ping 中的“TTL"是什么意思

 

简单来说就是表示一个数据包在网络中可以跳跃的结点数据，当该数据为零时本数据包将被抛弃

详细解释看以下引用：

TTL (although named as "time" to live) is actually refering to the number of hops a packet can go thru before it "dies" off. How? Why? 
　　Well, let's go back to some basics (help me out if I am wrong here okay?)
- data is sent thru the internet in form of packets (ie small packages/group of bits collected in the binary form)
- besides the data, there are many more other information that is packed into the same package (for many purposes like indification, 
　　error correction, etc and also the TTL info)
- a packet will travel thru the networks to go from the sender to reach the destination using any connections of the network, it will
   go thru lots of connection points (routers or hops) and it will keep on traveling (even though in loops) thru-out this network until 
   it reaches its destination
- just imagine lots of packets traveling in loops in a certain network but never manages to reach its destination... well, they will 
　　keep on going around in the network to try to reach the destination... basically the network will be congested!
- so to ensure that a data will not "live" forever to clogg the network, the TTL is introduced. It is a backward counter (basically a 
　　number) and will start from a value assigned by (probably) the sender's computer system and this number will be decremented by one 
　　whenever it reaches a hop until the value of TTL equals to zero (which means it will die off  ) where the packet will be discarded by 
　　the router (hop).
- TTL is a small (8-bits) data that is being attached at the end of this package (I think it is 8-bit, therefore "255")

- so strictly speaking TTL refers to the number of hops a packet can make before it will be discarded; but of course, indirectly, it 
　　also shows you the "time" of how long a packet's life is left.

- when you ping TTL=243 it means that the data had traveled 12 hops that's it... (if the initial is set to 255 of course, and in this 
　　case, I think so)
- a packet does not contain any timing information as far as I know...
- the way of knowing how fast a server connection is has been given by the time=323ms

My guess is:
- a high starting/initial TTL number would indicate that a packet is important/ it might need to travel far (many hops) ?? Am I right?
- a high TTL number you see when you ping shows that the data only needs to travel less hops to reach it's destination from YOUR computer