What is TTL?

[Keefe]

I know it stands for Time to Live...but what does TTL actually mean?

Thanks

[wizbones]

TTL specifies how long a datagram can stay in the internet, it is set by the sender, and is decremented by the routers and hosts who process it.

A datagram will be discarded if the TTL becomes zero and it still hasn't reached its destination. An error message will be sent to the sender.

The original TTL definition uses time in seconds. It can be simplified  by using number of hops, i.e. TTL will be decremented by 1 at each router along the path. Therefore TTL becomes a “hop limit”.

Hope that helps  ;D

[Keefe]

Ahh, thanks man!

That explains the error that says, "TTL expired in transit."

If your an electronic geek you would also recognice it as Transistor, Transistor Logic.  But I doubt if many chips are built with that technology anymore as it is an older form of manufacturing.

[Uranium-235]

ah damn savage I was gonna say dat!

An example of how TTL can be utilized is traceroute. It purposely sets the time to live to zero so an error is reported (TTL is exceeded) at each hop. The SA (Source Address) is read from each packet returned and reports this as a hop along with hop latency. Because each router acts as a “proxy” traceroute will get the message from each router (hop). This is a pretty cool example of how TTL can be used.