diff options
Diffstat (limited to 'contrib/tcpdump/tcpdump.1')
| -rw-r--r-- | contrib/tcpdump/tcpdump.1 | 655 |
1 files changed, 457 insertions, 198 deletions
diff --git a/contrib/tcpdump/tcpdump.1 b/contrib/tcpdump/tcpdump.1 index 41f823a..7df9554 100644 --- a/contrib/tcpdump/tcpdump.1 +++ b/contrib/tcpdump/tcpdump.1 @@ -1,4 +1,4 @@ -.\" @(#) $Header: /tcpdump/master/tcpdump/tcpdump.1,v 1.92.2.3 2001/03/04 00:19:48 guy Exp $ (LBL) +.\" @(#) $Header: /tcpdump/master/tcpdump/tcpdump.1,v 1.114 2002/01/04 07:37:49 guy Exp $ (LBL) .\" .\" Copyright (c) 1987, 1988, 1989, 1990, 1991, 1992, 1994, 1995, 1996, 1997 .\" The Regents of the University of California. All rights reserved. @@ -27,10 +27,16 @@ tcpdump \- dump traffic on a network .na .B tcpdump [ -.B \-adeflnNOpqRStvxX +.B \-adeflnNOpqRStuvxX ] [ .B \-c .I count +] +.br +.ti +8 +[ +.B \-C +.I file_size ] [ .B \-F .I file @@ -77,32 +83,103 @@ tcpdump \- dump traffic on a network .SH DESCRIPTION .LP \fITcpdump\fP prints out the headers of packets on a network interface -that match the boolean \fIexpression\fP. +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 \-b +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 -.B Under SunOS with nit or bpf: -To run +When .I tcpdump -you must have read access to +finishes capturing packets, it will report counts of: +.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 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, it will +report those counts when it receives a SIGINFO signal (generated, for +example, by typing your ``status'' character, typically control-T) 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* . -.B Under Solaris with dlpi: +.TP +.B Under Solaris with DLPI: You must have read/write access to the network pseudo device, e.g. .IR /dev/le . -.B Under HP-UX with dlpi: -You must be root or it must be installed setuid to root. +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. +.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 it must be installed setuid to root. +You must be root or +.I tcpdump +must be installed setuid to root. +.TP .B Under Linux: -You must be root or it must be installed setuid to root. +You must be root or +.I tcpdump +must be installed setuid to root. +.TP .B Under Ultrix and Digital UNIX: Once the super-user has enabled promiscuous-mode operation using .IR pfconfig (8), -any user may run -.BR tcpdump . +any user may capture network traffic with +.IR tcpdump . +.TP .B Under BSD: You must have read access to .IR /dev/bpf* . +.LP +Reading a saved packet file doesn't require special privileges. .SH OPTIONS .TP .B \-a @@ -111,6 +188,16 @@ Attempt to convert network and broadcast addresses to names. .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 2 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. @@ -127,12 +214,13 @@ Dump packet-matching code as decimal numbers (preceded with a count). Print the link-level header on each dump line. .TP .B \-E -Use \fIalgo:secret\fP for decrypting IPsec ESP packets. Algorithms may be -\fBdes-cbc\fP, -\fB3des-cbc\fP, -\fBblowfish-cbc\fP, -\fBrc3-cbc\fP, -\fBcast128-cbc\fP, or +Use \fIalgo:secret\fP for decrypting IPsec ESP packets. +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 @@ -165,65 +253,86 @@ 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. +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. .TP .B \-l -Make stdout line buffered. Useful if you want to see the data -while capturing it. E.g., +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 \-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 \-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., +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 \-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 \-O -Do not run the packet-matching code optimizer. This is useful only +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 +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 +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 -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 +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 +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 +specified \fItype\fR. +Currently known types are \fBcnfp\fR (Cisco NetFlow protocol), \fBrpc\fR (Remote Procedure Call), \fBrtp\fR (Real-Time Applications protocol), @@ -233,15 +342,6 @@ specified \fItype\fR. Currently known types are and \fBwb\fR (distributed White Board). .