tcpflow(1) tcpflow 1.2.6 tcpflow(1) NAME tcpflow - TCP flow recorder SYNOPSIS tcpflow [-BcCehPpsv] [-b max_bytes] [-d debug_level] [-f max_fds] [-i iface] [-r file] [-m minskip] [-X file.xml] [-F[outputformat]] [-T[filenameetemplate]] [expression] DESCRIPTION tcpflow is a program that captures data transmitted as part of TCP con‐ nections (flows), and stores the data in a way that is convenient for protocol analysis or debugging. A program like tcpdump(4) shows a sum‐ mary of packets seen on the wire, but usually doesn't store the data that's actually being transmitted. In contrast, tcpflow reconstructs the actual data streams and stores each flow in a separate file for later analysis. tcpflow understands TCP sequence numbers and will cor‐ rectly reconstruct data streams regardless of retransmissions or out- of-order delivery. tcpflow stores all captured data in files that have names of the form 192.168.101.102.02345-010.011.012.013.45103 where the contents of the above file would be data transmitted from host 192.168.101.102 port 2345, to host 10.11.12.13 port 45103. OPTIONS -B Force binary output even when printing to console with -C or -c. -b Max bytes per flow. Capture no more than max_bytes bytes per flow. Any data captured for a flow beyond max_bytes from the first byte captured will be discarded. The default is to store an unlimited number of bytes per flow. -c Console print. Print the contents of packets to stdout as they are received, without storing any captured data to files (implies -C Console print without the packet source and destination details being printed. Print the contents of packets to stdout as they are received, without storing any captured data to files (implies -e When outputting to the console each flow will be output in different colors (blue for client to server flows, red for server to client flows, green for undecided flows). -s ). -d Debug level. Set the level of debugging messages printed to stderr to debug_level. Higher numbers produce more messages. -d 0 causes completely silent operation. -d 1 , the default, produces minimal status messages. -d 10 produces verbose output equivalent to -v . Numbers higher than 10 can produce a large amount of debugging information useful only to developers. -F[format] Specifies format for output filenames. Format specifiers: t prepends each filename with a Unix timestamp. T prepends each filename with an ISO-8601 timestamp. c appends each filename with a connection counter. -FM Include MD5 of each flow in the DFXML output. -FX Suppresses file output entirely (DFXML file is still produced). -T[format] Specifies an arbitrary template for filenames. %A expands to source IP address. %a expands to source IP port. %B expands to destination IP address. %a expands to destination IP port. %T expands to timestamp in ISO8601 format. %t expands to timestamp in Unix time_t format. %V expands to "--" if a VLAN is present. %v expands to the VLAN number if a VLAN is present. %C expands to "c" if the connection count>0. %c expands to the connection count if the connection count>0. %# always expands to the con‐ nection count. %% prints a "%". -AH Perform HTTP post-processing ("After" processing). If the output file is 208.111.153.175.00080-192.168.001.064.37314, Then the post-processing will create the files: 208.111.153.175.00080-192.168.001.064.37314-HTTP 208.111.153.175.00080-192.168.001.064.37314-HTTPBODY If the HTTPBODY was compressed with GZIP, you may get a third file as well: 208.111.153.175.00080-192.168.001.064.37314-HTTPBODY-GZIP Additional information about these streams, such as their MD5 hash value, is also written to the DFXML file -fmax_fds Max file descriptors used. Limit the number of file descriptors used by tcpflow to max_fds. Higher numbers use more system resources, but usually perform better. If the underlying oper‐ ating system supports the setrlimit() system call, the OS will be asked to enforce the requested limit. The default is for tcpflow to use the maximum number of file descriptors allowed by the OS. The -v option will report how many file descriptors tcpflow is using. -h Help. Print usage information and exit. -i Interface name. Capture packets from the network interface named iface. If no interface is specified with -i , a reason‐ able default will be used by libpcap automatically. -m min_size Forces a new connection output file when there is a skip in the TCP session of min_size bytes or more. -P No purge. Normally tcpflow removes connections from the hash ta‐ ble after the connection is closed with a FIN. This conserves memory but takes additional CPU time. Selecting this option causes the std::tr1:unordered_map to grow without bounds, as tcpflow did prior to version 1.1. That makes tcpflow run faster if there are less than 10 million connections, but can lead to out-of-memory errors. -p No promiscuous mode. Normally, tcpflow attempts to put the net‐ work interface into promiscuous mode before capturing packets. The -p option tells tcpflow not to put the interface into pro‐ miscuous mode. Note that it might already be in promiscuous mode for some other reason. -r Read from file. Read packets from file, which was created using the -w option of tcpdump(1). Standard