In networking, ping is a diagnostic tool that checks whether one device can reach another across an IP network. It uses the ICMP (Internet Control Message Protocol) to send small packets called echo requests to a target host, and if the host is reachable, it responds with echo replies.

Connectivity Test → Confirms if two devices can communicate.

Latency Measurement → Shows round-trip time (RTT), i.e., how long packets take to travel there and back.

Packet Loss Detection → Reveals if some requests don’t get replies, indicating possible network issues.

Example

ping 8.8.8.8

Output might look like:

Reply from 8.8.8.8: bytes=32 time=20ms TTL=117
Reply from 8.8.8.8: bytes=32 time=21ms TTL=117

• Checking if a server or website is reachable.

• Troubleshooting network problems (is the issue local or remote?).

• Measuring network performance and delay.

• Some networks or servers block ping for security reasons, so a failed ping doesn’t always mean the host is down.

• Ping only tests ICMP connectivity, not whether specific services (like HTTP or SSH) are available.

In Oracle Cloud Infrastructure (OCI), Telnet is mainly used as a troubleshooting tool to verify whether a specific TCP port on a compute instance or service is reachable. It’s not used for secure remote login (SSH is the standard), but rather to confirm connectivity and diagnose issues with VCN security lists, network security groups (NSGs), or firewalls.

• Protocol: Telnet operates over TCP and lets you attempt a connection to a host and port.

• Check if a port (e.g., 22 for SSH, 80 for HTTP, 443 for HTTPS) is open and accessible between instances.

• Troubleshoot blocked traffic due to misconfigured VCN Security Lists, NSG rules, or instance firewalls.

Usage

telnet <target_IP> <port>

Example

telnet 10.0.0.5 22

1. Install Telnet on your compute instance (e.g., yum install telnet )

2. Run Telnet to the target instance’s IP and port.

3. If connection fails:

• Check VCN Security List ingress rules (ensure TCP traffic on the port is allowed).

• Verify NSG rules if applied.

• Confirm firewall settings inside the instance.

4. If connection succeeds: The port is open and reachable, meaning the issue lies elsewhere (e.g., application misconfiguration).