What's the TTL?

What do you mean by a TTL?

The TTL is the value of an IP protocol that tells the network whether the packet's time in the network is too long and should be discarded. There are a number of reasons why the package cannot be delivered to the destination for a certain amount of time.

The initial value of the TTL is usually the system default, which is a 8-bit field in the header. The first idea of the TTL is to determine a time range that discards the package over that time. Because each router has at least one less TTL domain, the TTL usually represents the maximum number of routers that the packet can pass before being discarded. When the count to 0 o'clock, the router decides to discard the packet and send an ICMP message to the original sender.

Second, the TTL return value in ping

For example, I ping a worry-free web site, click "Start Menu-run", in the Run input box to enter the cmd command, and then execute the command to open a command prompt to run the window, and then enter the "Ping www.xue51.com" command (except double quotes), input will return the TTL value. As shown in the figure:

Above the degree of loss is 0%, indicating that the URL can be normal access to open, if found unacceptable, the data are all lost, that means that the server space in addition to the problem, this will contact your space service provider.

TTL value by default, the TTL value of the Linux system is 64 or 255,windows NT/2000/XP system's default TTL value is the TTL value of the 128,win7 system is the 64,windows 98 system TTL value is 32, The UNIX host has a TTL value of 255. (This was found on the web), the purpose of the dawning blog is to use the FreeBSD system (may have been replaced), where the TTL value may be 64, rather than the UNIX host 255, so from here to the destination host through 64-51 = 13 routes (here easily cause misunderstanding, 64 is the default TTL for Fressbsd or initiator TTL, this TTL initial value should be ping side, I think it should be the TTL on behalf of the initiator, because the TTL is set by the sending host.

Three, TTL value reference:

The longer the TTL time, the longer the cache time, the more difficult the update will be effective in time. Increase the TTL value to save the domain name resolution time, to speed up the site access.

The TTL setting is smaller, and the effective time is faster. Two. Reduce the TTL value and reduce the inaccessible time when changing space. On the TTL value of the network words also have TT love, the plain lesbian, when these are the digression