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diff --git a/contrib/tcpdump/tcpdump.1 b/contrib/tcpdump/tcpdump.1 new file mode 100644 index 0000000..1dc0340f --- /dev/null +++ b/contrib/tcpdump/tcpdump.1 @@ -0,0 +1,2362 @@ +.\" @(#) $Header: /tcpdump/master/tcpdump/tcpdump.1,v 1.167.2.6 2005/09/05 09:14:37 guy Exp $ (LBL) +.\" +.\" $NetBSD: tcpdump.8,v 1.9 2003/03/31 00:18:17 perry Exp $ +.\" +.\" Copyright (c) 1987, 1988, 1989, 1990, 1991, 1992, 1994, 1995, 1996, 1997 +.\" The Regents of the University of California. All rights reserved. +.\" All rights reserved. +.\" +.\" Redistribution and use in source and binary forms, with or without +.\" modification, are permitted provided that: (1) source code distributions +.\" retain the above copyright notice and this paragraph in its entirety, (2) +.\" distributions including binary code include the above copyright notice and +.\" this paragraph in its entirety in the documentation or other materials +.\" provided with the distribution, and (3) all advertising materials mentioning +.\" features or use of this software display the following acknowledgement: +.\" ``This product includes software developed by the University of California, +.\" Lawrence Berkeley Laboratory and its contributors.'' Neither the name of +.\" the University nor the names of its contributors may be used to endorse +.\" or promote products derived from this software without specific prior +.\" written permission. +.\" THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED +.\" WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF +.\" MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. +.\" +.\" $FreeBSD$ +.\" +.TH TCPDUMP 1 "18 April 2005" +.SH NAME +tcpdump \- dump traffic on a network +.SH SYNOPSIS +.na +.B tcpdump +[ +.B \-AdDeflLnNOpqRStuUvxX +] [ +.B \-c +.I count +] +.br +.ti +8 +[ +.B \-C +.I file_size +] [ +.B \-F +.I file +] +.br +.ti +8 +[ +.B \-i +.I interface +] +[ +.B \-m +.I module +] +[ +.B \-M +.I secret +] +.br +.ti +8 +[ +.B \-r +.I file +] +[ +.B \-s +.I snaplen +] +[ +.B \-T +.I type +] +[ +.B \-w +.I file +] +.br +.ti +8 +[ +.B \-W +.I filecount +] +.br +.ti +8 +[ +.B \-E +.I spi@ipaddr algo:secret,... +] +.br +.ti +8 +[ +.B \-y +.I datalinktype +] +[ +.B \-Z +.I user +] +.ti +8 +[ +.B \-y +.I datalinktype +] +.ti +8 +[ +.I expression +] +.br +.ad +.SH DESCRIPTION +.LP +\fITcpdump\fP prints out the headers of packets on a network interface +that match the boolean \fIexpression\fP. It can also be run with the +.B \-w +flag, which causes it to save the packet data to a file for later +analysis, and/or with the +.B \-r +flag, which causes it to read from a saved packet file rather than to +read packets from a network interface. In all cases, only packets that +match +.I expression +will be processed by +.IR tcpdump . +.LP +.I Tcpdump +will, if not run with the +.B \-c +flag, continue capturing packets until it is interrupted by a SIGINT +signal (generated, for example, by typing your interrupt character, +typically control-C) or a SIGTERM signal (typically generated with the +.BR kill (1) +command); if run with the +.B \-c +flag, it will capture packets until it is interrupted by a SIGINT or +SIGTERM signal or the specified number of packets have been processed. +.LP +When +.I tcpdump +finishes capturing packets, it will report counts of: +.IP +packets ``captured'' (this is the number of packets that +.I tcpdump +has received and processed); +.IP +packets ``received by filter'' (the meaning of this depends on the OS on +which you're running +.IR tcpdump , +and possibly on the way the OS was configured - if a filter was +specified on the command line, on some OSes it counts packets regardless +of whether they were matched by the filter expression and, even if they +were matched by the filter expression, regardless of whether +.I tcpdump +has read and processed them yet, on other OSes it counts only packets that were +matched by the filter expression regardless of whether +.I tcpdump +has read and processed them yet, and on other OSes it counts only +packets that were matched by the filter expression and were processed by +.IR tcpdump ); +.IP +packets ``dropped by kernel'' (this is the number of packets that were +dropped, due to a lack of buffer space, by the packet capture mechanism +in the OS on which +.I tcpdump +is running, if the OS reports that information to applications; if not, +it will be reported as 0). +.LP +On platforms that support the SIGINFO signal, such as most BSDs +(including Mac OS X) and Digital/Tru64 UNIX, it will report those counts +when it receives a SIGINFO signal (generated, for example, by typing +your ``status'' character, typically control-T, although on some +platforms, such as Mac OS X, the ``status'' character is not set by +default, so you must set it with +.BR stty (1) +in order to use it) and will continue capturing packets. +.LP +Reading packets from a network interface may require that you have +special privileges: +.TP +.B Under SunOS 3.x or 4.x with NIT or BPF: +You must have read access to +.I /dev/nit +or +.IR /dev/bpf* . +.TP +.B Under Solaris with DLPI: +You must have read/write access to the network pseudo device, e.g. +.IR /dev/le . +On at least some versions of Solaris, however, this is not sufficient to +allow +.I tcpdump +to capture in promiscuous mode; on those versions of Solaris, you must +be root, or +.I tcpdump +must be installed setuid to root, in order to capture in promiscuous +mode. Note that, on many (perhaps all) interfaces, if you don't capture +in promiscuous mode, you will not see any outgoing packets, so a capture +not done in promiscuous mode may not be very useful. +.TP +.B Under HP-UX with DLPI: +You must be root or +.I tcpdump +must be installed setuid to root. +.TP +.B Under IRIX with snoop: +You must be root or +.I tcpdump +must be installed setuid to root. +.TP +.B Under Linux: +You must be root or +.I tcpdump +must be installed setuid to root (unless your distribution has a kernel +that supports capability bits such as CAP_NET_RAW and code to allow +those capability bits to be given to particular accounts and to cause +those bits to be set on a user's initial processes when they log in, in +which case you must have CAP_NET_RAW in order to capture and +CAP_NET_ADMIN to enumerate network devices with, for example, the +.B \-D +flag). +.TP +.B Under ULTRIX and Digital UNIX/Tru64 UNIX: +Any user may capture network traffic with +.IR tcpdump . +However, no user (not even the super-user) can capture in promiscuous +mode on an interface unless the super-user has enabled promiscuous-mode +operation on that interface using +.IR pfconfig (8), +and no user (not even the super-user) can capture unicast traffic +received by or sent by the machine on an interface unless the super-user +has enabled copy-all-mode operation on that interface using +.IR pfconfig , +so +.I useful +packet capture on an interface probably requires that either +promiscuous-mode or copy-all-mode operation, or both modes of +operation, be enabled on that interface. +.TP +.B Under BSD (this includes Mac OS X): +You must have read access to +.IR /dev/bpf* . +On BSDs with a devfs (this includes Mac OS X), this might involve more +than just having somebody with super-user access setting the ownership +or permissions on the BPF devices - it might involve configuring devfs +to set the ownership or permissions every time the system is booted, +if the system even supports that; if it doesn't support that, you might +have to find some other way to make that happen at boot time. +.LP +Reading a saved packet file doesn't require special privileges. +.SH OPTIONS +.TP +.B \-A +Print each packet (minus its link level header) in ASCII. Handy for +capturing web pages. +.TP +.B \-c +Exit after receiving \fIcount\fP packets. +.TP +.B \-C +Before writing a raw packet to a savefile, check whether the file is +currently larger than \fIfile_size\fP and, if so, close the current +savefile and open a new one. Savefiles after the first savefile will +have the name specified with the +.B \-w +flag, with a number after it, starting at 1 and continuing upward. +The units of \fIfile_size\fP are millions of bytes (1,000,000 bytes, +not 1,048,576 bytes). +.TP +.B \-d +Dump the compiled packet-matching code in a human readable form to +standard output and stop. +.TP +.B \-dd +Dump packet-matching code as a +.B C +program fragment. +.TP +.B \-ddd +Dump packet-matching code as decimal numbers (preceded with a count). +.TP +.B \-D +Print the list of the network interfaces available on the system and on +which +.I tcpdump +can capture packets. For each network interface, a number and an +interface name, possibly followed by a text description of the +interface, is printed. The interface name or the number can be supplied +to the +.B \-i +flag to specify an interface on which to capture. +.IP +This can be useful on systems that don't have a command to list them +(e.g., Windows systems, or UNIX systems lacking +.BR "ifconfig \-a" ); +the number can be useful on Windows 2000 and later systems, where the +interface name is a somewhat complex string. +.IP +The +.B \-D +flag will not be supported if +.I tcpdump +was built with an older version of +.I libpcap +that lacks the +.B pcap_findalldevs() +function. +.TP +.B \-e +Print the link-level header on each dump line. +.TP +.B \-E +Use \fIspi@ipaddr algo:secret\fP for decrypting IPsec ESP packets that +are addressed to \fIaddr\fP and contain Security Parameter Index value +\fIspi\fP. This combination may be repeated with comma or newline seperation. +.IP +Note that setting the secret for IPv4 ESP packets is supported at this time. +.IP +Algorithms may be +\fBdes-cbc\fP, +\fB3des-cbc\fP, +\fBblowfish-cbc\fP, +\fBrc3-cbc\fP, +\fBcast128-cbc\fP, or +\fBnone\fP. +The default is \fBdes-cbc\fP. +The ability to decrypt packets is only present if \fItcpdump\fP was compiled +with cryptography enabled. +.IP +\fIsecret\fP is the ASCII text for ESP secret key. +If preceeded by 0x, then a hex value will be read. +.IP +The option assumes RFC2406 ESP, not RFC1827 ESP. +The option is only for debugging purposes, and +the use of this option with a true `secret' key is discouraged. +By presenting IPsec secret key onto command line +you make it visible to others, via +.IR ps (1) +and other occasions. +.IP +In addition to the above syntax, the syntax \fIfile name\fP may be used +to have tcpdump read the provided file in. The file is opened upon +receiving the first ESP packet, so any special permissions that tcpdump +may have been given should already have been given up. +.TP +.B \-f +Print `foreign' IPv4 addresses numerically rather than symbolically +(this option is intended to get around serious brain damage in +Sun's NIS server \(em usually it hangs forever translating non-local +internet numbers). +.IP +The test for `foreign' IPv4 addresses is done using the IPv4 address and +netmask of the interface on which capture is being done. If that +address or netmask are not available, available, either because the +interface on which capture is being done has no address or netmask or +because the capture is being done on the Linux "any" interface, which +can capture on more than one interface, this option will not work +correctly. +.TP +.B \-F +Use \fIfile\fP as input for the filter expression. +An additional expression given on the command line is ignored. +.TP +.B \-i +Listen on \fIinterface\fP. +If unspecified, \fItcpdump\fP searches the system interface list for the +lowest numbered, configured up interface (excluding loopback). +Ties are broken by choosing the earliest match. +.IP +On Linux systems with 2.2 or later kernels, an +.I interface +argument of ``any'' can be used to capture packets from all interfaces. +Note that captures on the ``any'' device will not be done in promiscuous +mode. +.IP +If the +.B \-D +flag is supported, an interface number as printed by that flag can be +used as the +.I interface +argument. +.TP +.B \-l +Make stdout line buffered. +Useful if you want to see the data +while capturing it. +E.g., +.br +``tcpdump\ \ \-l\ \ |\ \ tee dat'' or +``tcpdump\ \ \-l \ \ > dat\ \ &\ \ tail\ \ \-f\ \ dat''. +.TP +.B \-L +List the known data link types for the interface and exit. +.TP +.B \-m +Load SMI MIB module definitions from file \fImodule\fR. +This option +can be used several times to load several MIB modules into \fItcpdump\fP. +.TP +.B \-M +Use \fIsecret\fP as a shared secret for validating the digests found in +TCP segments with the TCP-MD5 option (RFC 2385), if present. +.TP +.B \-n +Don't convert addresses (i.e., host addresses, port numbers, etc.) to names. +.TP +.B \-N +Don't print domain name qualification of host names. +E.g., +if you give this flag then \fItcpdump\fP will print ``nic'' +instead of ``nic.ddn.mil''. +.TP +.B \-O +Do not run the packet-matching code optimizer. +This is useful only +if you suspect a bug in the optimizer. +.TP +.B \-p +\fIDon't\fP put the interface +into promiscuous mode. +Note that the interface might be in promiscuous +mode for some other reason; hence, `-p' cannot be used as an abbreviation for +`ether host {local-hw-addr} or ether broadcast'. +.TP +.B \-q +Quick (quiet?) output. +Print less protocol information so output +lines are shorter. +.TP +.B \-R +Assume ESP/AH packets to be based on old specification (RFC1825 to RFC1829). +If specified, \fItcpdump\fP will not print replay prevention field. +Since there is no protocol version field in ESP/AH specification, +\fItcpdump\fP cannot deduce the version of ESP/AH protocol. +.TP +.B \-r +Read packets from \fIfile\fR (which was created with the +.B \-w +option). +Standard input is used if \fIfile\fR is ``-''. +.TP +.B \-S +Print absolute, rather than relative, TCP sequence numbers. +.TP +.B \-s +Snarf \fIsnaplen\fP bytes of data from each packet rather than the +default of 68 (with SunOS's NIT, the minimum is actually 96). +68 bytes is adequate for IP, ICMP, TCP +and UDP but may truncate protocol information from name server and NFS +packets (see below). +Packets truncated because of a limited snapshot +are indicated in the output with ``[|\fIproto\fP]'', where \fIproto\fP +is the name of the protocol level at which the truncation has occurred. +Note that taking larger snapshots both increases +the amount of time it takes to process packets and, effectively, +decreases the amount of packet buffering. +This may cause packets to be +lost. +You should limit \fIsnaplen\fP to the smallest number that will +capture the protocol information you're interested in. +Setting +\fIsnaplen\fP to 0 means use the required length to catch whole packets. +.TP +.B \-T +Force packets selected by "\fIexpression\fP" to be interpreted the +specified \fItype\fR. +Currently known types are +\fBaodv\fR (Ad-hoc On-demand Distance Vector protocol), +\fBcnfp\fR (Cisco NetFlow protocol), +\fBrpc\fR (Remote Procedure Call), +\fBrtp\fR (Real-Time Applications protocol), +\fBrtcp\fR (Real-Time Applications control protocol), +\fBsnmp\fR (Simple Network Management Protocol), +\fBtftp\fR (Trivial File Transfer Protocol), +\fBvat\fR (Visual Audio Tool), +and +\fBwb\fR (distributed White Board). +.TP +.B \-t +\fIDon't\fP print a timestamp on each dump line. +.TP +.B \-tt +Print an unformatted timestamp on each dump line. +.TP +.B \-ttt +Print a delta (in micro-seconds) between current and previous line +on each dump line. +.TP +.B \-tttt +Print a timestamp in default format proceeded by date on each dump line. +.TP +.B \-u +Print undecoded NFS handles. +.TP +.B \-U +Make output saved via the +.B \-w +option ``packet-buffered''; i.e., as each packet is saved, it will be +written to the output file, rather than being written only when the +output buffer fills. +.IP +The +.B \-U +flag will not be supported if +.I tcpdump +was built with an older version of +.I libpcap +that lacks the +.B pcap_dump_flush() +function. +.TP +.B \-v +When parsing and printing, produce (slightly more) verbose output. +For example, the time to live, +identification, total length and options in an IP packet are printed. +Also enables additional packet integrity checks such as verifying the +IP and ICMP header checksum. +.IP +When writing to a file with the +.B \-w +option, report, every 10 seconds, the number of packets captured. +.TP +.B \-vv +Even more verbose output. +For example, additional fields are +printed from NFS reply packets, and SMB packets are fully decoded. +.TP +.B \-vvv +Even more verbose output. +For example, +telnet \fBSB\fP ... \fBSE\fP options +are printed in full. +With +.B \-X +Telnet options are printed in hex as well. +.TP +.B \-w +Write the raw packets to \fIfile\fR rather than parsing and printing +them out. +They can later be printed with the \-r option. +Standard output is used if \fIfile\fR is ``-''. +.TP +.B \-W +Used in conjunction with the +.I \-C +option, this will limit the number +of files created to the specified number, and begin overwriting files +from the beginning, thus creating a 'rotating' buffer. +In addition, it will name +the files with enough leading 0s to support the maximum number of +files, allowing them to sort correctly. +.TP +.B \-x +Print each packet (minus its link level header) in hex. +The smaller of the entire packet or +.I snaplen +bytes will be printed. Note that this is the entire link-layer +packet, so for link layers that pad (e.g. Ethernet), the padding bytes +will also be printed when the higher layer packet is shorter than the +required padding. +.TP +.B \-xx +Print each packet, +.I including +its link level header, in hex. +.TP +.B \-X +Print each packet (minus its link level header) in hex and ASCII. +This is very handy for analysing new protocols. +.TP +.B \-XX +Print each packet, +.I including +its link level header, in hex and ASCII. +.TP +.B \-y +Set the data link type to use while capturing packets to \fIdatalinktype\fP. +.TP +.B \-Z +Drops privileges (if root) and changes user ID to +.I user +and the group ID to the primary group of +.IR user . +.IP +This behavior can also be enabled by default at compile time. +.IP "\fI expression\fP" +.RS +selects which packets will be dumped. +If no \fIexpression\fP +is given, all packets on the net will be dumped. +Otherwise, +only packets for which \fIexpression\fP is `true' will be dumped. +.LP +The \fIexpression\fP consists of one or more +.I primitives. +Primitives usually consist of an +.I id +(name or number) preceded by one or more qualifiers. +There are three +different kinds of qualifier: +.IP \fItype\fP +qualifiers say what kind of thing the id name or number refers to. +Possible types are +.BR host , +.B net , +.B port +and +.BR portrange . +E.g., `host foo', `net 128.3', `port 20', `portrange 6000-6008'. +If there is no type +qualifier, +.B host +is assumed. +.IP \fIdir\fP +qualifiers specify a particular transfer direction to and/or from +.IR id . +Possible directions are +.BR src , +.BR dst , +.B "src or dst" +and +.B "src and" +.BR dst . +E.g., `src foo', `dst net 128.3', `src or dst port ftp-data'. +If +there is no dir qualifier, +.B "src or dst" +is assumed. +For some link layers, such as SLIP and the ``cooked'' Linux capture mode +used for the ``any'' device and for some other device types, the +.B inbound +and +.B outbound +qualifiers can be used to specify a desired direction. +.IP \fIproto\fP +qualifiers restrict the match to a particular protocol. +Possible +protos are: +.BR ether , +.BR fddi , +.BR tr , +.BR wlan , +.BR ip , +.BR ip6 , +.BR arp , +.BR rarp , +.BR decnet , +.BR lat , +.BR sca , +.BR moprc , +.BR mopdl , +.BR iso , +.BR esis , +.BR isis , +.BR icmp , +.BR icmp6 , +.B tcp +and +.BR udp . +E.g., `ether src foo', `arp net 128.3', `tcp port 21', `udp portrange +7000-7009'. +If there is +no proto qualifier, all protocols consistent with the type are +assumed. +E.g., `src foo' means `(ip or arp or rarp) src foo' +(except the latter is not legal syntax), `net bar' means `(ip or +arp or rarp) net bar' and `port 53' means `(tcp or udp) port 53'. +.LP +[`fddi' is actually an alias for `ether'; the parser treats them +identically as meaning ``the data link level used on the specified +network interface.'' FDDI headers contain Ethernet-like source +and destination addresses, and often contain Ethernet-like packet +types, so you can filter on these FDDI fields just as with the +analogous Ethernet fields. +FDDI headers also contain other fields, +but you cannot name them explicitly in a filter expression. +.LP +Similarly, `tr' and `wlan' are aliases for `ether'; the previous +paragraph's statements about FDDI headers also apply to Token Ring +and 802.11 wireless LAN headers. For 802.11 headers, the destination +address is the DA field and the source address is the SA field; the +BSSID, RA, and TA fields aren't tested.] +.LP +In addition to the above, there are some special `primitive' keywords +that don't follow the pattern: +.BR gateway , +.BR broadcast , +.BR less , +.B greater +and arithmetic expressions. +All of these are described below. +.LP +More complex filter expressions are built up by using the words +.BR and , +.B or +and +.B not +to combine primitives. +E.g., `host foo and not port ftp and not port ftp-data'. +To save typing, identical qualifier lists can be omitted. +E.g., +`tcp dst port ftp or ftp-data or domain' is exactly the same as +`tcp dst port ftp or tcp dst port ftp-data or tcp dst port domain'. +.LP +Allowable primitives are: +.IP "\fBdst host \fIhost\fR" +True if the IPv4/v6 destination field of the packet is \fIhost\fP, +which may be either an address or a name. +.IP "\fBsrc host \fIhost\fR" +True if the IPv4/v6 source field of the packet is \fIhost\fP. +.IP "\fBhost \fIhost\fP +True if either the IPv4/v6 source or destination of the packet is \fIhost\fP. +.IP +Any of the above host expressions can be prepended with the keywords, +\fBip\fP, \fBarp\fP, \fBrarp\fP, or \fBip6\fP as in: +.in +.5i +.nf +\fBip host \fIhost\fR +.fi +.in -.5i +which is equivalent to: +.in +.5i +.nf +\fBether proto \fI\\ip\fB and host \fIhost\fR +.fi +.in -.5i +If \fIhost\fR is a name with multiple IP addresses, each address will +be checked for a match. +.IP "\fBether dst \fIehost\fP +True if the Ethernet destination address is \fIehost\fP. +\fIEhost\fP +may be either a name from /etc/ethers or a number (see +.IR ethers (3N) +for numeric format). +.IP "\fBether src \fIehost\fP +True if the Ethernet source address is \fIehost\fP. +.IP "\fBether host \fIehost\fP +True if either the Ethernet source or destination address is \fIehost\fP. +.IP "\fBgateway\fP \fIhost\fP +True if the packet used \fIhost\fP as a gateway. +I.e., the Ethernet +source or destination address was \fIhost\fP but neither the IP source +nor the IP destination was \fIhost\fP. +\fIHost\fP must be a name and +must be found both by the machine's host-name-to-IP-address resolution +mechanisms (host name file, DNS, NIS, etc.) and by the machine's +host-name-to-Ethernet-address resolution mechanism (/etc/ethers, etc.). +(An equivalent expression is +.in +.5i +.nf +\fBether host \fIehost \fBand not host \fIhost\fR +.fi +.in -.5i +which can be used with either names or numbers for \fIhost / ehost\fP.) +This syntax does not work in IPv6-enabled configuration at this moment. +.IP "\fBdst net \fInet\fR" +True if the IPv4/v6 destination address of the packet has a network +number of \fInet\fP. +\fINet\fP may be either a name from /etc/networks +or a network number (see \fInetworks(4)\fP for details). +.IP "\fBsrc net \fInet\fR" +True if the IPv4/v6 source address of the packet has a network +number of \fInet\fP. +.IP "\fBnet \fInet\fR" +True if either the IPv4/v6 source or destination address of the packet has a network +number of \fInet\fP. +.IP "\fBnet \fInet\fR \fBmask \fInetmask\fR" +True if the IPv4 address matches \fInet\fR with the specific \fInetmask\fR. +May be qualified with \fBsrc\fR or \fBdst\fR. +Note that this syntax is not valid for IPv6 \fInet\fR. +.IP "\fBnet \fInet\fR/\fIlen\fR" +True if the IPv4/v6 address matches \fInet\fR with a netmask \fIlen\fR +bits wide. +May be qualified with \fBsrc\fR or \fBdst\fR. +.IP "\fBdst port \fIport\fR" +True if the packet is ip/tcp, ip/udp, ip6/tcp or ip6/udp and has a +destination port value of \fIport\fP. +The \fIport\fP can be a number or a name used in /etc/services (see +.IR tcp (4P) +and +.IR udp (4P)). +If a name is used, both the port +number and protocol are checked. +If a number or ambiguous name is used, +only the port number is checked (e.g., \fBdst port 513\fR will print both +tcp/login traffic and udp/who traffic, and \fBport domain\fR will print +both tcp/domain and udp/domain traffic). +.IP "\fBsrc port \fIport\fR" +True if the packet has a source port value of \fIport\fP. +.IP "\fBport \fIport\fR" +True if either the source or destination port of the packet is \fIport\fP. +.IP "\fBdst portrange \fIport1\fB-\fIport2\fR" +True if the packet is ip/tcp, ip/udp, ip6/tcp or ip6/udp and has a +destination port value between \fIport1\fP and \fIport2\fP. +.I port1 +and +.I port2 +are interpreted in the same fashion as the +.I port +parameter for +.BR port . +.IP "\fBsrc portrange \fIport1\fB-\fIport2\fR" +True if the packet has a source port value between \fIport1\fP and +\fIport2\fP. +.IP "\fBportrange \fIport1\fB-\fIport2\fR" +True if either the source or destination port of the packet is between +\fIport1\fP and \fIport2\fP. +.IP +Any of the above port or port range expressions can be prepended with +the keywords, \fBtcp\fP or \fBudp\fP, as in: +.in +.5i +.nf +\fBtcp src port \fIport\fR +.fi +.in -.5i +which matches only tcp packets whose source port is \fIport\fP. +.IP "\fBless \fIlength\fR" +True if the packet has a length less than or equal to \fIlength\fP. +This is equivalent to: +.in +.5i +.nf +\fBlen <= \fIlength\fP. +.fi +.in -.5i +.IP "\fBgreater \fIlength\fR" +True if the packet has a length greater than or equal to \fIlength\fP. +This is equivalent to: +.in +.5i +.nf +\fBlen >= \fIlength\fP. +.fi +.in -.5i +.IP "\fBip proto \fIprotocol\fR" +True if the packet is an IPv4 packet (see +.IR ip (4P)) +of protocol type \fIprotocol\fP. +\fIProtocol\fP can be a number or one of the names +\fBicmp\fP, \fBicmp6\fP, \fBigmp\fP, \fBigrp\fP, \fBpim\fP, \fBah\fP, +\fBesp\fP, \fBvrrp\fP, \fBudp\fP, or \fBtcp\fP. +Note that the identifiers \fBtcp\fP, \fBudp\fP, and \fBicmp\fP are also +keywords and must be escaped via backslash (\\), which is \\\\ in the C-shell. +Note that this primitive does not chase the protocol header chain. +.IP "\fBip6 proto \fIprotocol\fR" +True if the packet is an IPv6 packet of protocol type \fIprotocol\fP. +Note that this primitive does not chase the protocol header chain. +.IP "\fBip6 protochain \fIprotocol\fR" +True if the packet is IPv6 packet, +and contains protocol header with type \fIprotocol\fR +in its protocol header chain. +For example, +.in +.5i +.nf +\fBip6 protochain 6\fR +.fi +.in -.5i +matches any IPv6 packet with TCP protocol header in the protocol header chain. +The packet may contain, for example, +authentication header, routing header, or hop-by-hop option header, +between IPv6 header and TCP header. +The BPF code emitted by this primitive is complex and +cannot be optimized by BPF optimizer code in \fItcpdump\fP, +so this can be somewhat slow. +.IP "\fBip protochain \fIprotocol\fR" +Equivalent to \fBip6 protochain \fIprotocol\fR, but this is for IPv4. +.IP "\fBether broadcast\fR" +True if the packet is an Ethernet broadcast packet. +The \fIether\fP +keyword is optional. +.IP "\fBip broadcast\fR" +True if the packet is an IPv4 broadcast packet. +It checks for both the all-zeroes and all-ones broadcast conventions, +and looks up the subnet mask on the interface on which the capture is +being done. +.IP +If the subnet mask of the interface on which the capture is being done +is not available, either because the interface on which capture is being +done has no netmask or because the capture is being done on the Linux +"any" interface, which can capture on more than one interface, this +check will not work correctly. +.IP "\fBether multicast\fR" +True if the packet is an Ethernet multicast packet. +The \fBether\fP +keyword is optional. +This is shorthand for `\fBether[0] & 1 != 0\fP'. +.IP "\fBip multicast\fR" +True if the packet is an IPv4 multicast packet. +.IP "\fBip6 multicast\fR" +True if the packet is an IPv6 multicast packet. +.IP "\fBether proto \fIprotocol\fR" +True if the packet is of ether type \fIprotocol\fR. +\fIProtocol\fP can be a number or one of the names +\fBip\fP, \fBip6\fP, \fBarp\fP, \fBrarp\fP, \fBatalk\fP, \fBaarp\fP, +\fBdecnet\fP, \fBsca\fP, \fBlat\fP, \fBmopdl\fP, \fBmoprc\fP, +\fBiso\fP, \fBstp\fP, \fBipx\fP, or \fBnetbeui\fP. +Note these identifiers are also keywords +and must be escaped via backslash (\\). +.IP +[In the case of FDDI (e.g., `\fBfddi protocol arp\fR'), Token Ring +(e.g., `\fBtr protocol arp\fR'), and IEEE 802.11 wireless LANS (e.g., +`\fBwlan protocol arp\fR'), for most of those protocols, the +protocol identification comes from the 802.2 Logical Link Control (LLC) +header, which is usually layered on top