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MAN page from Trustix iputils-0.0.20020927-8tr.i586.rpm

PING

Section: System Manager's Manual: iputils (8)
Updated: 27 September 2002
Index 

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_REQUESTdatagram to elicit an ICMP ECHO_RESPONSE from a host or gateway.ECHO_REQUEST datagrams (``pings'') have an IP and ICMPheader, followed by a struct timeval and then an arbitrarynumber of ``pad'' bytes used to fill out the packet. 

OPTIONS

-a
Audible ping.
-A
Adaptive ping. Interpacket interval adapts to round-trip time, so thateffectively not more than one (or more, if preload is set) unanswered probespresent 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_REQUESTpackets. With deadlineoption, ping waits forcount 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 andoutputs 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 intervalto values less 0.2 seconds.
-I interface address
Set source address to specified interface address. Argumentmay be numeric IP address or name of device. When pinging IPv6link-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 pingdestination 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 packetto 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 Serviceand 5-7 for Precedence.Possible settings for Type of Service are: minimal cost: 0x02, reliability: 0x04, throughput: 0x08, low delay: 0x10. Multiple TOS bitsshould not be set simultaneously. Possible settings forspecial Precedence range from priority (0x20) to net control (0xe0). Youmust be root (CAP_NET_ADMIN capability) to use Critical orhigher precedence value. You cannot setbit 0x01 (reserved) unless ECN has been enabled in the kernel.In RFC2474, these fields has been redefined as 8-bit DifferentiatedServices (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 andwhen finished.
-R
Record route.Includes the RECORD_ROUTE option in the ECHO_REQUESTpacket 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 attachedinterface.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 interfacethat has no route through it provided the option -I is alsoused.
-s packetsize
Specifies the number of data bytes to be sent. The default is 56, which translates into 64 ICMPdata bytes when combined with the 8 bytes of ICMP header data.
-S sndbuf
Set socket sndbuf. If not specified, it is selected to buffernot 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 tsprespec 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 sizeis large), or dont (do not set DF flag).
-U
Print full user-to-user latency (the old behaviour). Normallypingprints network round trip time, which can be differentf.e. due to DNS failures.
-v
Verbose output.
-V
Show version and exit.
-w deadline
Specify a timeout, in seconds, beforepingexits regardless of how manypackets have been sent or received. In this casepingdoes not stop aftercountpacket are sent, it waits either fordeadlineexpire or untilcountprobes are answered or for some error notification from network.
-W timeout
Time to wait for a response, in seconds. The option affects only timeoutin absense of any responses, otherwise ping waits for two RTTs.

When using ping for fault isolation, it should first be runon the local host, to verify that the local network interface is upand 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 packetloss calculation, although the round trip time of these packets is usedin calculating the minimum/average/maximum round-trip time numbers.When the specified number of packets have been sent (and received) orif the program is terminated with aSIGINT, a brief summary is displayed. Shorter current statisticscan be obtained without termination of process with signalSIGQUIT.

If ping does not receive any reply packets at all it willexit with code 1. If a packet countanddeadlineare both specified, and fewer thancountpackets are received by the time thedeadlinehas arrived, it will also exit with code 1. On other error it exits with code 2. Otherwise it exits with code 0. Thismakes it possible to use the exit code to see if a host is alive ornot.

This program is intended for use in network testing, measurement andmanagement.Because of the load it can impose on the network, it is unwise to useping 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 worthof ICMP header followed by an arbitrary amount of data.When a packetsize is given, this indicated the size of thisextra piece of data (the default is 56). Thus the amount of data receivedinside of an IP packet of type ICMP ECHO_REPLY will always be 8 bytesmore than the requested data space (the ICMP header).

If the data space is at least of size of struct timevalping uses the beginning bytes of this space to includea 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 byinappropriate link-level retransmissions.Duplicates may occur in many situations and are rarely (if ever) agood sign, although the presence of low levels of duplicates may notalways be cause for alarm.

Damaged packets are obviously serious cause for alarm and oftenindicate broken hardware somewhere in theping packet's path (in the network or in the hosts). 

TRYING DIFFERENT DATA PATTERNS

The (inter)network layer should never treat packets differently dependingon the data contained in the data portion.Unfortunately, data-dependent problems have been known to sneak intonetworks and remain undetected for long periods of time.In many cases the particular pattern that will have problems is somethingthat doesn't have sufficient ``transitions'', such as all ones or allzeros, 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 (forexample) on the command line because the pattern that is of interest isat the data link level, and the relationship between what you type andwhat the controllers transmit can be complicated.

This means that if you have a data-dependent problem you will probablyhave 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 sentacross your network or that takes much longer to transfer than othersimilar length files.You can then examine this file for repeated patterns that you can testusing the -p option of ping. 

TTL DETAILS

The TTL value of an IP packet represents the maximum number of IP routersthat the packet can go through before being thrown away.In current practice you can expect each router in the Internet to decrementthe TTL field by exactly one.

The TCP/IP specification states that the TTL field for TCPpackets 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 setthe TTL field of ICMP ECHO_REQUEST packets to 255.This is why you will find you can ``ping'' some hosts, but not reach themwithtelnet(1)orftp(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 thingswith the TTL field in its response:

*
Not change it; this is what Berkeley Unix systems did before the4.3BSD Tahoe release. In this case the TTL value in the received packetwill 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 thenumber of routers in the path fromthe remote system to the pinging host.
*
Set it to some other value. Some machines use the same value forICMP 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 likeRECORD_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 thebroadcast 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 capabilityto be executed. It may be used as set-uid root. 

AVAILABILITY

ping is part of iputils packageand the latest versions are available in source form for anonymous ftpftp://ftp.inr.ac.ru/ip-routing/iputils-current.tar.gz.


 

Index

NAME
SYNOPSIS
DESCRIPTION
OPTIONS
ICMP PACKET DETAILS
DUPLICATE AND DAMAGED PACKETS
TRYING DIFFERENT DATA PATTERNS
TTL DETAILS
BUGS
SEE ALSO
HISTORY
SECURITY
AVAILABILITY

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