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 \-S -Print absolute, rather than relative, TCP sequence numbers. -.TP .B \-t \fIDon't\fP print a timestamp on each dump line. .TP @@ -249,32 +349,39 @@ Print absolute, rather than relative, TCP sequence numbers. Print an unformatted timestamp on each dump line. .TP .B \-ttt -Print a delta (in micro-seconds) between current and previous line +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. +.B \-u +Print undecoded NFS handles. .TP .B \-v -(Slightly more) verbose output. For example, the time to live, +(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. .TP .B \-vv -Even more verbose output. For example, additional fields are -printed from NFS reply packets. +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, +Even more verbose output. +For example, telnet \fBSB\fP ... \fBSE\fP options -are printed in full. With +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. +them out. +They can later be printed with the \-r option. Standard output is used if \fIfile\fR is ``-''. .TP .B \-x @@ -284,7 +391,8 @@ The smaller of the entire packet or bytes will be printed. .TP .B \-X -When printing hex, print ascii too. Thus if +When printing hex, print ascii too. +Thus if .B \-x is also set, the packet is printed in hex/ascii. This is very handy for analysing new protocols. @@ -294,15 +402,18 @@ is not also set, some parts of some packets may be printed in hex/ascii. .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, +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 +(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. @@ -311,7 +422,8 @@ Possible types are .B net and .BR port . -E.g., `host foo', `net 128.3', `port 20'. If there is no type +E.g., `host foo', `net 128.3', `port 20'. +If there is no type qualifier, .B host is assumed. @@ -325,7 +437,8 @@ Possible directions are and .B "src and" .BR dst . -E.g., `src foo', `dst net 128.3', `src or dst port ftp-data'. If +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. @@ -335,7 +448,8 @@ and .B outbound qualifiers can be used to specify a desired direction. .IP \fIproto\fP -qualifiers restrict the match to a particular protocol. Possible +qualifiers restrict the match to a particular protocol. +Possible protos are: .BR ether , .BR fddi , @@ -348,9 +462,11 @@ protos are: .B tcp and .BR udp . -E.g., `ether src foo', `arp net 128.3', `tcp port 21'. If there is +E.g., `ether src foo', `arp net 128.3', `tcp port 21'. +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' +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 @@ -359,7 +475,8 @@ 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, +analogous Ethernet fields. +FDDI headers also contain other fields, but you cannot name them explicitly in a filter expression. .LP Similarly, `tr' is an alias for `ether'; the previous paragraph's @@ -371,15 +488,18 @@ that don't follow the pattern: .BR broadcast , .BR less , .B greater -and arithmetic expressions. All of these are described below. +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., +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 @@ -407,7 +527,8 @@ which is equivalent to: 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 +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). @@ -416,11 +537,15 @@ 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 +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 in both /etc/hosts and /etc/ethers. (An equivalent -expression is +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 @@ -430,7 +555,8 @@ 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 +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 @@ -438,12 +564,13 @@ 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 \fImask\fR" -True if the IP address matches \fInet\fR with the specific netmask. +.IP "\fBnet \fInet\fR \fBmask \fInetmask\fR" +True if the IP 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 a netmask \fIlen\fR bits wide. +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 @@ -453,7 +580,8 @@ The \fIport\fP can be a number or a name used in /etc/services (see 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, +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). @@ -491,13 +619,13 @@ True if the packet is an IP packet (see of protocol type \fIprotocol\fP. \fIProtocol\fP can be a number or one of the names \fIicmp\fP, \fIicmp6\fP, \fIigmp\fP, \fIigrp\fP, \fIpim\fP, \fIah\fP, -\fIesp\fP, \fIudp\fP, or \fItcp\fP. +\fIesp\fP, \fIvrrp\fP, \fIudp\fP, or \fItcp\fP. Note that the identifiers \fItcp\fP, \fIudp\fP, and \fIicmp\fP are also keywords and must be escaped via backslash (\\), which is \\\\ in the C-shell. -Note that this primitive does not chase protocol header chain. +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 protocol header chain. +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 @@ -518,14 +646,17 @@ 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 +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 IP broadcast packet. It checks for both +True if the packet is an IP broadcast packet. +It checks for both the all-zeroes and all-ones broadcast conventions, and looks up the local subnet mask. .IP "\fBether multicast\fR" -True if the packet is an ethernet multicast packet. The \fIether\fP +True if the packet is an ethernet multicast packet. +The \fIether\fP keyword is optional. This is shorthand for `\fBether[0] & 1 != 0\fP'. .IP "\fBip multicast\fR" @@ -536,21 +667,46 @@ True if the packet is an IPv6 multicast packet. True if the packet is of ether type \fIprotocol\fR. \fIProtocol\fP can be a number or one of the names \fIip\fP, \fIip6\fP, \fIarp\fP, \fIrarp\fP, \fIatalk\fP, \fIaarp\fP, -\fIdecnet\fP, \fIsca\fP, \fIlat\fP, \fImopdl\fP, \fImoprc\fP, or -\fIiso\fP. +\fIdecnet\fP, \fIsca\fP, \fIlat\fP, \fImopdl\fP, \fImoprc\fP, +\fIiso\fP, \fIstp\fP, \fIipx\fP, or \fInetbeui\fP. Note these identifiers are also keywords and must be escaped via backslash (\\). -[In the case of FDDI (e.g., `\fBfddi protocol arp\fR'), the -protocol identification comes from the 802.2 Logical Link Control -(LLC) header, which is usually layered on top of the FDDI header. -\fITcpdump\fP assumes, when filtering on the protocol identifier, -that all FDDI packets include an LLC header, and that the LLC header -is in so-called SNAP format. The same applies to Token Ring.] +.IP +[In the case of FDDI (e.g., `\fBfddi protocol arp\fR') and Token Ring +(e.g., `\fBtr 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 or Token Ring +header. +.IP +When filtering for most protocol identifiers on FDDI or Token Ring, +\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. +.IP +The exceptions are \fIiso\fP, for which it checks the DSAP (Destination +Service Access Point) and SSAP (Source Service Access Point) fields of +the LLC header, \fIstp\fP and \fInetbeui\fP, where it checks the DSAP of +the LLC header, and \fIatalk\fP, where it checks for a SNAP-format +packet with an OUI of 0x080007 and the Appletalk etype. +.IP +In the case of Ethernet, \fItcpdump\fR checks the Ethernet type field +for most of those protocols; the exceptions are \fIiso\fP, \fIsap\fP, +and \fInetbeui\fP, for which it checks for an 802.3 frame and then +checks the LLC header as it does for FDDI and Token Ring, \fIatalk\fP, +where it checks both for the Appletalk etype in an Ethernet frame and +for a SNAP-format packet as it does for FDDI and Token Ring, \fIaarp\fP, +where it checks for the Appletalk ARP etype in either an Ethernet frame +or an 802.2 SNAP frame with an OUI of 0x000000, and \fIipx\fP, where it +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.] .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 +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 @@ -558,7 +714,7 @@ True if the DECNET destination address is .IP "\fBdecnet host \fIhost\fR" True if either the DECNET source or destination address is .IR host . -.IP "\fBip\fR, \fBip6\fR, \fBarp\fR, \fBrarp\fR, \fBatalk\fR, \fBaarp\fR, \fBdecnet\fR, \fBiso\fR" +.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 @@ -630,7 +786,8 @@ length of the packet. For example, `\fBether[0] & 1 != 0\fP' catches all multicast traffic. The expression `\fBip[0] & 0xf != 5\fP' -catches all IP packets with options. The expression +catches all IP packets with options. +The expression `\fBip[6:2] & 0x1fff = 0\fP' catches only unfragmented datagrams and frag zero of fragmented datagrams. This check is implicitly applied to the \fBtcp\fP and \fBudp\fP @@ -638,6 +795,23 @@ 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-push\fP, +\fBtcp-ack\fP, \fBtcp-urg\fP. .LP Primitives may be combined using: .IP @@ -652,7 +826,8 @@ 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, +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 @@ -737,7 +912,7 @@ TCP conversation that involves a non-local host. .RS .nf .B -tcpdump 'tcp[13] & 3 != 0 and not src and dst net \fIlocalnet\fP' +tcpdump 'tcp[tcpflags] & (tcp-syn|tcp-fin) != 0 and not src and dst net \fIlocalnet\fP' .fi .RE .LP @@ -764,12 +939,13 @@ ping packets): .RS .nf .B -tcpdump 'icmp[0] != 8 and icmp[0] != 0' +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 +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 @@ -784,18 +960,23 @@ 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 +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 +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 +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 @@ -832,7 +1013,8 @@ data and 6 bytes of compressed header: .HD ARP/RARP Packets .LP -Arp/rarp output shows the type of request and its arguments. The +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: @@ -845,11 +1027,12 @@ arp reply csam is-at CSAM\fR .fi .RE The first line says that rtsg sent an arp packet asking -for the ethernet address of internet host csam. Csam +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 \fBtcpdump \-n\fP: +This would look less redundant if we had done \fItcpdump \-n\fP: .RS .nf .sp .5 @@ -858,7 +1041,7 @@ arp reply 128.3.254.6 is-at 02:07:01:00:01:c4\fP .fi .RE .LP -If we had done \fBtcpdump \-e\fP, the fact that the first packet is +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 @@ -875,7 +1058,8 @@ contained hex 0806 (type ETHER_ARP) and the total length was 64 bytes. TCP Packets .LP \fI(N.B.:The following description assumes familiarity with -the TCP protocol described in RFC-793. If you are not familiar +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 @@ -888,7 +1072,8 @@ The general format of a tcp protocol line is: .fi .RE \fISrc\fP and \fIdst\fP are the source and destination IP -addresses and ports. \fIFlags\fP are some combination of S (SYN), +addresses and ports. +\fIFlags\fP are some combination of S (SYN), F (FIN), P (PUSH) or R (RST) or a single `.' (no flags). \fIData-seqno\fP describes the portion of sequence space covered by the data in this packet (see example below). @@ -899,7 +1084,8 @@ 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 +\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 @@ -922,7 +1108,8 @@ csam.login > rtsg.1023: P 3:4(1) ack 21 win 4077 urg 1\fR\s+2 .