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Monitoring as Code: Learn more about the ICMP Monitor Construct.

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What are ICMP Monitors?

ICMP monitors verify that a host is reachable and responding. Typical use cases include:
  • Detecting network-level outages before they’re visible via HTTP endpoints
  • Monitoring latency across regions to identify geographic performance issues
  • Verifying reachability for servers, load balancers, or network appliances that don’t expose HTTP endpoints or open TCP ports
  • Tracking packet loss to catch network quality degradation early

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How do ICMP monitors work?

ICMP monitors perform ping tests:
  • Hostname resolution: If a hostname is provided, Checkly resolves it to an IP address.
  • Ping execution: Multiple ICMP Echo Request packets (configurable from 1–50, default: 10) are sent from your configured location(s).
  • Response valildation: ICMP Echo Reply packets are received. Round-trip latency and packet loss are measured and evaluated against your configured assertions.
For example, pinging checklyhq.com with 10 pings returns: 
{
  "latency": {
    "min": 12.3,
    "max": 18.7,
    "avg": 14.2,
    "stddev": 2.1
  },
  "packetLoss": 0,
  "timingPhases": { "dns": 5.2 },
  "pingsSucceeded": 10,
  "pingsFailed": 0
}
The response appears on the results page as both raw output and parsed JSON. You can use it as a reference to define assertions for expected values.

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Troubleshooting Common Issues

Symptom: ICMP monitor shows complete packet loss, but the website/API works fineRoot cause:
  • Firewall rules blocking ICMP: Many organizations block ICMP echo request packets at the firewall, load balancer, or host level as a security measure
How to detect and fix:
  1. Verify HTTP connectivity: Create an API or URL monitor for the same hostname to confirm it’s reachable
  2. Check both protocols: Test both IPv4 and IPv6, some hosts allow ICMP on one protocol but not the other
  3. Confirm with infrastructure team: Ask if ICMP is intentionally blocked in security policies
When to use a different monitor type: If ICMP is deliberately blocked, use TCP, URL, or API checks instead to verify availability at the application layer.
Symptom: ICMP monitor shows high latency or packet loss from certain locations but not othersRoot causes:
  • Geographic routing: Network paths vary by region, some routes may be congested
  • Transit provider issues: Problems with specific ISPs or peering connections
  • Rate limiting: Some hosts rate-limit ICMP responses, affecting distant locations more
How to detect and fix:
  1. Compare across locations: Run monitors from multiple regions to identify which paths are affected
  2. Monitor trends over time: Check if issues are persistent or intermittent
  3. Cross-reference with other monitor types: Compare ICMP latency with TCP/HTTP latency from the same locations
  4. Use latency assertions: Set region-specific assertions, e.g., latency.avg less than 50ms for nearby regions, 200ms for distant ones
Investigation tip: Persistent high latency from a specific region often indicates routing issues with your hosting provider or CDN configuration.