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This article mainly explains "what is ping, time,TTL". The content in the article is simple and clear, and it is easy to learn and understand. Please follow the editor's train of thought to study and learn "what is ping, time,TTL".

First, what is ping?

PING (Packet Internet Grope), an Internet packet explorer, is a program used to test the number of network connections. Ping sends an ICMP echo request message to the destination and reports whether it has received the desired ICMP echo reply. How does he work? look at the picture below.

Ping request description

Second, what is TTl?

TTL: time to Live

Specifies the number of network segments allowed before the packet is discarded by the router.

The TTL is set by the sending host to prevent packets from looping endlessly over the IP Internet. When forwarding IP packets, the router is required to reduce the TTL by at least 1.

The types of ICMP messages involved when using PING:

One request echo for ICMR (ICMP Echo Request)

One echo reply for ICMP (ICMP Echo Reply)

The TTL field value can help us identify the operating system type.

The TTL field value of ICMP echo reply for UNIX and UNIX-like operating systems is 255,

The TTL field value for Compaq Tru 5.0ICMP echo reply is

The TTL field value of Microsoft Windows NT/2K operating system ICMP echo reply is 128,

The TTL field value of Microsoft Windows 95 operating system ICMP echo reply is 32.

Of course, the TTL value returned is the same

But in some cases, it's special.

The TTL field value of LINUX Kernel 2.2.x & 2.4.x ICMP echo reply is

FreeBSD 4.1, 4.0, 3.4

Sun Solaris 2.5.1, 2.6, 2.7, 2.8

OpenBSD 2.6, 2.7

NetBSD

HP UX 10.20

The TTL field value of ICMP echo reply is 255,

Windows 95/98/98SE

Windows ME

The TTL field value of ICMP echo reply is 32

Windows NT4 WRKS

Windows NT4 Server

Windows 2000

Windows XP

The TTL field value of ICMP echo reply is 128,

In this way, we can identify the operating system in this way.

Third, give examples.

C:\ Documents and Settings > ping blog.51yip.comPinging blog.51yip.com [173.201.152.6] with 32 bytes of data:Reply from 173.201.152.6: bytes=32 time=257ms TTL=45Reply from 173.201.152.6: bytes=32 time=256ms TTL=45Reply from 173.201.152.6: bytes=32 time=262ms TTL=45Reply from 173.201.152.6: bytes=32 time=258ms TTL=45Ping statistics for 173.201.152.6:Packets: Sent = 4, Received = 4, Lost = 0 (0 loss), Approximate round trip times in milli-seconds:Minimum = 256ms, Maximum = 262ms, Average = 258ms

From this, we can conclude that blog.51yip.com is a linux host and arrives at the local machine after-45 to 19 transfers, time=257ms. This time is the time of a request. The smaller the time, the faster the speed, the greater the speed, the slower the speed.

C:\ Documents and Settings > ping 127.0.0.1Pinging 127.0.0.1 with 32 bytes of data:Reply from 127.0.0.1: bytes=32 time

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