linux ping命令

Ping命令一直都在用，但具体详细的使用还不是很了解。下面整理下有关Ping命令的资料。

Ping是潜水艇人员的专用术语，表示回应的声纳脉冲，在网络中Ping 是一个十分好用的TCP/IP工具。它主要的功能是用来检测网络的连通情况和分析网络速度。

Ping的用途就是用来检测网络的连同情况和分析网络速度，但它是通过什么来显示连通呢？这首先要了解Ping的一些参数和返回信息。

以下是PING的一些参数：

[root@centos6 kv]# ping -help
Usage: ping [-LRUbdfnqrvVaA] [-c count] [-i interval] [-w deadline]
            [-p pattern] [-s packetsize] [-t ttl] [-I interface or address]
            [-M mtu discovery hint] [-S sndbuf]
            [ -T timestamp option ] [ -Q tos ] [hop1 ...] destination

Ping的返回信息有Request Timed Out、Destination Net Unreachable和Bad IP address还有Source quench received。

Request Timed Out这个信息表示对方主机可以到达到TIME OUT，这种情况通常是为对方拒绝接收你发给它的数据包造成数据包丢失。大多数的原因可能是对方装有防火墙或已下线。

Destination Net Unreachable这个信息表示对方主机不存在或者没有跟对方建立连接。这里要说明一下destination host unreachable和time out的区别，如果所经过的路由器的路由表中具有到达目标的路由，而目标因为其它原因不可到达，这时候会出现time out，如果路由表中连到达目标的路由都没有，那就会出现destination host unreachable。

Bad IP address 这个信息表示你可能没有连接到DNS服务器所以无法解析这个IP地址，也可能是IP地址不存在。

Source quench received信息比较特殊，它出现的机率很少。它表示对方或中途的服务器繁忙无法回应。

Ping这个命令除了可以检查网络的连通和检测故障以外，还有一个比较有趣的用途，那就是可以利用它的一些返回数据，来估算你跟某台主机之间的速度是多少字节每秒

我们先来看看它有那些返回数据。

Pinging 202.105.136.105 with 32 bytes of data:

Reply from 202.105.136.105: bytes=32 time=590ms TTL=114

Reply from 202.105.136.105: bytes=32 time=590ms TTL=114

Reply from 202.105.136.105: bytes=32 time=590ms TTL=114

Reply from 202.105.136.105: bytes=32 time=601ms TTL=114

Ping statistics for 202.105.136.105:

Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),

Approximate round trip times in milli-seconds:

Minimum = 590ms, Maximum = 601ms, Average = 593ms

在例子中bytes=32表示ICMP报文中有32个字节的测试数据（这是估算速度的关键数据），time=590ms是往返时间。

man ping

PING(8)                System Manager’s Manual: iputils                PING(8)
NAME
       ping, ping6 - send ICMP ECHO_REQUEST to network hosts
SYNOPSIS
       ping [ -LRUbdfnqrvVaAB]  [ -c count]  [ -i interval]  [ -l preload]  [ -p pattern]  [ -s packetsize]  [ -t ttl]  [ -w deadline]  [ -F flowlabel]  [
       -I interface]  [ -M hint]  [ -Q tos]  [ -S sndbuf]  [ -T timestamp option]  [ -W timeout]  [ hop ...]  destination
DESCRIPTION
       ping uses the ICMP protocol’s mandatory ECHO_REQUEST datagram to elicit an ICMP ECHO_RESPONSE from  a  host  or  gateway.   ECHO_REQUEST  datagrams
       (‘‘pings’’) have an IP and ICMP header, followed by a struct timeval and then an arbitrary number of ‘‘pad’’ bytes used to fill out the packet.

