I am just learning about OS fingerprinting, when i ping a certain ip address, it gives me a ttl value of 56.
What is an operating system with a value of 56? I only know about the popular operating system's ttl value such as; 128 for windows xp, 64 for freeBSD, linux kernel between 2.4 and 2.6, etc
Please note that the TTL decreases every time it passes a networking device(e.g. router) as stated in RFC 791
The time to live is set by the sender to the maximum time the
datagram is allowed to be in the internet system. If the datagram
is in the internet system longer than the time to live, then the
datagram must be destroyed.
This field must be decreased at each point that the internet header
is processed to reflect the time spent processing the datagram.
Even if no local information is available on the time actually
spent, the field must be decremented by 1. The time is measured in
units of seconds (i.e. the value 1 means one second). Thus, the
maximum time to live is 255 seconds or 4.25 minutes. Since every
module that processes a datagram must decrease the TTL by at least
one even if it process the datagram in less than a second, the TTL
must be thought of only as an upper bound on the time a datagram may
exist. The intention is to cause undeliverable datagrams to be
discarded, and to bound the maximum datagram lifetime.
Some higher level reliable connection protocols are based on
assumptions that old duplicate datagrams will not arrive after a
certain time elapses. The TTL is a way for such protocols to have
an assurance that their assumption is met.
Also, TTL can be easily spoofed by changing registry in Windows and by using iptables in Linux, so there are a lot of possibilites and nobody can say it for sure.