of the FDDI, Token Ring, or +802.11 header. +.IP +When filtering for most protocol identifiers on FDDI, Token Ring, or +802.11, \fItcpdump\fR checks only the protocol ID field of an LLC header +in so-called SNAP format with an Organizational Unit Identifier (OUI) of +0x000000, for encapsulated Ethernet; it doesn't check whether the packet +is in SNAP format with an OUI of 0x000000. +The exceptions are: +.RS +.TP +\fBiso\fP +\fItcpdump\fR checks the DSAP (Destination Service Access Point) and +SSAP (Source Service Access Point) fields of the LLC header; +.TP +\fBstp\fP and \fBnetbeui\fP +\fItcpdump\fR checks the DSAP of the LLC header; +.TP +\fBatalk\fP +\fItcpdump\fR checks for a SNAP-format packet with an OUI of 0x080007 +and the AppleTalk etype. +.RE +.IP +In the case of Ethernet, \fItcpdump\fR checks the Ethernet type field +for most of those protocols. The exceptions are: +.RS +.TP +\fBiso\fP, \fBstp\fP, and \fBnetbeui\fP +\fItcpdump\fR checks for an 802.3 frame and then checks the LLC header as +it does for FDDI, Token Ring, and 802.11; +.TP +\fBatalk\fP +\fItcpdump\fR checks both for the AppleTalk etype in an Ethernet frame and +for a SNAP-format packet as it does for FDDI, Token Ring, and 802.11; +.TP +\fBaarp\fP +\fItcpdump\fR checks for the AppleTalk ARP etype in either an Ethernet +frame or an 802.2 SNAP frame with an OUI of 0x000000; +.TP +\fBipx\fP +\fItcpdump\fR checks for the IPX etype in an Ethernet frame, the IPX +DSAP in the LLC header, the 802.3-with-no-LLC-header encapsulation of +IPX, and the IPX etype in a SNAP frame. +.RE +.IP "\fBdecnet src \fIhost\fR" +True if the DECNET source address is +.IR host , +which may be an address of the form ``10.123'', or a DECNET host +name. +[DECNET host name support is only available on ULTRIX systems +that are configured to run DECNET.] +.IP "\fBdecnet dst \fIhost\fR" +True if the DECNET destination address is +.IR host . +.IP "\fBdecnet host \fIhost\fR" +True if either the DECNET source or destination address is +.IR host . +.IP "\fBifname \fIinterface\fR" +True if the packet was logged as coming from the specified interface (applies +only to packets logged by OpenBSD's +.BR pf (4)). +.IP "\fBon \fIinterface\fR" +Synonymous with the +.B ifname +modifier. +.IP "\fBrnr \fInum\fR" +True if the packet was logged as matching the specified PF rule number +(applies only to packets logged by OpenBSD's +.BR pf (4)). +.IP "\fBrulenum \fInum\fR" +Synonomous with the +.B rnr +modifier. +.IP "\fBreason \fIcode\fR" +True if the packet was logged with the specified PF reason code. The known +codes are: +.BR match , +.BR bad-offset , +.BR fragment , +.BR short , +.BR normalize , +and +.B memory +(applies only to packets logged by OpenBSD's +.BR pf (4)). +.IP "\fBrset \fIname\fR" +True if the packet was logged as matching the specified PF ruleset +name of an anchored ruleset (applies only to packets logged by +.BR pf (4)). +.IP "\fBruleset \fIname\fR" +Synonomous with the +.B rset +modifier. +.IP "\fBsrnr \fInum\fR" +True if the packet was logged as matching the specified PF rule number +of an anchored ruleset (applies only to packets logged by +.BR pf (4)). +.IP "\fBsubrulenum \fInum\fR" +Synonomous with the +.B srnr +modifier. +.IP "\fBaction \fIact\fR" +True if PF took the specified action when the packet was logged. Known actions +are: +.B pass +and +.B block +(applies only to packets logged by OpenBSD's +.BR pf (4)). +.IP "\fBip\fR, \fBip6\fR, \fBarp\fR, \fBrarp\fR, \fBatalk\fR, \fBaarp\fR, \fBdecnet\fR, \fBiso\fR, \fBstp\fR, \fBipx\fR, \fInetbeui\fP" +Abbreviations for: +.in +.5i +.nf +\fBether proto \fIp\fR +.fi +.in -.5i +where \fIp\fR is one of the above protocols. +.IP "\fBlat\fR, \fBmoprc\fR, \fBmopdl\fR" +Abbreviations for: +.in +.5i +.nf +\fBether proto \fIp\fR +.fi +.in -.5i +where \fIp\fR is one of the above protocols. +Note that +\fItcpdump\fP does not currently know how to parse these protocols. +.IP "\fBvlan \fI[vlan_id]\fR" +True if the packet is an IEEE 802.1Q VLAN packet. +If \fI[vlan_id]\fR is specified, only true if the packet has the specified +\fIvlan_id\fR. +Note that the first \fBvlan\fR keyword encountered in \fIexpression\fR +changes the decoding offsets for the remainder of \fIexpression\fR on +the assumption that the packet is a VLAN packet. The \fBvlan +\fI[vlan_id]\fR expression may be used more than once, to filter on VLAN +hierarchies. Each use of that expression increments the filter offsets +by 4. +.IP +For example: +.in +.5i +.nf +\fBvlan 100 && vlan 200\fR +.fi +.in -.5i +filters on VLAN 200 encapsulated within VLAN 100, and +.in +.5i +.nf +\fBvlan && vlan 300 && ip\fR +.fi +.in -.5i +filters IPv4 protocols encapsulated in VLAN 300 encapsulated within any +higher order VLAN. +.IP "\fBmpls \fI[label_num]\fR" +True if the packet is an MPLS packet. +If \fI[label_num]\fR is specified, only true is the packet has the specified +\fIlabel_num\fR. +Note that the first \fBmpls\fR keyword encountered in \fIexpression\fR +changes the decoding offsets for the remainder of \fIexpression\fR on +the assumption that the packet is a MPLS-encapsulated IP packet. The +\fBmpls \fI[label_num]\fR expression may be used more than once, to +filter on MPLS hierarchies. Each use of that expression increments the +filter offsets by 4. +.IP +For example: +.in +.5i +.nf +\fBmpls 100000 && mpls 1024\fR +.fi +.in -.5i +filters packets with an outer label of 100000 and an inner label of +1024, and +.in +.5i +.nf +\fBmpls && mpls 1024 && host 192.9.200.1\fR +.fi +.in -.5i +filters packets to or from 192.9.200.1 with an inner label of 1024 and +any outer label. +.IP \fBpppoed\fP +True if the packet is a PPP-over-Ethernet Discovery packet (Ethernet +type 0x8863). +.IP \fBpppoes\fP +True if the packet is a PPP-over-Ethernet Session packet (Ethernet +type 0x8864). +Note that the first \fBpppoes\fR keyword encountered in \fIexpression\fR +changes the decoding offsets for the remainder of \fIexpression\fR on +the assumption that the packet is a PPPoE session packet. +.IP +For example: +.in +.5i +.nf +\fBpppoes && ip\fR +.fi +.in -.5i +filters IPv4 protocols encapsulated in PPPoE. +.IP "\fBtcp\fR, \fBudp\fR, \fBicmp\fR" +Abbreviations for: +.in +.5i +.nf +\fBip proto \fIp\fR\fB or ip6 proto \fIp\fR +.fi +.in -.5i +where \fIp\fR is one of the above protocols. +.IP "\fBiso proto \fIprotocol\fR" +True if the packet is an OSI packet of protocol type \fIprotocol\fP. +\fIProtocol\fP can be a number or one of the names +\fBclnp\fP, \fBesis\fP, or \fBisis\fP. +.IP "\fBclnp\fR, \fBesis\fR, \fBisis\fR" +Abbreviations for: +.in +.5i +.nf +\fBiso proto \fIp\fR +.fi +.in -.5i +where \fIp\fR is one of the above protocols. +.IP "\fBl1\fR, \fBl2\fR, \fBiih\fR, \fBlsp\fR, \fBsnp\fR, \fBcsnp\fR, \fBpsnp\fR" +Abbreviations for IS-IS PDU types. +.IP "\fBvpi\fP \fIn\fR +True if the packet is an ATM packet, for SunATM on Solaris, with a +virtual path identifier of +.IR n . +.IP "\fBvci\fP \fIn\fR +True if the packet is an ATM packet, for SunATM on Solaris, with a +virtual channel identifier of +.IR n . +.IP \fBlane\fP +True if the packet is an ATM packet, for SunATM on Solaris, and is +an ATM LANE packet. +Note that the first \fBlane\fR keyword encountered in \fIexpression\fR +changes the tests done in the remainder of \fIexpression\fR +on the assumption that the packet is either a LANE emulated Ethernet +packet or a LANE LE Control packet. If \fBlane\fR isn't specified, the +tests are done under the assumption that the packet is an +LLC-encapsulated packet. +.IP \fBllc\fP +True if the packet is an ATM packet, for SunATM on Solaris, and is +an LLC-encapsulated packet. +.IP \fBoamf4s\fP +True if the packet is an ATM packet, for SunATM on Solaris, and is +a segment OAM F4 flow cell (VPI=0 & VCI=3). +.IP \fBoamf4e\fP +True if the packet is an ATM packet, for SunATM on Solaris, and is +an end-to-end OAM F4 flow cell (VPI=0 & VCI=4). +.IP \fBoamf4\fP +True if the packet is an ATM packet, for SunATM on Solaris, and is +a segment or end-to-end OAM F4 flow cell (VPI=0 & (VCI=3 | VCI=4)). +.IP \fBoam\fP +True if the packet is an ATM packet, for SunATM on Solaris, and is +a segment or end-to-end OAM F4 flow cell (VPI=0 & (VCI=3 | VCI=4)). +.IP \fBmetac\fP +True if the packet is an ATM packet, for SunATM on Solaris, and is +on a meta signaling circuit (VPI=0 & VCI=1). +.IP \fBbcc\fP +True if the packet is an ATM packet, for SunATM on Solaris, and is +on a broadcast signaling circuit (VPI=0 & VCI=2). +.IP \fBsc\fP +True if the packet is an ATM packet, for SunATM on Solaris, and is +on a signaling circuit (VPI=0 & VCI=5). +.IP \fBilmic\fP +True if the packet is an ATM packet, for SunATM on Solaris, and is +on an ILMI circuit (VPI=0 & VCI=16). +.IP \fBconnectmsg\fP +True if the packet is an ATM packet, for SunATM on Solaris, and is +on a signaling circuit and is a Q.2931 Setup, Call Proceeding, Connect, +Connect Ack, Release, or Release Done message. +.IP \fBmetaconnect\fP +True if the packet is an ATM packet, for SunATM on Solaris, and is +on a meta signaling circuit and is a Q.2931 Setup, Call Proceeding, Connect, +Release, or Release Done message. +.IP "\fIexpr relop expr\fR" +True if the relation holds, where \fIrelop\fR is one of >, <, >=, <=, =, +!