【MTU】网络链路MTU大小测试

一、ping man 文档

# man ping > ping_manual.txt

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cat ping_manual.txt

PING(8)                                                                              System Manager's Manual: iputils                                                                             PING(8)



NAME
       ping - send ICMP ECHO_REQUEST to network hosts

SYNOPSIS
       ping  [-aAbBdDfhLnOqrRUvV46]  [-c  count] [-F flowlabel] [-i interval] [-I interface] [-l preload] [-m mark] [-M pmtudisc_option] [-N nodeinfo_option] [-w deadline] [-W timeout] [-p pattern] [-Q
       tos] [-s packetsize] [-S sndbuf] [-t ttl] [-T timestamp option] [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.

       ping works with both IPv4 and IPv6. Using only one of them explicitly can be enforced by specifying -4 or -6.

       ping can also send IPv6 Node Information Queries (RFC4620).  Intermediate hops may not be allowed, because IPv6 source routing was deprecated (RFC5095).

OPTIONS
       -4     Use IPv4 only.

       -6     Use IPv6 only.

       -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 probe is 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.

       -D     Print timestamp (unix time + microseconds as in gettimeofday) before each line.

       -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.

       -F flow label
              IPv6 only.  Allocate and set 20 bit flow label (in hex) on echo request packets.  If value is zero, kernel allocates random flow label.

       -h     Show help.

       -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
              interface  is  either  an  address,  or  an interface name.  If interface is an address, it sets source address to specified interface address.  If interface in an interface name, it sets
              source interface to specified interface.  For IPv6, when doing ping to a link-local scope address, link specification (by the '%'-notation in destination, or by 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.

       -m mark
              use mark to tag the packets going out. This is useful for variety of reasons within the kernel such as using policy routing to select specific outbound processing.

       -M pmtudisc_opt
              Select Path MTU Discovery strategy.  pmtudisc_option 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).

       -N nodeinfo_option
              IPv6 only.  Send ICMPv6 Node Information Queries (RFC4620), instead of Echo Request.  CAP_NET_RAW capability is required.

              help   Show help for NI support.

              name   Queries for Node Names.

              ipv6   Queries for IPv6 Addresses. There are several IPv6 specific flags.

                     ipv6-global
                            Request IPv6 global-scope addresses.

                     ipv6-sitelocal
                            Request IPv6 site-local addresses.

                     ipv6-linklocal
                            Request IPv6 link-local addresses.

                     ipv6-all
                            Request IPv6 addresses on other interfaces.

              ipv4   Queries for IPv4 Addresses.  There is one IPv4 specific flag.

                     ipv4-all
                            Request IPv4 addresses on other interfaces.

              subject-ipv6=ipv6addr
                     IPv6 subject address.

              subject-ipv4=ipv4addr
                     IPv4 subject address.

              subject-name=nodename
                     Subject name.  If it contains more than one dot, fully-qualified domain name is assumed.

              subject-fqdn=nodename
                     Subject name.  Fully-qualified domain name is always assumed.

       -n     Numeric output only.  No attempt will be made to lookup symbolic names for host addresses.

       -O     Report outstanding ICMP ECHO reply before sending next packet.  This is useful together with the timestamp -D to log output to a diagnostic file and search for missing answers.

       -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     Quiet output.  Nothing is displayed except the summary lines at startup time and when finished.

       -Q tos Set Quality of Service -related bits in ICMP datagrams.  tos can be decimal (ping only) or hex number.

              In RFC2474, these fields are interpreted as 8-bit Differentiated Services (DS), consisting of: bits 0-1 (2 lowest bits) of separate data, and bits 2-7 (highest 6 bits)  of  Differentiated
              Services Codepoint (DSCP).  In RFC2481 and RFC3168, bits 0-1 are used for ECN.

              Historically  (RFC1349,  obsoleted  by  RFC2474), these were interpreted as: bit 0 (lowest bit) for reserved (currently being redefined as congestion control), 1-4 for Type of Service and
              bits 5-7 (highest bits) for Precedence.

       -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.

       -R     ping only.  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.

       -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 ping only.  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 tsprespec host1 [host2 [host3 [host4]]] (timestamp pre‐
              specified hops).

       -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 network.

       -W timeout
              Time to wait for a response, in seconds. The option affects only timeout in absence 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 minimum/average/maximum round-trip time numbers.  When the specified number of packets have been sent (and received) or if the program is  termi‐
       nated 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 retransmissions.  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 net‐
       works 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 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.

       As of version s20150815, the ping6 binary doesn't exist anymore.  It has been merged into ping. Creating a symlink named ping6 pointing to ping will result in the same funcionality as before.

SECURITY
       ping  requires  CAP_NET_RAW  capability to be executed 1) if the program is used for non-echo queries (See -N option), or 2) if kernel does not support non-raw ICMP sockets, or 3) if the user is
       not allowed to create an ICMP echo socket.  The program 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-160308                                             
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二、协议头大小

icmp header: 8 bytes

ip header: 20 bytes

tcp header: 20 bytes

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三、各系统 MTU 大小测试

Linux

# ping  -s 1472 -M  do  www.example.com
PING www.example.com (93.184.216.34) 1472(1500) bytes of data.
1480 bytes from 93.184.216.34 (93.184.216.34): icmp_seq=1 ttl=47 time=168 ms
1480 bytes from 93.184.216.34 (93.184.216.34): icmp_seq=2 ttl=47 time=168 ms

--- www.example.com ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 1000ms
rtt min/avg/max/mdev = 168.119/168.123/168.127/0.004 ms

# ping  -s 1473 -M  do  www.example.com
PING www.example.com (93.184.216.34) 1473(1501) bytes of data.
ping: local error: Message too long, mtu=1500
ping: local error: Message too long, mtu=1500

--- www.example.com ping statistics ---
2 packets transmitted, 0 received, +2 errors, 100% packet loss, time 999ms

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###Windows

ping  -l  1472  -f   www.example.com
ping  -l  1473  -f   www.example.com

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ping  -l  1440  -f   www.example.com
ping  -l  1441  -f   www.example.com

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四、参考

ping/dig/nslookup 三件套
https://www.jianshu.com/p/2940c10a33c1

MTU和MSS
https://www.jianshu.com/p/399049fa1648

用wireshark分析 ICMP协议报文
https://www.jianshu.com/p/61b31c446419

MTU、IP MTU 和 MSS
https://www.jianshu.com/p/6232ba4687f2