OPTIONS
       -a     Audible ping.
       -A     Adaptive ping. Interpacket interval adapts to round-trip time, so that effectively not more than one (or more, if preload is set) unanswered
              probes present in the network. Minimal interval is 200msec for not super-user.  On networks with low rtt this mode is essentially equivalent
              to flood mode.
       -b     Allow pinging a broadcast address.
       -B     Do not allow ping to change source address of probes.  The address is bound to one selected when ping starts.
       -c count
              Stop after sending count ECHO_REQUEST packets. With deadline option, ping waits for count ECHO_REPLY packets, until the timeout expires.
       -d     Set the SO_DEBUG option on the socket being used.  Essentially, this socket option is not used by Linux kernel.
       -F flow label
              Allocate and set 20 bit flow label on echo request packets.  (Only ping6). If value is zero, kernel allocates random flow label.
       -f     Flood ping. For every ECHO_REQUEST sent a period ‘‘.’’ is printed, while for ever ECHO_REPLY received a backspace is printed.  This provides
              a rapid display of how many packets are being dropped.  If interval is not given, it sets interval to zero and outputs packets  as  fast  as
              they come back or one hundred times per second, whichever is more.  Only the super-user may use this option with zero interval.
       -i interval
              Wait  interval  seconds  between sending each packet.  The default is to wait for one second between each packet normally, or not to wait in
              flood mode. Only super-user may set interval to values less 0.2 seconds.
       -I interface address
              Set source address to specified interface address. Argument may be numeric IP address or  name  of  device.  When  pinging  IPv6  link-local
              address this option is required.
       -l preload
              If preload is specified, ping sends that many packets not waiting for reply.  Only the super-user may select preload more than 3.
       -L     Suppress loopback of multicast packets.  This flag only applies if the ping destination is a multicast address.
       -n     Numeric output only.  No attempt will be made to lookup symbolic names for host addresses.
       -p pattern
              You may specify up to 16 ‘‘pad’’ bytes to fill out the packet you send.  This is useful for diagnosing data-dependent problems in a network.
              For example, -p ff will cause the sent packet to be filled with all ones.
       -Q tos Set Quality of Service -related bits in ICMP datagrams.  tos can be either decimal or hex number.  Traditionally (RFC1349), these have  been
              interpreted  as: 0 for reserved (currently being redefined as congestion control), 1-4 for Type of Service and 5-7 for Precedence.  Possible
              settings for Type of Service are: minimal cost: 0x02, reliability: 0x04, throughput: 0x08, low delay: 0x10.  Multiple TOS bits should not be
              set  simultaneously.   Possible  settings  for  special  Precedence  range  from  priority  (0x20)  to net control (0xe0).  You must be root
              (CAP_NET_ADMIN capability) to use Critical or higher precedence value.  You cannot set bit 0x01 (reserved) unless ECN has  been  enabled  in
              the  kernel.   In  RFC2474,  these fields has been redefined as 8-bit Differentiated Services (DS), consisting of: bits 0-1 of separate data
              (ECN will be used, here), and bits 2-7 of Differentiated Services Codepoint (DSCP).
       -q     Quiet output.  Nothing is displayed except the summary lines at startup time and when finished.
       -R     Record route.  Includes the RECORD_ROUTE option in the ECHO_REQUEST packet and displays the route buffer on returned packets.  Note that the
              IP header is only large enough for nine such routes.  Many hosts ignore or discard this option.
       -r     Bypass  the  normal routing tables and send directly to a host on an attached interface.  If the host is not on a directly-attached network,
              an error is returned.  This option can be used to ping a local host through an interface that has no route through it provided the option -I
              is also used.
       -s packetsize
              Specifies  the  number of data bytes to be sent.  The default is 56, which translates into 64 ICMP data bytes when combined with the 8 bytes
              of ICMP header data.
       -S sndbuf
              Set socket sndbuf. If not specified, it is selected to buffer not more than one packet.
       -t ttl Set the IP Time to Live.
       -T timestamp option
              Set special IP timestamp options.  timestamp option may be either tsonly (only timestamps), tsandaddr (timestamps and addresses)  or  tspre-
              spec host1 [host2 [host3 [host4]]] (timestamp prespecified hops).
       -M hint
              Select  Path  MTU  Discovery  strategy.   hint  may be either do (prohibit fragmentation, even local one), want (do PMTU discovery, fragment
              locally when packet size is large), or dont (do not set DF flag).
       -U     Print full user-to-user latency (the old behaviour). Normally ping prints network round trip time, which can be different f.e.  due  to  DNS
              failures.
       -v     Verbose output.
       -V     Show version and exit.
       -w deadline
              Specify  a timeout, in seconds, before ping exits regardless of how many packets have been sent or received. In this case ping does not stop
              after count packet are sent, it waits either for deadline expire or until count probes are answered or for some error notification from net-
              work.
       -W timeout
              Time to wait for a response, in seconds. The option affects only timeout in absense of any responses, otherwise ping waits for two RTTs.
       When  using ping for fault isolation, it should first be run on the local host, to verify that the local network interface is up and running. Then,