=, and \fIexpr\fR is an arithmetic expression composed of integer +constants (expressed in standard C syntax), the normal binary operators +[+, -, *, /, &, |, <<, >>], a length operator, and special packet data +accessors. Note that all comparisons are unsigned, so that, for example, +0x80000000 and 0xffffffff are > 0. +To access +data inside the packet, use the following syntax: +.in +.5i +.nf +\fIproto\fB [ \fIexpr\fB : \fIsize\fB ]\fR +.fi +.in -.5i +\fIProto\fR is one of \fBether, fddi, tr, wlan, ppp, slip, link, +ip, arp, rarp, tcp, udp, icmp, ip6\fR or \fBradio\fR, and +indicates the protocol layer for the index operation. +(\fBether, fddi, wlan, tr, ppp, slip\fR and \fBlink\fR all refer to the +link layer. \fBradio\fR refers to the "radio header" added to some +802.11 captures.) +Note that \fItcp, udp\fR and other upper-layer protocol types only +apply to IPv4, not IPv6 (this will be fixed in the future). +The byte offset, relative to the indicated protocol layer, is +given by \fIexpr\fR. +\fISize\fR is optional and indicates the number of bytes in the +field of interest; it can be either one, two, or four, and defaults to one. +The length operator, indicated by the keyword \fBlen\fP, gives the +length of the packet. + +For example, `\fBether[0] & 1 != 0\fP' catches all multicast traffic. +The expression `\fBip[0] & 0xf != 5\fP' +catches all IPv4 packets with options. +The expression +`\fBip[6:2] & 0x1fff = 0\fP' +catches only unfragmented IPv4 datagrams and frag zero of fragmented +IPv4 datagrams. +This check is implicitly applied to the \fBtcp\fP and \fBudp\fP +index operations. +For instance, \fBtcp[0]\fP always means the first +byte of the TCP \fIheader\fP, and never means the first byte of an +intervening fragment. + +Some offsets and field values may be expressed as names rather than +as numeric values. +The following protocol header field offsets are +available: \fBicmptype\fP (ICMP type field), \fBicmpcode\fP (ICMP +code field), and \fBtcpflags\fP (TCP flags field). + +The following ICMP type field values are available: \fBicmp-echoreply\fP, +\fBicmp-unreach\fP, \fBicmp-sourcequench\fP, \fBicmp-redirect\fP, +\fBicmp-echo\fP, \fBicmp-routeradvert\fP, \fBicmp-routersolicit\fP, +\fBicmp-timxceed\fP, \fBicmp-paramprob\fP, \fBicmp-tstamp\fP, +\fBicmp-tstampreply\fP, \fBicmp-ireq\fP, \fBicmp-ireqreply\fP, +\fBicmp-maskreq\fP, \fBicmp-maskreply\fP. + +The following TCP flags field values are available: \fBtcp-fin\fP, +\fBtcp-syn\fP, \fBtcp-rst\fP, \fBtcp-push\fP, +\fBtcp-ack\fP, \fBtcp-urg\fP. +.LP +Primitives may be combined using: +.IP +A parenthesized group of primitives and operators +(parentheses are special to the Shell and must be escaped). +.IP +Negation (`\fB!\fP' or `\fBnot\fP'). +.IP +Concatenation (`\fB&&\fP' or `\fBand\fP'). +.IP +Alternation (`\fB||\fP' or `\fBor\fP'). +.LP +Negation has highest precedence. +Alternation and concatenation have equal precedence and associate +left to right. +Note that explicit \fBand\fR tokens, not juxtaposition, +are now required for concatenation. +.LP +If an identifier is given without a keyword, the most recent keyword +is assumed. +For example, +.in +.5i +.nf +\fBnot host vs and ace\fR +.fi +.in -.5i +is short for +.in +.5i +.nf +\fBnot host vs and host ace\fR +.fi +.in -.5i +which should not be confused with +.in +.5i +.nf +\fBnot ( host vs or ace )\fR +.fi +.in -.5i +.LP +Expression arguments can be passed to \fItcpdump\fP as either a single +argument or as multiple arguments, whichever is more convenient. +Generally, if the expression contains Shell metacharacters, it is +easier to pass it as a single, quoted argument. +Multiple arguments are concatenated with spaces before being parsed. +.SH EXAMPLES +.LP +To print all packets arriving at or departing from \fIsundown\fP: +.RS +.nf +\fBtcpdump host sundown\fP +.fi +.RE +.LP +To print traffic between \fIhelios\fR and either \fIhot\fR or \fIace\fR: +.RS +.nf +\fBtcpdump host helios and \\( hot or ace \\)\fP +.fi +.RE +.LP +To print all IP packets between \fIace\fR and any host except \fIhelios\fR: +.RS +.nf +\fBtcpdump ip host ace and not helios\fP +.fi +.RE +.LP +To print all traffic between local hosts and hosts at Berkeley: +.RS +.nf +.B +tcpdump net ucb-ether +.fi +.RE +.LP +To print all ftp traffic through internet gateway \fIsnup\fP: +(note that the expression is quoted to prevent the shell from +(mis-)interpreting the parentheses): +.RS +.nf +.B +tcpdump 'gateway snup and (port ftp or ftp-data)' +.fi +.RE +.LP +To print traffic neither sourced from nor destined for local hosts +(if you gateway to one other net, this stuff should never make it +onto your local net). +.RS +.nf +.B +tcpdump ip and not net \fIlocalnet\fP +.fi +.RE +.LP +To print the start and end packets (the SYN and FIN packets) of each +TCP conversation that involves a non-local host. +.RS +.nf +.B +tcpdump 'tcp[tcpflags] & (tcp-syn|tcp-fin) != 0 and not src and dst net \fIlocalnet\fP' +.fi +.RE +.LP +To print all IPv4 HTTP packets to and from port 80, i.e. print only +packets that contain data, not, for example, SYN and FIN packets and +ACK-only packets. (IPv6 is left as an exercise for the reader.) +.RS +.nf +.B +tcpdump 'tcp port 80 and (((ip[2:2] - ((ip[0]&0xf)<<2)) - ((tcp[12]&0xf0)>>2)) != 0)' +.fi +.RE +.LP +To print IP packets longer than 576 bytes sent through gateway \fIsnup\fP: +.RS +.nf +.B +tcpdump 'gateway snup and ip[2:2] > 576' +.fi +.RE +.LP +To print IP broadcast or multicast packets that were +.I not +sent via Ethernet broadcast or multicast: +.RS +.nf +.B +tcpdump 'ether[0] & 1 = 0 and ip[16] >= 224' +.fi +.RE +.LP +To print all ICMP packets that are not echo requests/replies (i.e., not +ping packets): +.RS +.nf +.B +tcpdump 'icmp[icmptype] != icmp-echo and icmp[icmptype] != icmp-echoreply' +.fi +.RE +.SH OUTPUT FORMAT +.LP +The output of \fItcpdump\fP is protocol dependent. +The following +gives a brief description and examples of most of the formats. +.de HD +.sp 1.5 +.B +.. +.HD +Link Level Headers +.LP +If the '-e' option is given, the link level header is printed out. +On Ethernets, the source and destination addresses, protocol, +and packet length are printed. +.LP +On FDDI networks, the '-e' option causes \fItcpdump\fP to print +the `frame control' field, the source and destination addresses, +and the packet length. +(The `frame control' field governs the +interpretation of the rest of the packet. +Normal packets (such +as those containing IP datagrams) are `async' packets, with a priority +value between 0 and 7; for example, `\fBasync4\fR'. +Such packets +are assumed to contain an 802.2 Logical Link Control (LLC) packet; +the LLC header is printed if it is \fInot\fR an ISO datagram or a +so-called SNAP packet. +.LP +On Token Ring networks, the '-e' option causes \fItcpdump\fP to print +the `access control' and `frame control' fields, the source and +destination addresses, and the packet length. +As on FDDI networks, +packets are assumed to contain an LLC packet. +Regardless of whether +the '-e' option is specified or not, the source routing information is +printed for source-routed packets. +.LP +On 802.11 networks, the '-e' option causes \fItcpdump\fP to print +the `frame control' fields, all of the addresses in the 802.11 header, +and the packet length. +As on FDDI networks, +packets are assumed to contain an LLC packet. +.LP +\fI(N.B.: The following description assumes familiarity with +the SLIP compression algorithm described in RFC-1144.)\fP +.LP +On SLIP links, a direction indicator (``I'' for inbound, ``O'' for outbound), +packet type, and compression information are printed out. +The packet type is printed first. +The three types are \fIip\fP, \fIutcp\fP, and \fIctcp\fP. +No further link information is printed for \fIip\fR packets. +For TCP packets, the connection identifier is printed following the type. +If the packet is compressed, its encoded header is printed out. +The special cases are printed out as +\fB*S+\fIn\fR and \fB*SA+\fIn\fR, where \fIn\fR is the amount by which +the sequence number (or sequence number and ack) has changed. +If it is not a special case, +zero or more changes are printed. +A change is indicated by U (urgent pointer), W (window), A (ack), +S (sequence number), and I (packet ID), followed by a delta (+n or -n), +or a new value (=n). +Finally, the amount of data in the packet and compressed header length +are printed. +.LP +For example, the following line shows an outbound compressed TCP packet, +with an implicit connection identifier; the ack has changed by 6, +the sequence number by 49, and the packet ID by 6; there are 3 bytes of +data and 6 bytes of compressed header: +.RS +.nf +\fBO ctcp * A+6 S+49 I+6 3 (6)\fP +.fi +.RE +.HD +ARP/RARP Packets +.LP +Arp/rarp output shows the type of request and its arguments. +The +format is intended to be self explanatory. +Here is a short sample taken from the start of an `rlogin' from +host \fIrtsg\fP to host \fIcsam\fP: +.RS +.nf +.sp .5 +\f(CWarp who-has csam tell rtsg +arp reply csam is-at CSAM\fR +.sp .5 +.fi +.RE +The first line says that rtsg sent an arp packet asking +for the Ethernet address of internet host csam. +Csam +replies with its Ethernet address (in this example, Ethernet addresses +are in caps and internet addresses in lower case). +.LP +This would look less redundant if we had done \fItcpdump \-n\fP: +.RS +.nf +.sp .5 +\f(CWarp who-has 128.3.254.6 tell 128.3.254.68 +arp reply 128.3.254.6 is-at 02:07:01:00:01:c4\fP +.fi +.RE +.LP +If we had done \fItcpdump \-e\fP, the fact that the first packet is +broadcast and the second is point-to-point would be visible: +.RS +.nf +.sp .5 +\f(CWRTSG Broadcast 0806 64: arp who-has csam tell rtsg +CSAM RTSG 0806 64: arp reply csam is-at CSAM\fR +.sp .5 +.fi +.RE +For the first packet this says the Ethernet source address is RTSG, the +destination is the Ethernet broadcast address, the type field +contained hex 0806 (type ETHER_ARP) and the total length was 64 bytes. +.HD +TCP Packets +.LP +\fI(N.B.:The following description assumes familiarity with +the TCP protocol described in RFC-793. +If you are not familiar +with the protocol, neither this description nor \fItcpdump\fP will +be of much use to you.)