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. +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 @@ -932,25 +1119,31 @@ 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 +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 +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 +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 +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 +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, @@ -959,22 +1152,25 @@ csam sends two bytes of urgent, pushed data to rtsg. 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 +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 +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 6 bits in the control bits section of the TCP header: +There are 8 bits in the control bits section of the TCP header: .IP -.I URG | ACK | PSH | RST | SYN | FIN +.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 +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 @@ -989,8 +1185,10 @@ regard to the TCP control bits is .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 +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: @@ -1004,14 +1202,15 @@ Recall the structure of a TCP header without options: ----------------------------------------------------------------- | acknowledgment number | ----------------------------------------------------------------- -| HL | reserved |U|A|P|R|S|F| window size | +| 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 fist line of the graph contains octets 0 - 3, the +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 @@ -1020,7 +1219,7 @@ in octet 13: .nf 0 7| 15| 23| 31 ----------------|---------------|---------------|---------------- -| HL | reserved |U|A|P|R|S|F| window size | +| HL | rsvd |C|E|U|A|P|R|S|F| window size | ----------------|---------------|---------------|---------------- | | 13th octet | | | .fi @@ -1030,15 +1229,14 @@ Let's have a closer look at octet no. 13: .nf | | |---------------| - | |U|A|P|R|S|F| + |C|E|U|A|P|R|S|F| |---------------| |7 5 3 0| .fi .PP -We see that this octet contains 2 bytes from the reserved field. -According to RFC 793 this field is reserved for future use and must -be 0. The remaining 6 bits are the TCP control bits we are interested -in. We have numbered the bits in this octet from 0 to 7, right to +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. @@ -1046,15 +1244,14 @@ Let's see what happens to octet 13 if a TCP datagram arrives with the SYN bit set in its header: .PP .nf - | |U|A|P|R|S|F| + |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 -We already mentioned that bits number 7 and 6 belong to the -reserved field, so they must must be 0. Looking at the +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 @@ -1091,18 +1288,20 @@ 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 +same time. +Let's see what happens to octet 13 when a TCP datagram with SYN-ACK set arrives: .PP .nf - | |U|A|P|R|S|F| + |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 +Now bits 1 and 4 are set in the 13th octet. +The binary value of octet 13 is .IP 00010010 @@ -1116,12 +1315,14 @@ which translates to decimal .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 +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, +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 @@ -1165,7 +1366,8 @@ UDP format is illustrated by this rwho packet: .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. +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. @@ -1175,7 +1377,8 @@ RPC calls (RFC-1050) to NFS. 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 +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 @@ -1191,18 +1394,23 @@ Name server requests are formatted as .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 +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 +\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, name server or -authority section, +square brackets: If a query contains an answer, authority records or +additional records section, .IR ancount , .IR nscount , or @@ -1227,48 +1435,59 @@ helios.domain > h2opolo.1537: 2 NXDomain* 0/1/0 (97)\fR .