       hosts and gateways further and further away should be ‘‘pinged’’. Round-trip times and packet loss statistics are computed.  If  duplicate  packets
       are  received, they are not included in the packet loss calculation, although the round trip time of these packets is used in calculating the mini-
       mum/average/maximum round-trip time numbers.  When the specified number of packets have been sent (and received) or if the  program  is  terminated
       with a SIGINT, a brief summary is displayed. Shorter current statistics can be obtained without termination of process with signal SIGQUIT.
       If ping does not receive any reply packets at all it will exit with code 1. If a packet count and deadline are both specified, and fewer than count
       packets are received by the time the deadline has arrived, it will also exit with code 1.  On other error it exits with code 2. Otherwise it  exits
       with code 0. This makes it possible to use the exit code to see if a host is alive or not.
       This program is intended for use in network testing, measurement and management.  Because of the load it can impose on the network, it is unwise to
       use ping during normal operations or from automated scripts.
ICMP PACKET DETAILS
       An IP header without options is 20 bytes.  An ICMP ECHO_REQUEST packet contains an additional 8 bytes worth of ICMP header followed by an arbitrary
       amount  of  data.   When  a  packetsize  is given, this indicated the size of this extra piece of data (the default is 56). Thus the amount of data
       received inside of an IP packet of type ICMP ECHO_REPLY will always be 8 bytes more than the requested data space (the ICMP header).
       If the data space is at least of size of struct timeval ping uses the beginning bytes of this space to include a timestamp which  it  uses  in  the
       computation of round trip times.  If the data space is shorter, no round trip times are given.
DUPLICATE AND DAMAGED PACKETS
       ping  will  report duplicate and damaged packets.  Duplicate packets should never occur, and seem to be caused by inappropriate link-level retrans-
       missions.  Duplicates may occur in many situations and are rarely (if ever) a good sign, although the presence of low levels of duplicates may  not
       always be cause for alarm.
       Damaged  packets are obviously serious cause for alarm and often indicate broken hardware somewhere in the ping packet’s path (in the network or in
       the hosts).
TRYING DIFFERENT DATA PATTERNS
       The (inter)network layer should never treat packets differently depending on the data contained in the data portion.  Unfortunately, data-dependent
       problems  have  been  known  to sneak into networks and remain undetected for long periods of time.  In many cases the particular pattern that will
       have problems is something that doesn’t have sufficient ‘‘transitions’’, such as all ones or all zeros, or a pattern right at  the  edge,  such  as
       almost all zeros.  It isn’t necessarily enough to specify a data pattern of all zeros (for example) on the command line because the pattern that is
       of interest is at the data link level, and the relationship between what you type and what the controllers transmit can be complicated.
       This means that if you have a data-dependent problem you will probably have to do a lot of testing to find it.  If you are lucky, you may manage to
       find  a  file  that  either  can’t be sent across your network or that takes much longer to transfer than other similar length files.  You can then
       examine this file for repeated patterns that you can test using the -p option of ping.
TTL DETAILS
       The TTL value of an IP packet represents the maximum number of IP routers that the packet can go through before  being  thrown  away.   In  current
       practice you can expect each router in the Internet to decrement the TTL field by exactly one.
       The  TCP/IP  specification states that the TTL field for TCP packets should be set to 60, but many systems use smaller values (4.3 BSD uses 30, 4.2
       used 15).
       The maximum possible value of this field is 255, and most Unix systems set the TTL field of ICMP ECHO_REQUEST packets to 255.  This is why you will
       find you can ‘‘ping’’ some hosts, but not reach them with telnet(1) or ftp(1).
       In  normal  operation  ping  prints the ttl value from the packet it receives.  When a remote system receives a ping packet, it can do one of three
       things with the TTL field in its response:
       Not change it; this is what Berkeley Unix systems did before the 4.3BSD Tahoe release. In this case the TTL value in the received packet will  be
         255 minus the number of routers in the round-trip path.
       Set  it to 255; this is what current Berkeley Unix systems do.  In this case the TTL value in the received packet will be 255 minus the number of
         routers in the path from the remote system to the pinging host.
       Set it to some other value. Some machines use the same value for ICMP packets that they use for TCP packets, for example either 30 or 60.  Others
         may use completely wild values.
BUGS
       Many Hosts and Gateways ignore the RECORD_ROUTE option.
       The  maximum  IP  header length is too small for options like RECORD_ROUTE to be completely useful.  There’s not much that that can be done about
         this, however.
       Flood pinging is not recommended in general, and flood pinging the broadcast address should only be done under very controlled conditions.
SEE ALSO
       netstat(1), ifconfig(8).
HISTORY
       The ping command appeared in 4.3BSD.
       The version described here is its descendant specific to Linux.
SECURITY
       ping requires CAP_NET_RAWIO capability to be executed. It may be used as set-uid root.
AVAILABILITY
       ping is part of iputils package and the latest versions are  available in source form at http://www.skbuff.net/iputils/iputils-current.tar.bz2.
iputils-071127                   19 July 2011                          PING(8)