input is used if file is ``-''. Note that for this option to be useful, tcpdump's -s option should be used to set the snaplen to the MTU of the interface (e.g., 1500) while capturing packets. -s Strip non-printables. Convert all non-printable characters to the "." character before printing packets to the console or storing them to a file. -v Verbose operation. Verbosely describe tcpflow's operation. Equivalent to -d 10 . FILTERING EXPRESSIONS The expression specified on the command-line specifies which packets should be captured. Because tcpflow uses the the libpcap library, tcpflow has the same powerful filtering language available as programs such as tcpdump(1). The following part of the man page is excerpted from the tcpdump man page. expression selects which packets will be dumped. If no expression is given, all packets on the net will be dumped. Otherwise, only packets for which expression is `true' will be dumped. The expression consists of one or more primitives. Primitives usually consist of an id (name or number) preceded by one or more qualifiers. There are three different kinds of qualifier: type qualifiers say what kind of thing the id name or number refers to. Possible types are host, net and port. E.g., `host foo', `net 128.3', `port 20'. If there is no type qualifier, host is assumed. dir qualifiers specify a particular transfer direction to and/or from id. Possible directions are src, dst, src or dst and src and dst. E.g., `src foo', `dst net 128.3', `src or dst port ftp-data'. If there is no dir qualifier, src or dst is assumed. For `null' link layers (i.e. point to point protocols such as slip) the inbound and outbound qualifiers can be used to specify a desired direction. proto qualifiers restrict the match to a particular protocol. Possi‐ ble protos are: ether, fddi, ip, arp, rarp, decnet, lat, sca, moprc, mopdl, tcp and udp. E.g., `ether src foo', `arp net 128.3', `tcp port 21'. If there is no proto qualifier, all pro‐ tocols 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'. [`fddi' is actually an alias for `ether'; the parser treats them iden‐ tically 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.] In addition to the above, there are some special `primitive' keywords that don't follow the pattern: gateway, broadcast, less, greater and arithmetic expressions. All of these are described below. More complex filter expressions are built up by using the words and, or and 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'. Allowable primitives are: dst host host True if the IP destination field of the packet is host, which may be either an address or a name. src host host True if the IP source field of the packet is host. host host True if either the IP source or destination of the packet is host. Any of the above host expressions can be prepended with the keywords, ip, arp, or rarp as in: ip host host which is equivalent to: ether proto \ip and host host If host is a name with multiple IP addresses, each address will be checked for a match. ether dst ehost True if the ethernet destination address is ehost. Ehost may be either a name from /etc/ethers or a number (see ethers(3N) for numeric format). ether src ehost True if the ethernet source address is ehost. ether host ehost True if either the ethernet source or destination address is ehost. gateway host True if the packet used host as a gateway. I.e., the ethernet source or destination address was host but neither the IP source nor the IP destination was host. Host must be a name and must be found in both /etc/hosts and /etc/ethers. (An equivalent expression is ether host ehost and not host host which can be used with either names or numbers for host / ehost.) dst net net True if the IP destination address of the packet has a network number of net. Net may be either a name from /etc/networks or a network number (see networks(5) for details). src net net True if the IP source address of the packet has a network number of net. net net True if either the IP source or destination address of the packet has a network number of net. net net mask mask True if the IP address matches net with the specific netmask. May be qualified with src or dst. net net/len True if the IP address matches net a netmask len bits wide. May be qualified with src or dst. dst port port True if the packet is ip/tcp or ip/udp and has a destination port value of port. The port can be a number or a name used in /etc/services (see tcp(4P) and 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., dst port 513 will print both tcp/login traffic and udp/who traf‐ fic, and port domain will print both tcp/domain and udp/domain traffic). src port port True if the packet has a source port value of port. port port True if either the source or destination port of the packet is port. Any of the above port expressions can be prepended with the keywords, tcp or udp, as in: tcp src port port which matches only tcp packets whose source port is port. less length True if the packet has a length less than or equal to length. This is equivalent to: len <= length. greater length True if the packet has a length greater than or equal to length. This is equivalent to: len >= length. ip proto protocol True if the