\fP +.LP +The general format of a tcp protocol line is: +.RS +.nf +.sp .5 +\fIsrc > dst: flags data-seqno ack window urgent options\fP +.sp .5 +.fi +.RE +\fISrc\fP and \fIdst\fP are the source and destination IP +addresses and ports. +\fIFlags\fP are some combination of S (SYN), +F (FIN), P (PUSH), R (RST), W (ECN CWR) or E (ECN-Echo), or a single +`.' (no flags). +\fIData-seqno\fP describes the portion of sequence space covered +by the data in this packet (see example below). +\fIAck\fP is sequence number of the next data expected the other +direction on this connection. +\fIWindow\fP is the number of bytes of receive buffer space available +the other direction on this connection. +\fIUrg\fP indicates there is `urgent' data in the packet. +\fIOptions\fP are tcp options enclosed in angle brackets (e.g., <mss 1024>). +.LP +\fISrc, dst\fP and \fIflags\fP are always present. +The other fields +depend on the contents of the packet's tcp protocol header and +are output only if appropriate. +.LP +Here is the opening portion of an rlogin from host \fIrtsg\fP to +host \fIcsam\fP. +.RS +.nf +.sp .5 +\s-2\f(CWrtsg.1023 > csam.login: S 768512:768512(0) win 4096 <mss 1024> +csam.login > rtsg.1023: S 947648:947648(0) ack 768513 win 4096 <mss 1024> +rtsg.1023 > csam.login: . ack 1 win 4096 +rtsg.1023 > csam.login: P 1:2(1) ack 1 win 4096 +csam.login > rtsg.1023: . ack 2 win 4096 +rtsg.1023 > csam.login: P 2:21(19) ack 1 win 4096 +csam.login > rtsg.1023: P 1:2(1) ack 21 win 4077 +csam.login > rtsg.1023: P 2:3(1) ack 21 win 4077 urg 1 +csam.login > rtsg.1023: P 3:4(1) ack 21 win 4077 urg 1\fR\s+2 +.sp .5 +.fi +.RE +The first line says that tcp port 1023 on rtsg sent a packet +to port \fIlogin\fP +on csam. +The \fBS\fP indicates that the \fISYN\fP flag was set. +The packet sequence number was 768512 and it contained no data. +(The notation is `first:last(nbytes)' which means `sequence +numbers \fIfirst\fP +up to but not including \fIlast\fP which is \fInbytes\fP bytes of user data'.) +There was no piggy-backed ack, the available receive window was 4096 +bytes and there was a max-segment-size option requesting an mss of +1024 bytes. +.LP +Csam replies with a similar packet except it includes a piggy-backed +ack for rtsg's SYN. +Rtsg then acks csam's SYN. +The `.' means no +flags were set. +The packet contained no data so there is no data sequence number. +Note that the ack sequence +number is a small integer (1). +The first time \fItcpdump\fP sees a +tcp `conversation', it prints the sequence number from the packet. +On subsequent packets of the conversation, the difference between +the current packet's sequence number and this initial sequence number +is printed. +This means that sequence numbers after the +first can be interpreted +as relative byte positions in the conversation's data stream (with the +first data byte each direction being `1'). +`-S' will override this +feature, causing the original sequence numbers to be output. +.LP +On the 6th line, rtsg sends csam 19 bytes of data (bytes 2 through 20 +in the rtsg \(-> csam side of the conversation). +The PUSH flag is set in the packet. +On the 7th line, csam says it's received data sent by rtsg up to +but not including byte 21. +Most of this data is apparently sitting in the +socket buffer since csam's receive window has gotten 19 bytes smaller. +Csam also sends one byte of data to rtsg in this packet. +On the 8th and 9th lines, +csam sends two bytes of urgent, pushed data to rtsg. +.LP +If the snapshot was small enough that \fItcpdump\fP didn't capture +the full TCP header, it interprets as much of the header as it can +and then reports ``[|\fItcp\fP]'' to indicate the remainder could not +be interpreted. +If the header contains a bogus option (one with a length +that's either too small or beyond the end of the header), \fItcpdump\fP +reports it as ``[\fIbad opt\fP]'' and does not interpret any further +options (since it's impossible to tell where they start). +If the header +length indicates options are present but the IP datagram length is not +long enough for the options to actually be there, \fItcpdump\fP reports +it as ``[\fIbad hdr length\fP]''. +.HD +.B Capturing TCP packets with particular flag combinations (SYN-ACK, URG-ACK, etc.) +.PP +There are 8 bits in the control bits section of the TCP header: +.IP +.I CWR | ECE | URG | ACK | PSH | RST | SYN | FIN +.PP +Let's assume that we want to watch packets used in establishing +a TCP connection. +Recall that TCP uses a 3-way handshake protocol +when it initializes a new connection; the connection sequence with +regard to the TCP control bits is +.PP +.RS +1) Caller sends SYN +.RE +.RS +2) Recipient responds with SYN, ACK +.RE +.RS +3) Caller sends ACK +.RE +.PP +Now we're interested in capturing packets that have only the +SYN bit set (Step 1). +Note that we don't want packets from step 2 +(SYN-ACK), just a plain initial SYN. +What we need is a correct filter +expression for \fItcpdump\fP. +.PP +Recall the structure of a TCP header without options: +.PP +.nf + 0 15 31 +----------------------------------------------------------------- +| source port | destination port | +----------------------------------------------------------------- +| sequence number | +----------------------------------------------------------------- +| acknowledgment number | +----------------------------------------------------------------- +| HL | rsvd |C|E|U|A|P|R|S|F| window size | +----------------------------------------------------------------- +| TCP checksum | urgent pointer | +----------------------------------------------------------------- +.fi +.PP +A TCP header usually holds 20 octets of data, unless options are +present. +The first line of the graph contains octets 0 - 3, the +second line shows octets 4 - 7 etc. +.PP +Starting to count with 0, the relevant TCP control bits are contained +in octet 13: +.PP +.nf + 0 7| 15| 23| 31 +----------------|---------------|---------------|---------------- +| HL | rsvd |C|E|U|A|P|R|S|F| window size | +----------------|---------------|---------------|---------------- +| | 13th octet | | | +.fi +.PP +Let's have a closer look at octet no. 13: +.PP +.nf + | | + |---------------| + |C|E|U|A|P|R|S|F| + |---------------| + |7 5 3 0| +.fi +.PP +These are the TCP control bits we are interested +in. +We have numbered the bits in this octet from 0 to 7, right to +left, so the PSH bit is bit number 3, while the URG bit is number 5. +.PP +Recall that we want to capture packets with only SYN set. +Let's see what happens to octet 13 if a TCP datagram arrives +with the SYN bit set in its header: +.PP +.nf + |C|E|U|A|P|R|S|F| + |---------------| + |0 0 0 0 0 0 1 0| + |---------------| + |7 6 5 4 3 2 1 0| +.fi +.PP +Looking at the +control bits section we see that only bit number 1 (SYN) is set. +.PP +Assuming that octet number 13 is an 8-bit unsigned integer in +network byte order, the binary value of this octet is +.IP +00000010 +.PP +and its decimal representation is +.PP +.nf + 7 6 5 4 3 2 1 0 +0*2 + 0*2 + 0*2 + 0*2 + 0*2 + 0*2 + 1*2 + 0*2 = 2 +.fi +.PP +We're almost done, because now we know that if only SYN is set, +the value of the 13th octet in the TCP header, when interpreted +as a 8-bit unsigned integer in network byte order, must be exactly 2. +.PP +This relationship can be expressed as +.RS +.B +tcp[13] == 2 +.RE +.PP +We can use this expression as the filter for \fItcpdump\fP in order +to watch packets which have only SYN set: +.RS +.B +tcpdump -i xl0 tcp[13] == 2 +.RE +.PP +The expression says "let the 13th octet of a TCP datagram have +the decimal value 2", which is exactly what we want. +.PP +Now, let's assume that we need to capture SYN packets, but we +don't care if ACK or any other TCP control bit is set at the +same time. +Let's see what happens to octet 13 when a TCP datagram +with SYN-ACK set arrives: +.PP +.nf + |C|E|U|A|P|R|S|F| + |---------------| + |0 0 0 1 0 0 1 0| + |---------------| + |7 6 5 4 3 2 1 0| +.fi +.PP +Now bits 1 and 4 are set in the 13th octet. +The binary value of +octet 13 is +.IP + 00010010 +.PP +which translates to decimal +.PP +.nf + 7 6 5 4 3 2 1 0 +0*2 + 0*2 + 0*2 + 1*2 + 0*2 + 0*2 + 1*2 + 0*2 = 18 +.fi +.PP +Now we can't just use 'tcp[13] == 18' in the \fItcpdump\fP filter +expression, because that would select only those packets that have +SYN-ACK set, but not those with only SYN set. +Remember that we don't care +if ACK or any other control bit is set as long as SYN is set. +.PP +In order to achieve our goal, we need to logically AND the +binary value of octet 13 with some other value to preserve +the SYN bit. +We know that we want SYN to be set in any case, +so we'll logically AND the value in the 13th octet with +the binary value of a SYN: +.PP +.nf + + 00010010 SYN-ACK 00000010 SYN + AND 00000010 (we want SYN) AND 00000010 (we want SYN) + -------- -------- + = 00000010 = 00000010 +.fi +.PP +We see that this AND operation delivers the same result +regardless whether ACK or another TCP control bit is set. +The decimal representation of the AND value as well as +the result of this operation is 2 (binary 00000010), +so we know that for packets with SYN set the following +relation must hold true: +.IP +( ( value of octet 13 ) AND ( 2 ) ) == ( 2 ) +.PP +This points us to the \fItcpdump\fP filter expression +.RS +.B + tcpdump -i xl0 'tcp[13] & 2 == 2' +.RE +.PP +Note that you should use single quotes or a backslash +in the expression to hide the AND ('&') special character +from the shell. +.HD +.B +UDP Packets +.LP +UDP format is illustrated by this rwho packet: +.RS +.nf +.sp .5 +\f(CWactinide.who > broadcast.who: udp 84\fP +.sp .5 +.fi +.RE +This says that port \fIwho\fP on host \fIactinide\fP sent a udp +datagram to port \fIwho\fP on host \fIbroadcast\fP, the Internet +broadcast address. +The packet contained 84 bytes of user data. +.LP +Some UDP services are recognized (from the source or destination +port number) and the higher level protocol information printed. +In particular, Domain Name service requests (RFC-1034/1035) and Sun +RPC calls (RFC-1050) to NFS. +.HD +UDP Name Server Requests +.LP +\fI(N.B.:The following description assumes familiarity with +the Domain Service protocol described in RFC-1035. +If you are not familiar +with the protocol, the following description will appear to be written +in greek.)