pcap-filter - packet filter syntax

pcap_compile() is used to compile a string into a filter program, which can then be applied to a stream of packets to determine which ones will be supplied to pcap_loop, pcap_dispatch, pcap_next, or pcap_next_ex and tcpdump?

The filter expression consists of one or more which usually consist of an id (name or number) preceded by one or more qualifiers.

Qualifiers:

type what kind of thing the id name or number refers to.
host, net, port and portrange.
Example: host foo, net 128.3, port 20, portrange 6000-6008. Default host.

direction to and/or from id.
src, dst, src or dst, src and dst, ra, ta, addr1, addr2, addr3, and addr4.
Default: src or dst
Example: src foo, dst net 128.3, src or dst port ftp-data.
ra, ta, addr1, addr2, addr3, and addr4 qualifiers are only valid for IEEE 802.11 Wireless LAN link layers.
For some link layers, such as SLIP and the cooked Linux capture mode used for the any device and for some other device types,
inbound and outbound qualifiers can be used .

proto

protos are: ether, fddi, tr, wlan, ip, ip6, arp, rarp, decnet, tcp and udp.
Examples: ether src foo, arp net 128.3, tcp port 21, udp portrange 7000-7009,
wlan addr2 0:2:3:4:5:6.
If there is no proto qualifier, all protocols consistent with the type are assumed.
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 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.

tr and wlan are aliases for ether; the previous paragraphs 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.]

Special primitive keywords : gateway, broadcast, less, greater and arithmetic expressions.

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 the same as
tcp dst port ftp or tcp dst port ftp-data or tcp dst port domain.

primitives :

dst host host True if the IPv4/v6 destination field of the packet is host,either an address or a name.

src host host True if the IPv4/v6 source field of the packet is host.

host host

True if either the IPv4/v6 source or destination of the packet is host.

Any of the above host expressions can be prepended with the keywords, ip, arp, rarp, or ip6 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, 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, 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

ether host ehost and not host host

which can be used with either names or numbers for host / ehost.) This syntax does not work in IPv6-enabled configuration

dst net net True if the IPv4/v6 destination address of the packet has a network number of net, may be either a name from the networks database (/etc/networks, etc.) or a network number.
An IPv4 network number can be written as a dotted quad (e.g., 192.168.1.0), dotted triple (e.g., 192.168.1), dotted pair (e.g, 172.16), or single number (e.g., 10); the netmask is 255.255.255.255 for a dotted quad (which means that it's really a host match), 255.255.255.0 for a dotted triple, 255.255.0.0 for a dotted pair, or 255.0.0.0 for a single number. An IPv6 network number must be written out fully; the netmask is ff:ff:ff:ff:ff:ff:ff:ff, so IPv6 "network" matches are really always host matches, and a network match requires a netmask length.

src net net True if the IPv4/v6 source address of the packet has a network number of net.

net net True if either the IPv4/v6 source or destination address of the packet has a network number of net.

net net mask netmask True if the IPv4 address matches net with the specific netmask. May be qualified with src or dst. Note that this syntax is not valid for IPv6 net.

net net/len True if the IPv4/v6 address matches net with a netmask len bits wide. May be qualified with src or dst.

dst port port True if the packet is ip/tcp, ip/udp, ip6/tcp or ip6/udp and has a destination port value of portcan 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 traffic, 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.

dst portrange port1-port2 True if the packet is ip/tcp, ip/udp, ip6/tcp or ip6/udp and has a destination port value between port1 and port2. port1 and port2 are interpreted in the same fashion as the port parameter for port.

src portrange port1-port2 True if the packet has a source port value between port1 and port2.

portrange port1-port2 True if either the source or destination port of the packet is between port1 and port2. Any of the above port or port range 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 IPv4 packet (see ip(4P)) of protocol type protocol. Protocol can be a number or one of the names icmp, icmp6, igmp, igrp, pim, ah, esp, vrrp, udp, 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. Note that this primi- tive does not chase the protocol header chain.

ip6 proto protocol True if the packet is an IPv6 packet of protocol type protocol. Note that this primitive does not chase the protocol header chain.

ip6 protochain protocol True if the packet is IPv6 packet, and contains protocol header with type protocol in its protocol header chain. For example, ip6 protochain 6 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 the BPF optimizer code, so this can be somewhat slow.

ip protochain protocol Equivalent to ip6 protochain protocol, but this is for IPv4.

ether broadcast True if the packet is an Ethernet broadcast packet. The ether keyword is optional.

ip broadcast

True if the packet is an IPv4 broadcast packet. It checks for both the all-zeroes and all-ones broadcast con- ventions, and looks up the subnet mask on the interface on which the capture is being done.

