📘CCNP Enterprise – ENARSI (300-410)
IP SLA (Internet Protocol Service Level Agreement) is a Cisco feature that measures network performance by sending test traffic across a network. It allows network engineers to monitor things like delay, jitter, and connectivity, so they can quickly detect and troubleshoot performance problems.
Think of IP SLA as a network health monitor that continuously tests the performance of your network and tells you where issues exist before users even notice.
1. What IP SLA Can Measure
IP SLA can measure several key network performance metrics:
- Delay / Latency
- Definition: How long it takes for packets to travel from one device to another.
- Why it matters: High delay can affect applications like VoIP, video conferencing, or remote servers.
- IP SLA example: You can configure an IP SLA operation to measure the round-trip time (RTT) to a remote router.
- Jitter
- Definition: The variation in packet delay over time.
- Why it matters: Applications like voice or video are sensitive to jitter because inconsistent packet arrival can cause poor call quality or video buffering.
- IP SLA example: IP SLA can measure jitter by sending UDP packets at regular intervals to see how consistent the delay is.
- Connectivity
- Definition: Whether a device is reachable or not.
- Why it matters: Detects if a network path is down or intermittent.
- IP SLA example: ICMP echo (ping) operations can verify connectivity to critical servers, routers, or remote sites.
- Packet Loss
- Definition: The percentage of packets that are lost in transit.
- Why it matters: Packet loss can disrupt applications and indicate congestion or faulty links.
- Tracking Objects
- Definition: IP SLA can create “objects” that track SLA results and can trigger actions if thresholds are exceeded.
- Why it matters: You can automate network responses when performance drops below acceptable levels (like rerouting traffic).
2. How IP SLA Works
Here’s the step-by-step explanation in simple terms:
- Configure an IP SLA operation
- Example: Measure RTT to a server every 10 seconds.
- Activate the operation
- Start sending test packets across the network.
- Monitor performance metrics
- The router stores results such as delay, jitter, and packet loss.
- Create a tracking object
- Associate IP SLA results with a “track” object.
- Example: If RTT exceeds 200 ms, mark the path as down.
- Take action
- Use routing protocols (like EIGRP or OSPF) to switch traffic to backup links automatically when IP SLA indicates failure.
3. IP SLA Operations Relevant for the Exam
Some IP SLA operations you must know:
| Operation | Measures | Exam relevance |
|---|---|---|
| ICMP Echo | Connectivity, RTT | Ping test to check if a device is reachable |
| UDP Jitter | Jitter, delay, packet loss | VoIP and video performance monitoring |
| TCP Connect | Connectivity, delay | Checks if a TCP session can be established |
| HTTP / HTTPS | Response time | Measures application server performance |
| DNS | Response time | Check if DNS queries are performing correctly |
| ICMP Path Echo | Delay and route measurement | Trace multiple hops to detect slow links |
For ENARSI, focus on ICMP Echo, UDP Jitter, TCP Connect, and tracking objects, as these are commonly used in troubleshooting scenarios.
4. Tracking Objects
IP SLA works well with tracking objects, which are like network sensors that monitor performance thresholds.
- Step 1: Define an IP SLA operation
- Step 2: Create a track object linked to the SLA
- Step 3: Set thresholds
- Example: Track the SLA and mark the route down if RTT > 100 ms or packet loss > 2%.
- Step 4: Use the track object in routing
- Example: In a floating static route, make it active only if the SLA track object is up.
Commands Example:
! Configure IP SLA operation
ip sla 1
icmp-echo 192.168.1.1
frequency 10
ip sla schedule 1 life forever start-time now
! Create a tracking object
track 1 ip sla 1 reachability
delay up 10 down 5
! Use in static route
ip route 10.1.1.0 255.255.255.0 192.168.1.2 track 1
5. Using IP SLA to Troubleshoot Network Performance
IP SLA is very practical for real IT troubleshooting:
- Detecting slow links
- Measure RTT across WAN links.
- Identify which link is slower than expected.
- Monitoring VoIP quality
- Use UDP Jitter to see if voice packets experience delay or variation.
- Helps troubleshoot call quality issues.
- Automated failover
- IP SLA tracking objects can signal routing protocols to reroute traffic if a link is underperforming.
- Proactive alerting
- Continuously measure network performance to detect degradation before users complain.
6. IP SLA for the Exam: Key Points
- IP SLA measures network performance, not just connectivity.
- Know the main metrics: delay, jitter, packet loss, connectivity.
- Understand tracking objects and how they integrate with routing protocols.
- Be able to interpret SLA results:
- High RTT → network latency
- High jitter → inconsistent packet delivery
- Unreachable → connectivity problem
- Focus on ICMP Echo, UDP Jitter, TCP Connect operations.
- IP SLA can be scheduled to run continuously or at intervals.
7. Example Scenario for IT Environment
Imagine a company has two WAN links to a remote office. Users complain about slow file transfers and choppy video calls.
- Configure IP SLA UDP Jitter to monitor VoIP traffic on both links.
- Create tracking objects linked to IP SLA results.
- Configure floating static routes that automatically switch traffic to the better-performing link when IP SLA detects high delay or jitter.
This way, network performance issues are automatically detected and mitigated without manual intervention.
✅ Summary
IP SLA is a powerful tool for:
- Monitoring connectivity, delay, jitter, and packet loss
- Creating tracking objects to integrate with routing
- Proactively troubleshooting network performance issues
- Enabling automated failover and performance-aware routing
For the ENARSI exam, focus on:
- Configuring IP SLA operations
- Interpreting results
- Using tracking objects
- Understanding delay, jitter, and connectivity concepts
