How To Identify Operating System Using TTL Value And Ping Command

Did you know that we can identify which operating system is running on a remote system by simply pinging it? Yes! In this brief guide, we will see how to determine operating system with TTL value and Ping command. This method should work on any operating system that has Ping command line utility installed.

There are plenty of commands, applications, and utilities exists to find type of the OS of a remote system. However, finding operating system type with TTL is super easy!

You can quickly detect whether a system is running with Linux, or Windows or any other OS by looking at the TTL value from the output of the ping command. You don't need any extra applications to detect a remote system's OS.

What is TTL?

In the context of networking, TTL or "Time to Live" is a mechanism that limits the lifespan of data on a network. It’s a value that determines how long data should be kept before being discarded. 

It's used in two main ways:

1. IP Packets: Each IP packet has a TTL field, which is an 8-bit value. As the packet traverses through routers, the TTL value is decremented by 1 each time it passes a router. If the TTL reaches zero before the packet reaches its destination, the packet is discarded. This prevents packets from circulating indefinitely on the network.
2. DNS Records: TTL values in DNS records indicate how long a resolver should cache the DNS query before the information needs to be refreshed. A lower TTL means the DNS information is updated more frequently, while a higher TTL can improve DNS resolution times but may lead to outdated information being used if changes occur.

In both cases, TTL helps manage network resources efficiently and ensures data does not persist longer than necessary.

What is Ping Command?

The Ping command is a network utility that tests the reachability of a host on an Internet Protocol (IP) network and measures the round-trip time for messages sent from the originating host to a destination computer. The name "Ping" comes from the sound of the sonar echo as it detects another ship in the ocean.

Here's how it works:

1. Initiation: You issue the Ping command along with a specific URL or IP address.
2. Transmission: Your computer sends a series of packets of information to that device.
3. Response: It then waits for a response from the target host.
4. Results: When the response is received, the Ping tool shows how long each packet took to make the round trip.

Ping uses the Internet Control Message Protocol (ICMP) to send echo request messages and waits for a reply. It's a fundamental tool used to troubleshoot connectivity issues and check the status of the network connection between two hosts.

TTL Values

The TTL value varies depends on the version of an operating system and device.

The default initial TTL value for Linux/Unix is 64, and TTL value for Windows is 128.

Here is the default initial TTL values for popular operating systems such as Linux, FreeBSD, Mac OS, Solaris and Windows.

You can view the complete list of TTL values for different operating systems and devices at the end.

Detect remote host's operating system with TTL value

As I already stated, TTL, stands for Time to live, is a timer value included in packets sent over TCP/IP-based networks that tells the recipients how long to hold or use the packet or any of its included data before expiring and discarding the packet or data.

And the Ping command is used to check the connectivity and reachability of system or device on local area network or wide area network. Ping command comes pre-installed in most operating systems.

To view the TTL value of a Linux/Windows host, simply ping the host from itself or from other systems on the network:

Example:

$ ping -c5 localhost

Sample output from my Fedora desktop:

PING localhost(localhost (::1)) 56 data bytes
64 bytes from localhost (::1): icmp_seq=1 ttl=64 time=0.063 ms
64 bytes from localhost (::1): icmp_seq=2 ttl=64 time=0.057 ms
64 bytes from localhost (::1): icmp_seq=3 ttl=64 time=0.070 ms
64 bytes from localhost (::1): icmp_seq=4 ttl=64 time=0.067 ms
64 bytes from localhost (::1): icmp_seq=5 ttl=64 time=0.056 ms

--- localhost ping statistics ---
5 packets transmitted, 5 received, 0% packet loss, time 4096ms
rtt min/avg/max/mdev = 0.056/0.062/0.070/0.005 ms

As you can see, I get 64 as TTL value in the above output. Because it is a Linux system.

What about the Windows hosts? Let us see what we get if we ping a Windows system.

I am going to ping the Windows 10 desktop from my Fedora desktop. The IP address of My Windows 10 is 192.168.122.239.

$ ping -c5 192.168.122.239

Sample output:

PING 192.168.122.239 (192.168.122.239) 56(84) bytes of data.
64 bytes from 192.168.122.239: icmp_seq=1 ttl=128 time=6.85 ms
64 bytes from 192.168.122.239: icmp_seq=2 ttl=128 time=0.510 ms
64 bytes from 192.168.122.239: icmp_seq=3 ttl=128 time=0.601 ms
64 bytes from 192.168.122.239: icmp_seq=4 ttl=128 time=0.541 ms
64 bytes from 192.168.122.239: icmp_seq=5 ttl=128 time=0.558 ms

--- 192.168.122.239 ping statistics ---
5 packets transmitted, 5 received, 0% packet loss, time 4088ms
rtt min/avg/max/mdev = 0.510/1.812/6.851/2.519 ms

Note the the TTL value? It is 128. The default TTL value for Windows OS is 128.

Initial TTL values

The following table shows the default Initial TTL values of various operating systems and devices.

Infographic

Conclusion

This method may not be accurate all the time. However, it will give an idea of the underlying operating system in a remote system. If you know only the IP address of a remote system, you can use the Ping command to get the name or type of the OS.

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