01 April 2010

IP packet contains n number of information within. One important protocol is TTL i.e. Time To Live.
It is an eight-bit field helps prevent datagrams from persisting (e.g. going in circles) on an internet. This field limits a datagram's lifetime. It is specified in seconds, but time intervals less than 1 second are rounded up to 1. In latencies typical in practice, it has come to be a hop count field. Each packet switch (or router) that a datagram crosses decrements the TTL field by one. When the TTL field hits zero, the packet is no longer forwarded by a packet switch and is discarded. Typically, an ICMP message is sent back to the sender that it has been discarded.
In addition to that there is a good reason to use this field, i.e. for identifying the other end PC, device or OS.
How? Lets check:
goto command prompt (in linux goto terminal)
and use ping command to identify the availability of other end device.
You will find :
Here you can see the TTL (highlighted) value is 30 the end pc or device or os is windows NT machine. Its range could be 28 to 32. Similarly for linux machine (open source machines) it would be 62-64, for windows (windows machines) 126-128. For routers it would be 255-256.
You can also check this with following list.

OS/Device Version Protocol TTL value
AIX 3.2, 4.1 ICMP 255
BSDI BSD/OS 3.1 and 4.0 ICMP 255
Cisco ICMP 254
HP-UX ICMP 255
HP-UX TCP 64
Juniper ICMP 64
Linux 2.0.x kernel ICMP 64
Linux 2.2.14 kernel ICMP 255
Linux 2.4 kernel ICMP 255
Linux Red Hat 9 ICMP and TCP 64
NetBSD ICMP 255
Solaris 2.5.1, 2.6, 2.7, 2.8 ICMP/TCP 255/64
SunOS 5.7 ICMP and TCP 255
Windows for Workgroups TCP and UDP 32
Windows 95 TCP and UDP 32
Windows 98 ICMP/TCP 128
Windows NT 4.0 TCP and UDP 128
Windows Server 2003 128
Windows XP ICMP/TCP/UDP 128

1 comment:

  1. PC has different issue related to different software installed in it. Operating system is as important for the user and its main advantages are often explained very well to rush my essay through a person may judge the real uses of PC but PC is nothing without operating system as OS is like its important part required to be executed. Software matters a lot for hardware.

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