Til value in Ping Command

TTL indicates the time to live, that is, the amount of time the ping packet can have on the network. When we Ping hosts on the network, a data packet is sent from the local machine to the destination host through a certain number of routers. However, for many reasons, some data packets cannot be transmitted to the target host normally. If these data packets are not sent for a long time, the data packets will be transmitted over the network, increasing the network overhead. After a data packet is transmitted to a vro, TTL is automatically reduced by 1. If the data packet is reduced to 0 but not transmitted to the target host, the data packet is automatically lost. As the third time when I ping Shuguang's blog above, the request timed out occurs and the TTL is increased to reduce the consumption of network resources. By default, the TTL value of Linux is 64 or 255, the TTL value of Windows NT/2000/XP is 128, and the TTL value of Windows 98 is 32, the TTL value of a unix host is 255. (This is found on the network). The target host of Shuguang blog uses the FreeBSD system. The TTL value may be 64, instead of 255 of the UNIX host, therefore, from me to the target host, the host goes through 64-51 = 13 routes. When we do not know the operating system of the target host, we can guess based on TTL, but it is not necessarily 100% accurate. If the target host is windows, but after 75 routers, the TTL returned value is 128-75 = 53. Therefore, you may think that the target host is a Linux system, but generally does not pass through so many routers, therefore, TTL is used to determine the operating system of the target host. By default, the TTL value of Linux is 64 or 255, the TTL value of Windows NT/2000/XP is 128, and the TTL value of Windows 98 is 32, the TTL value of a unix host is 255.

 

TTL does not determine the number of routes from the source address to the destination address. It is only a set time, but a set value. the TTL value you ping is only the set value. The default value is 128 for Windows instances, and 64 for Linux instances. This can also be changed. For example, if my WINXP changes the TTL to 64, it can also cheat some cainiao hackers to make him think that I am a Linux system. each time a route exists, TTL is reduced by 1. Therefore, TTL settings are too long. It takes a long time to access a website that does not exist before "cannot be opened" is displayed ", because he tried many paths. If the TTL is set too small, some websites with poor networks that need to bypass some routes may not be opened. However, this is not possible. There are very few target addresses and more than 32 routes are required.