packet is an ip packet (see ip(4P)) of protocol type protocol. Protocol can be a number or one of the names icmp, igrp, udp, nd, or tcp. Note that the identifiers tcp, udp, and icmp are also keywords and must be escaped via backslash (\), which is \\ in the C-shell. ether broadcast True if the packet is an ethernet broadcast packet. The ether keyword is optional. ip broadcast 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. ether multicast True if the packet is an ethernet multicast packet. The ether keyword is optional. This is shorthand for `ether[0] & 1 != 0'. ip multicast True if the packet is an IP multicast packet. ether proto protocol True if the packet is of ether type protocol. Protocol can be a number or a name like ip, arp, or rarp. Note these identifiers are also keywords and must be escaped via backslash (\). [In the case of FDDI (e.g., `fddi protocol arp'), the protocol iden‐ tification comes from the 802.2 Logical Link Control (LLC) header, which is usually layered on top of the FDDI header. Tcpdump 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.] decnet src host True if the DECNET source address is 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.] decnet dst host True if the DECNET destination address is host. decnet host host True if either the DECNET source or destination address is host. ip, arp, rarp, decnet Abbreviations for: ether proto p where p is one of the above protocols. lat, moprc, mopdl Abbreviations for: ether proto p where p is one of the above protocols. Note that tcpdump does not currently know how to parse these protocols. tcp, udp, icmp Abbreviations for: ip proto p where p is one of the above protocols. expr relop expr True if the relation holds, where relop is one of >, <, >=, <=, =, !=, and expr 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. To access data inside the packet, use the following syntax: proto [ expr : size ] Proto is one of ether, fddi, ip, arp, rarp, tcp, udp, or icmp, and indicates the protocol layer for the index operation. The byte offset, relative to the indicated protocol layer, is given by expr. Size 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 len, gives the length of the packet. For example, `ether[0] & 1 != 0' catches all multicast traffic. The expression `ip[0] & 0xf != 5' catches all IP packets with options. The expression `ip[6:2] & 0x1fff = 0' catches only unfragmented datagrams and frag zero of fragmented datagrams. This check is implicitly applied to the tcp and udp index opera‐ tions. For instance, tcp[0] always means the first byte of the TCP header, and never means the first byte of an intervening fragment. Primitives may be combined using: A parenthesized group of primitives and operators (parentheses are special to the Shell and must be escaped). Negation (`!' or `not'). Concatenation (`&&' or `and'). Alternation (`||' or `or'). Negation has highest precedence. Alternation and concatenation have equal precedence and associate left to right. Note that explicit and tokens, not juxtaposition, are now required for concatenation. If an identifier is given without a keyword, the most recent keyword is assumed. For example, not host vs and ace is short for not host vs and host ace which should not be confused with not ( host vs or ace ) Expression arguments can be passed to tcpdump as either a single argu‐ ment or as multiple arguments, whichever is more convenient. Gener‐ ally, if the expression contains Shell metacharacters, it is easier to pass it as a single, quoted argument. Multiple arguments are concate‐ nated with spaces before being parsed. EXAMPLES The following part of the man page is excerpted from the tcpdump man page. To record all packets arriving at or departing from sundown: tcpflow host sundown To record traffic between helios and either hot or ace: tcpflow host helios and \( hot or ace \) To record traffic between ace and any host except helios: tcpflow host ace and not helios To record all traffic between local hosts and hosts at Berkeley: tcpflow net ucb-ether To record all ftp traffic through internet gateway snup: (note that the expression is quoted to prevent the shell from (mis-)interpreting the parentheses): tcpflow 'gateway snup and (port ftp or ftp-data)' BUGS Please send bug reports to simsong@acm.org. tcpflow currently does not understand IP fragments. Flows containing IP fragments will not be recorded correctly. tcpflow never frees state associated with flows that it records, so will grow large if used to capture a very large number of flows (e.g., on the order of 100,000 flows or more). There appears to be a bug in the way that Linux delivers packets to libpcap when using the loopback interface ("localhost"). When listen‐ ing to the Linux loopback interface, selective packet filtering is not possible; all TCP flows on the localhost interface will be recorded. AUTHORS Originally by Jeremy Elson . Substantially modi‐ fied and maintained by Simson L. Garfinkel . The current version of this software is available at http://www.afflib.org/ An announcement mailing list for this program is at: http://groups.google.com/group/tcpflow-users SEE ALSO tcpdump(1), nit(4P), bpf(4), pcap(3) tcpflow 1.2.6 15 Jan 2011 tcpflow(1)