ping

What does ping do?

At its core, ping sends Internet Control Message Protocol (ICMP) echo requests to a specified host and waits for an ICMP echo reply. This process allows you to verify if a host is reachable and measure the round-trip time (RTT) – the time it takes for a packet to travel to the host and back. Successful responses indicate that the host is online and reachable, while failures suggest potential network problems.

Basic ping Usage

The simplest form of the ping command is:

ping <hostname or IP address>

For example, to ping Google’s public DNS server:

ping 8.8.8.8

This will send packets continuously until you manually interrupt it (usually with Ctrl+C). The output shows various metrics including:

• packet transmit/receive: The number of packets sent and received.
• packet loss: Percentage of packets not received.
• time (ms): Round-trip time in milliseconds.

Specifying the Number of Pings

To send a specific number of pings, use the -c option:

ping -c 5 8.8.8.8

This will send 5 packets and then stop. Useful for quick checks.

Controlling Packet Size

The -s option allows you to specify the size of the ICMP echo request packet in bytes:

ping -s 1000 8.8.8.8

This sends packets of 1000 bytes, helping you test for Maximum Transmission Unit (MTU) issues.

Verbose Output with -v

For more detailed information, including timestamps, use the -v (verbose) option:

ping -v 8.8.8.8

This provides a more granular view of each packet’s journey.

Timing Parameters: -i and -W

• -i <interval>: Sets the interval (in seconds) between each ping. Useful for monitoring network stability over time. For example: ping -i 1 8.8.8.8 sends a ping every second.

• -W <timeout>: Sets the timeout (in seconds) before ping declares a packet lost.

ping -i 2 -W 5 8.8.8.8

This example pings every 2 seconds and waits 5 seconds for a response before timing out.

Pinging a Hostname

Replace the IP address with a hostname:

ping google.com

This will resolve the hostname to its IP address and then send ICMP echo requests.

Troubleshooting Network Connectivity

If ping fails to reach a host, it indicates a potential problem somewhere along the network path. The error messages provide clues; for example, a “Destination Host Unreachable” message suggests a routing issue, while “Request timeout” might point to network congestion or a firewall problem.

ping6 for IPv6

For IPv6 addresses, use the ping6 command. The options are largely the same:

ping6 2001:4860:4860::8888

This pings an IPv6 address.

This guide covers the core functionalities of the ping command. Experiment with different options to understand its capabilities better and use it for effective network troubleshooting.