\fP +.LP +Name server requests are formatted as +.RS +.nf +.sp .5 +\fIsrc > dst: id op? flags qtype qclass name (len)\fP +.sp .5 +\f(CWh2opolo.1538 > helios.domain: 3+ A? ucbvax.berkeley.edu. (37)\fR +.sp .5 +.fi +.RE +Host \fIh2opolo\fP asked the domain server on \fIhelios\fP for an +address record (qtype=A) associated with the name \fIucbvax.berkeley.edu.\fP +The query id was `3'. +The `+' indicates the \fIrecursion desired\fP flag +was set. +The query length was 37 bytes, not including the UDP and +IP protocol headers. +The query operation was the normal one, \fIQuery\fP, +so the op field was omitted. +If the op had been anything else, it would +have been printed between the `3' and the `+'. +Similarly, the qclass was the normal one, +\fIC_IN\fP, and omitted. +Any other qclass would have been printed +immediately after the `A'. +.LP +A few anomalies are checked and may result in extra fields enclosed in +square brackets: If a query contains an answer, authority records or +additional records section, +.IR ancount , +.IR nscount , +or +.I arcount +are printed as `[\fIn\fPa]', `[\fIn\fPn]' or `[\fIn\fPau]' where \fIn\fP +is the appropriate count. +If any of the response bits are set (AA, RA or rcode) or any of the +`must be zero' bits are set in bytes two and three, `[b2&3=\fIx\fP]' +is printed, where \fIx\fP is the hex value of header bytes two and three. +.HD +UDP Name Server Responses +.LP +Name server responses are formatted as +.RS +.nf +.sp .5 +\fIsrc > dst: id op rcode flags a/n/au type class data (len)\fP +.sp .5 +\f(CWhelios.domain > h2opolo.1538: 3 3/3/7 A 128.32.137.3 (273) +helios.domain > h2opolo.1537: 2 NXDomain* 0/1/0 (97)\fR +.sp .5 +.fi +.RE +In the first example, \fIhelios\fP responds to query id 3 from \fIh2opolo\fP +with 3 answer records, 3 name server records and 7 additional records. +The first answer record is type A (address) and its data is internet +address 128.32.137.3. +The total size of the response was 273 bytes, +excluding UDP and IP headers. +The op (Query) and response code +(NoError) were omitted, as was the class (C_IN) of the A record. +.LP +In the second example, \fIhelios\fP responds to query 2 with a +response code of non-existent domain (NXDomain) with no answers, +one name server and no authority records. +The `*' indicates that +the \fIauthoritative answer\fP bit was set. +Since there were no +answers, no type, class or data were printed. +.LP +Other flag characters that might appear are `\-' (recursion available, +RA, \fInot\fP set) and `|' (truncated message, TC, set). +If the +`question' section doesn't contain exactly one entry, `[\fIn\fPq]' +is printed. +.LP +Note that name server requests and responses tend to be large and the +default \fIsnaplen\fP of 68 bytes may not capture enough of the packet +to print. +Use the \fB\-s\fP flag to increase the snaplen if you +need to seriously investigate name server traffic. +`\fB\-s 128\fP' +has worked well for me. + +.HD +SMB/CIFS decoding +.LP +\fItcpdump\fP now includes fairly extensive SMB/CIFS/NBT decoding for data +on UDP/137, UDP/138 and TCP/139. +Some primitive decoding of IPX and +NetBEUI SMB data is also done. + +By default a fairly minimal decode is done, with a much more detailed +decode done if -v is used. +Be warned that with -v a single SMB packet +may take up a page or more, so only use -v if you really want all the +gory details. + +For information on SMB packet formats and what all te fields mean see +www.cifs.org or the pub/samba/specs/ directory on your favorite +samba.org mirror site. +The SMB patches were written by Andrew Tridgell +(tridge@samba.org). + +.HD +NFS Requests and Replies +.LP +Sun NFS (Network File System) requests and replies are printed as: +.RS +.nf +.sp .5 +\fIsrc.xid > dst.nfs: len op args\fP +\fIsrc.nfs > dst.xid: reply stat len op results\fP +.sp .5 +\f(CW +sushi.6709 > wrl.nfs: 112 readlink fh 21,24/10.73165 +wrl.nfs > sushi.6709: reply ok 40 readlink "../var" +sushi.201b > wrl.nfs: + 144 lookup fh 9,74/4096.6878 "xcolors" +wrl.nfs > sushi.201b: + reply ok 128 lookup fh 9,74/4134.3150 +\fR +.sp .5 +.fi +.RE +In the first line, host \fIsushi\fP sends a transaction with id \fI6709\fP +to \fIwrl\fP (note that the number following the src host is a +transaction id, \fInot\fP the source port). +The request was 112 bytes, +excluding the UDP and IP headers. +The operation was a \fIreadlink\fP +(read symbolic link) on file handle (\fIfh\fP) 21,24/10.731657119. +(If one is lucky, as in this case, the file handle can be interpreted +as a major,minor device number pair, followed by the inode number and +generation number.) +\fIWrl\fP replies `ok' with the contents of the link. +.LP +In the third line, \fIsushi\fP asks \fIwrl\fP to lookup the name +`\fIxcolors\fP' in directory file 9,74/4096.6878. +Note that the data printed +depends on the operation type. +The format is intended to be self +explanatory if read in conjunction with +an NFS protocol spec. +.LP +If the \-v (verbose) flag is given, additional information is printed. +For example: +.RS +.nf +.sp .5 +\f(CW +sushi.1372a > wrl.nfs: + 148 read fh 21,11/12.195 8192 bytes @ 24576 +wrl.nfs > sushi.1372a: + reply ok 1472 read REG 100664 ids 417/0 sz 29388 +\fP +.sp .5 +.fi +.RE +(\-v also prints the IP header TTL, ID, length, and fragmentation fields, +which have been omitted from this example.) In the first line, +\fIsushi\fP asks \fIwrl\fP to read 8192 bytes from file 21,11/12.195, +at byte offset 24576. +\fIWrl\fP replies `ok'; the packet shown on the +second line is the first fragment of the reply, and hence is only 1472 +bytes long (the other bytes will follow in subsequent fragments, but +these fragments do not have NFS or even UDP headers and so might not be +printed, depending on the filter expression used). +Because the \-v flag +is given, some of the file attributes (which are returned in addition +to the file data) are printed: the file type (``REG'', for regular file), +the file mode (in octal), the uid and gid, and the file size. +.LP +If the \-v flag is given more than once, even more details are printed. +.LP +Note that NFS requests are very large and much of the detail won't be printed +unless \fIsnaplen\fP is increased. +Try using `\fB\-s 192\fP' to watch +NFS traffic. +.LP +NFS reply packets do not explicitly identify the RPC operation. +Instead, +\fItcpdump\fP keeps track of ``recent'' requests, and matches them to the +replies using the transaction ID. +If a reply does not closely follow the +corresponding request, it might not be parsable. +.HD +AFS Requests and Replies +.LP +Transarc AFS (Andrew File System) requests and replies are printed +as: +.HD +.RS +.nf +.sp .5 +\fIsrc.sport > dst.dport: rx packet-type\fP +\fIsrc.sport > dst.dport: rx packet-type service call call-name args\fP +\fIsrc.sport > dst.dport: rx packet-type service reply call-name args\fP +.sp .5 +\f(CW +elvis.7001 > pike.afsfs: + rx data fs call rename old fid 536876964/1/1 ".newsrc.new" + new fid 536876964/1/1 ".newsrc" +pike.afsfs > elvis.7001: rx data fs reply rename +\fR +.sp .5 +.fi +.RE +In the first line, host elvis sends a RX packet to pike. +This was +a RX data packet to the fs (fileserver) service, and is the start of +an RPC call. +The RPC call was a rename, with the old directory file id +of 536876964/1/1 and an old filename of `.newsrc.new', and a new directory +file id of 536876964/1/1 and a new filename of `.newsrc'. +The host pike +responds with a RPC reply to the rename call (which was successful, because +it was a data packet and not an abort packet). +.LP +In general, all AFS RPCs are decoded at least by RPC call name. +Most +AFS RPCs have at least some of the arguments decoded (generally only +the `interesting' arguments, for some definition of interesting). +.LP +The format is intended to be self-describing, but it will probably +not be useful to people who are not familiar with the workings of +AFS and RX. +.LP +If the -v (verbose) flag is given twice, acknowledgement packets and +additional header information is printed, such as the the RX call ID, +call number, sequence number, serial number, and the RX packet flags. +.LP +If the -v flag is given twice, additional information is printed, +such as the the RX call ID, serial number, and the RX packet flags. +The MTU negotiation information is also printed from RX ack packets. +.LP +If the -v flag is given three times, the security index and service id +are printed. +.LP +Error codes are printed for abort packets, with the exception of Ubik +beacon packets (because abort packets are used to signify a yes vote +for the Ubik protocol). +.LP +Note that AFS requests are very large and many of the arguments won't +be printed unless \fIsnaplen\fP is increased. +Try using `\fB-s 256\fP' +to watch AFS traffic. +.LP +AFS reply packets do not explicitly identify the RPC operation. +Instead, +\fItcpdump\fP keeps track of ``recent'' requests, and matches them to the +replies using the call number and service ID. +If a reply does not closely +follow the +corresponding request, it might not be parsable. + +.HD +KIP AppleTalk (DDP in