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### Understand the alert
This `ping_host_reachable` alert checks the network reachability status of a specific host. When you receive this alert, it means that the host is either `up` (reachable) or `down` (unreachable).
### What is network reachability?
Network reachability refers to the ability of a particular host to communicate with other devices or systems within a network. In this alert, the reachability is monitored using the `ping` command, which sends packets to the host and checks for the response. The alert evaluates the packet loss percentage over a 30-second period.
### Troubleshoot the alert
1. Verify if the alert is accurate: Check if there are transient network issues or if there is a problem with the particular host. You can run the `ping` command manually to see if the packet loss percentage is consistent over time.
```
ping -c 10 <host IP or domain>
```
2. Check the network connectivity: Ensure there are no issues with the local network or the physical connections (switches, routers, etc.). Look for potential network bottlenecks, high traffic, and hardware failures that can affect reachability.
3. Check the host's health: If the host is reachable, log in to the system and examine its performance, stability, and resource usage. Look for indicators of high system load, resource constraints, or unresponsive processes.
4. Examine network security policies and firewalls: Network reachability can be affected by misconfigured firewalls or security policies. Ensure there are no restrictions blocking the communication between the monitoring system and the host.
5. Analyze logs for any relevant information: Check system logs (e.g., `/var/log/syslog`) and application logs on both the monitoring system and the target host. Look for error messages, timeouts, or connectivity problems.
### Useful resources
1. [Understanding High Packet Loss in Networking](https://www.fiberplex.com/blog/understanding-high-packet-loss-in-networking)
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