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 authority records. +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 +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 +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 +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' +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. +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 +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. If you are decoding SMB sessions containing unicode strings then you -may wish to set the environment variable USE_UNICODE to 1. A patch to +may wish to set the environment variable USE_UNICODE to 1. +A patch to auto-detect unicode srings would be welcome. For information on SMB packet formats and what all te fields mean see www.cifs.org or the pub/samba/specs/ directory on your favourite -samba.org mirror site. The SMB patches were written by Andrew Tridgell +samba.org mirror site. +The SMB patches were written by Andrew Tridgell (tridge@samba.org). .HD @@ -1294,8 +1513,10 @@ wrl.nfs > sushi.201b: .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 +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 @@ -1303,8 +1524,10 @@ 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 +`\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 @@ -1325,11 +1548,13 @@ wrl.nfs > sushi.1372a: (\-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 +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 +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. @@ -1337,12 +1562,15 @@ the file mode (in octal), the uid and gid, and the file size. 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 +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, +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 +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 @@ -1366,15 +1594,19 @@ pike.afsfs > elvis.7001: rx data fs reply rename .sp .5 .fi .RE -In the first line, host elvis sends a RX packet to pike. This was +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 +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 +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 +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 @@ -1398,12 +1630,15 @@ 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' +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, +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 +replies using the call number and service ID. +If a reply does not closely follow the corresponding request, it might not be parsable. @@ -1412,7 +1647,8 @@ 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 +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 @@ -1427,7 +1663,8 @@ Lines in this file have the form .sp .5 .fi .RE -The first two lines give the names of appletalk networks. The third +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 @@ -1457,14 +1694,16 @@ 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 +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 +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. @@ -1479,10 +1718,12 @@ techpit.2 > icsd-net.112.220: nbp-reply 190: "techpit:LaserWriter@*" 186\fR\s+2 .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. +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 +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. @@ -1508,18 +1749,24 @@ jssmag.209.133 > helios.132: atp-req* 12267<0-7> 0xae030002\fR\s+2 .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 +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 +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 +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 +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 @@ -1534,16 +1781,21 @@ Fragmented Internet datagrams are printed as .sp .5 .fi .RE -(The first form indicates there are more fragments. The second +(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 +\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 +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 +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 @@ -1558,12 +1810,14 @@ rtsg.1170 > arizona.ftp-data: . ack 1536 win 2560\fP\s+2 .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 +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 +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 @@ -1572,7 +1826,8 @@ trailing \fB(DF)\fP. .HD Timestamps .LP -By default, all output lines are preceded by a timestamp. The timestamp +By default, all output lines are preceded by a timestamp. +The timestamp is the current clock time in the form .RS .nf @@ -1580,7 +1835,8 @@ is the current clock time in the form .fi .RE and is as accurate as the kernel's clock. -The timestamp reflects the time the kernel first saw the packet. No attempt +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. @@ -1647,7 +1903,8 @@ 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 +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 @@ -1655,8 +1912,10 @@ skewed time stamps (the time change is ignored). .LP Filter expressions that manipulate FDDI or Token Ring headers assume that all FDDI and Token Ring packets are SNAP-encapsulated Ethernet -packets. This is true for IP, ARP, and DECNET Phase IV, but is not true -for protocols such as ISO CLNS. Therefore, the filter may inadvertently +packets. +This is true for IP, ARP, and DECNET Phase IV, but is not true +for protocols such as ISO CLNS. +Therefore, the filter may inadvertently accept certain packets that do not properly match the filter expression. .LP Filter expressions on fields other than those that manipulate Token Ring |
