 is up, R1 has priority 110 and stays active. When track 10 goes down, the priority drops to 90. The standby router with priority 100 preempts and becomes active.

Lab: static route failover with IP SLA

Topology:

+-- ISP1 198.51.100.1/30 (Gi0/0, .2 on R1)
   LAN -- R1 -+
              +-- ISP2 203.0.113.1/30 (Gi0/1, .2 on R1)

Goal: use ISP1 as the primary default route. Fail over to ISP2 when the probe to 198.51.100.1 fails.

Do these steps:

1. Configure Gi0/0 with 198.51.100.2/30 and Gi0/1 with 203.0.113.2/30.
2. Create IP SLA operation 10: icmp-echo 198.51.100.1 source-interface GigabitEthernet0/0 with frequency 5.
3. Schedule it: ip sla schedule 10 life forever start-time now.
4. Create the track object: track 10 ip sla 10 reachability with delay down 10 up 5.
5. Add the primary route: ip route 0.0.0.0 0.0.0.0 198.51.100.1 track 10.
6. Add the backup route: ip route 0.0.0.0 0.0.0.0 203.0.113.1 250.
7. Verify before failure: show ip sla statistics 10 shows successes, show track 10 shows Up, show ip route 0.0.0.0 shows the ISP1 route.
8. Shut the ISP1 next-hop interface in the lab to simulate failure.
9. Verify after failure: show track 10 shows Down and show ip route 0.0.0.0 shows S* 0.0.0.0/0 [250/0] via 203.0.113.1.
10. Restore ISP1. Confirm the primary route returns after the delay up timer.

Full device configuration:

conf t
interface GigabitEthernet0/0
 description ISP1
 ip address 198.51.100.2 255.255.255.252
!
interface GigabitEthernet0/1
 description ISP2
 ip address 203.0.113.2 255.255.255.252
!
ip sla 10
 icmp-echo 198.51.100.1 source-interface GigabitEthernet0/0
 frequency 5
ip sla schedule 10 life forever start-time now
!
track 10 ip sla 10 reachability
 delay down 10 up 5
!
ip route 0.0.0.0 0.0.0.0 198.51.100.1 track 10
ip route 0.0.0.0 0.0.0.0 203.0.113.1 250
end

Expected result: failover takes about 10 seconds (the delay down timer). Failback takes about 5 seconds (the delay up timer).

Exam traps

• An IP SLA operation without ip sla schedule ... start-time now never runs. No statistics means no schedule, not no problem.
• Probing a next-hop that answers while the path beyond it is broken keeps the track up and the broken route installed. Probe a target that proves the path you care about.
• The backup static route needs a worse administrative distance like 250. Two equal-distance defaults load-share; they do not fail over.
• delay down 10 up 5 is flap dampening. Do not expect instant failover while a delay timer is configured.
• show ip sla configuration shows intent. show ip sla statistics and show track show what happened. Verify with the second pair.
• UDP jitter needs ip sla responder on the destination device. ICMP echo does not.

Pass check

You are ready when you can do these things:

• Configure an ICMP echo operation with a schedule that runs forever.
• Connect an operation to a track object and a tracked static route.
• Configure HSRP tracking with a priority decrement.
• Read show ip sla statistics and show track and say if failover should happen.