UDP) +.LP +AppleTalk DDP packets encapsulated in UDP datagrams are de-encapsulated +and dumped as DDP packets (i.e., all the UDP header information is +discarded). +The file +.I /etc/atalk.names +is used to translate AppleTalk net and node numbers to names. +Lines in this file have the form +.RS +.nf +.sp .5 +\fInumber name\fP + +\f(CW1.254 ether +16.1 icsd-net +1.254.110 ace\fR +.sp .5 +.fi +.RE +The first two lines give the names of AppleTalk networks. +The third +line gives the name of a particular host (a host is distinguished +from a net by the 3rd octet in the number \- +a net number \fImust\fP have two octets and a host number \fImust\fP +have three octets.) The number and name should be separated by +whitespace (blanks or tabs). +The +.I /etc/atalk.names +file may contain blank lines or comment lines (lines starting with +a `#'). +.LP +AppleTalk addresses are printed in the form +.RS +.nf +.sp .5 +\fInet.host.port\fP + +\f(CW144.1.209.2 > icsd-net.112.220 +office.2 > icsd-net.112.220 +jssmag.149.235 > icsd-net.2\fR +.sp .5 +.fi +.RE +(If the +.I /etc/atalk.names +doesn't exist or doesn't contain an entry for some AppleTalk +host/net number, addresses are printed in numeric form.) +In the first example, NBP (DDP port 2) on net 144.1 node 209 +is sending to whatever is listening on port 220 of net icsd node 112. +The second line is the same except the full name of the source node +is known (`office'). +The third line is a send from port 235 on +net jssmag node 149 to broadcast on the icsd-net NBP port (note that +the broadcast address (255) is indicated by a net name with no host +number \- for this reason it's a good idea to keep node names and +net names distinct in /etc/atalk.names). +.LP +NBP (name binding protocol) and ATP (AppleTalk transaction protocol) +packets have their contents interpreted. +Other protocols just dump +the protocol name (or number if no name is registered for the +protocol) and packet size. + +\fBNBP packets\fP are formatted like the following examples: +.RS +.nf +.sp .5 +\s-2\f(CWicsd-net.112.220 > jssmag.2: nbp-lkup 190: "=:LaserWriter@*" +jssmag.209.2 > icsd-net.112.220: nbp-reply 190: "RM1140:LaserWriter@*" 250 +techpit.2 > icsd-net.112.220: nbp-reply 190: "techpit:LaserWriter@*" 186\fR\s+2 +.sp .5 +.fi +.RE +The first line is a name lookup request for laserwriters sent by net icsd host +112 and broadcast on net jssmag. +The nbp id for the lookup is 190. +The second line shows a reply for this request (note that it has the +same id) from host jssmag.209 saying that it has a laserwriter +resource named "RM1140" registered on port 250. +The third line is +another reply to the same request saying host techpit has laserwriter +"techpit" registered on port 186. + +\fBATP packet\fP formatting is demonstrated by the following example: +.RS +.nf +.sp .5 +\s-2\f(CWjssmag.209.165 > helios.132: atp-req 12266<0-7> 0xae030001 +helios.132 > jssmag.209.165: atp-resp 12266:0 (512) 0xae040000 +helios.132 > jssmag.209.165: atp-resp 12266:1 (512) 0xae040000 +helios.132 > jssmag.209.165: atp-resp 12266:2 (512) 0xae040000 +helios.132 > jssmag.209.165: atp-resp 12266:3 (512) 0xae040000 +helios.132 > jssmag.209.165: atp-resp 12266:4 (512) 0xae040000 +helios.132 > jssmag.209.165: atp-resp 12266:5 (512) 0xae040000 +helios.132 > jssmag.209.165: atp-resp 12266:6 (512) 0xae040000 +helios.132 > jssmag.209.165: atp-resp*12266:7 (512) 0xae040000 +jssmag.209.165 > helios.132: atp-req 12266<3,5> 0xae030001 +helios.132 > jssmag.209.165: atp-resp 12266:3 (512) 0xae040000 +helios.132 > jssmag.209.165: atp-resp 12266:5 (512) 0xae040000 +jssmag.209.165 > helios.132: atp-rel 12266<0-7> 0xae030001 +jssmag.209.133 > helios.132: atp-req* 12267<0-7> 0xae030002\fR\s+2 +.sp .5 +.fi +.RE +Jssmag.209 initiates transaction id 12266 with host helios by requesting +up to 8 packets (the `<0-7>'). +The hex number at the end of the line +is the value of the `userdata' field in the request. +.LP +Helios responds with 8 512-byte packets. +The `:digit' following the +transaction id gives the packet sequence number in the transaction +and the number in parens is the amount of data in the packet, +excluding the atp header. +The `*' on packet 7 indicates that the +EOM bit was set. +.LP +Jssmag.209 then requests that packets 3 & 5 be retransmitted. +Helios +resends them then jssmag.209 releases the transaction. +Finally, +jssmag.209 initiates the next request. +The `*' on the request +indicates that XO (`exactly once') was \fInot\fP set. + +.HD +IP Fragmentation +.LP +Fragmented Internet datagrams are printed as +.RS +.nf +.sp .5 +\fB(frag \fIid\fB:\fIsize\fB@\fIoffset\fB+)\fR +\fB(frag \fIid\fB:\fIsize\fB@\fIoffset\fB)\fR +.sp .5 +.fi +.RE +(The first form indicates there are more fragments. +The second +indicates this is the last fragment.) +.LP +\fIId\fP is the fragment id. +\fISize\fP is the fragment +size (in bytes) excluding the IP header. +\fIOffset\fP is this +fragment's offset (in bytes) in the original datagram. +.LP +The fragment information is output for each fragment. +The first +fragment contains the higher level protocol header and the frag +info is printed after the protocol info. +Fragments +after the first contain no higher level protocol header and the +frag info is printed after the source and destination addresses. +For example, here is part of an ftp from arizona.edu to lbl-rtsg.arpa +over a CSNET connection that doesn't appear to handle 576 byte datagrams: +.RS +.nf +.sp .5 +\s-2\f(CWarizona.ftp-data > rtsg.1170: . 1024:1332(308) ack 1 win 4096 (frag 595a:328@0+) +arizona > rtsg: (frag 595a:204@328) +rtsg.1170 > arizona.ftp-data: . ack 1536 win 2560\fP\s+2 +.sp .5 +.fi +.RE +There are a couple of things to note here: First, addresses in the +2nd line don't include port numbers. +This is because the TCP +protocol information is all in the first fragment and we have no idea +what the port or sequence numbers are when we print the later fragments. +Second, the tcp sequence information in the first line is printed as if there +were 308 bytes of user data when, in fact, there are 512 bytes (308 in +the first frag and 204 in the second). +If you are looking for holes +in the sequence space or trying to match up acks +with packets, this can fool you. +.LP +A packet with the IP \fIdon't fragment\fP flag is marked with a +trailing \fB(DF)\fP. +.HD +Timestamps +.LP +By default, all output lines are preceded by a timestamp. +The timestamp +is the current clock time in the form +.RS +.nf +\fIhh:mm:ss.frac\fP +.fi +.RE +and is as accurate as the kernel's clock. +The timestamp reflects the time the kernel first saw the packet. +No attempt +is made to account for the time lag between when the +Ethernet interface removed the packet from the wire and when the kernel +serviced the `new packet' interrupt. +.SH "SEE ALSO" +bpf(4), pcap(3) +.SH AUTHORS +The original authors are: +.LP +Van Jacobson, +Craig Leres and +Steven McCanne, all of the +Lawrence Berkeley National Laboratory, University of California, Berkeley, CA. +.LP +It is currently being maintained by tcpdump.org. +.LP +The current version is available via http: +.LP +.RS +.I http://www.tcpdump.org/ +.RE +.LP +The original distribution is available via anonymous ftp: +.LP +.RS +.I ftp://ftp.ee.lbl.gov/tcpdump.tar.Z +.RE +.LP +IPv6/IPsec support is added by WIDE/KAME project. +This program uses Eric Young's SSLeay library, under specific configuration. +.SH BUGS +Please send problems, bugs, questions, desirable enhancements, etc. to: +.LP +.RS +tcpdump-workers@tcpdump.org +.RE +.LP +Please send source code contributions, etc. to: +.LP +.RS +patches@tcpdump.org +.RE +.LP +NIT doesn't let you watch your own outbound traffic, BPF will. +We recommend that you use the latter. +.LP +When running +.BR tcpdump +with the +.B \-v +option on a network interface supporting checksum off-loading, +IP packets sourced from this machine will have many false 'bad cksum 0' errors. +.LP +On Linux systems with 2.0[.x] kernels: +.IP +packets on the loopback device will be seen twice; +.IP +packet filtering cannot be done in the kernel, so that all packets must +be copied from the kernel in order to be filtered in user mode; +.IP +all of a packet, not just the part that's within the snapshot length, +will be copied from the kernel (the 2.0[.x] packet capture mechanism, if +asked to copy only part of a packet to userland, will not report the +true length of the packet; this would cause most IP packets to get an +error from +.BR tcpdump ); +.IP +capturing on some PPP devices won't work correctly. +.LP +We recommend that you upgrade to a 2.2 or later kernel. +.LP +Some attempt should be made to reassemble IP fragments or, at least +to compute the right length for the higher level protocol. +.LP +Name server inverse queries are not dumped correctly: the (empty) +question section is printed rather than real query in the answer +section. +Some believe that inverse queries are themselves a bug and +prefer to fix the program generating them rather than \fItcpdump\fP. +.LP +A packet trace that crosses a daylight savings time change will give +skewed time stamps (the time change is ignored). +.LP +Filter expressions on fields other than those in Token Ring headers will +not correctly handle source-routed Token Ring packets. +.LP +Filter expressions on fields other than those in 802.11 headers will not +correctly handle 802.11 data packets with both To DS and From DS set. +.LP +.BR "ip6 proto" +should chase header chain, but at this moment it does not. +.BR "ip6 protochain" +is supplied for this behavior. +.LP +Arithmetic expression against transport layer headers, like \fBtcp[0]\fP, +does not work against IPv6 packets. +It only looks at IPv4 packets. |