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.

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 IPv4 multicast packet.

ip6 multicast True if the packet is an IPv6 multicast packet.

ether proto protocol

True if the packet is of ether type protocol. Protocol can be a number or one of the names

ip, ip6, arp, rarp,
              atalk, aarp, decnet, sca, lat, mopdl, moprc, iso, stp, ipx, or netbeui

. Note these identifiers are also keywords and must be escaped via backslash (\).

[In the case of FDDI (e.g., fddi protocol arp), Token Ring (e.g., tr protocol arp), and IEEE 802.11 wireless LANS (e.g., wlan protocol arp), 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.

When filtering for most protocol identifiers on FDDI, Token Ring, or 802.11, 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:

`iso`	checks the DSAP (Destination Service Access Point) and SSAP (Source Service Access Point) fields of the LLC header;
`stp and netbeui`	checks the DSAP of the LLC header;
`atalk`	checks for a SNAP-format packet with an OUI of 0x080007 and the AppleTalk etype.

In the case of Ethernet, checks the Ethernet type field for most of those protocols. The exceptions are:

`iso, stp, and netbeui`	checks for an 802.3 frame and then checks the LLC header as it does for FDDI, Token Ring, and 802.11;
`atalk`	the filter 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;
`aarp`	checks for the AppleTalk ARP etype in either an Ethernet frame or an 802.2 SNAP frame with an OUI of 0x000000;
`ipx`	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.

DECNET

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.

ifname interface True if the packet was logged as coming from the specified interface (applies only to packets logged by OpenBSD's or FreeBSD's pf(4)).

on interface Synonymous with the ifname modifier.

rnr num True if the packet was logged as matching the specified PF rule number (applies only to packets logged by OpenBSD's or FreeBSD's pf(4)).

rulenum num Synonymous with the rnr modifier.

reason code True if the packet was logged with the specified PF reason code.
The known codes are: match, bad-offset, fragment, short, normalize, and memory (applies only to packets logged by OpenBSD's or FreeBSD's pf(4)).

rset name True if the packet was logged as matching the specified PF ruleset name of an anchored ruleset (applies only to packets logged by OpenBSD's or FreeBSD's pf(4)).

ruleset name Synonomous with the rset modifier.

srnr num True if the packet was logged as matching the specified PF rule number of an anchored ruleset (applies only to packets logged by OpenBSD's or FreeBSD's pf(4)).

subrulenum num Synonomous with the srnr modifier.

action act True if PF took the specified action when the packet was logged. Known actions are: pass and block and, with later versions of pf(4)), nat, rdr, binat and scrub (applies only to packets logged by OpenBSD's or FreeBSD's pf(4)).

802.11

wlan ra ehost True if the IEEE 802.11 RA is ehost. The RA field is used in all frames except for management frames.

wlan ta ehost True if the IEEE 802.11 TA is ehost. The TA field is used in all frames except for management frames and CTS (Clear To Send) and ACK (Acknowledgment) control frames.

wlan addr1 ehost True if the first IEEE 802.11 address is ehost.

wlan addr2 ehost True if the second IEEE 802.11 address, if present, is ehost. The second address field is used in all frames except for CTS (Clear To Send) and ACK (Acknowledgment) control frames.

wlan addr3 ehost True if the third IEEE 802.11 address, if present, is ehost. The third address field is used in management and data frames, but not in control frames.

wlan addr4 ehost True if the fourth IEEE 802.11 address, if present, is ehost. The fourth address field is only used for WDS (Wireless Distribution System) frames.

ip, ip6, arp, rarp, atalk, aarp, decnet, iso, stp, ipx, netbeui 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 not all applications using pcap(3) currently know how to parse these protocols.

type wlan_type True if the IEEE 802.11 frame type matches : mgt, ctl and data.

type wlan_type subtype wlan_subtype

True if the IEEE 802.11 frame type matches and frame subtype matches the specified wlan_subtype.
If the specified wlan_type is mgt, then valid wlan_subtypes are: assoc-req, assoc-resp, reassoc-req, reassocresp, probe-req, probe-resp, beacon, atim, disassoc, auth and deauth.

If the specified wlan_type is ctl, then valid wlan_subtypes are: ps-poll, rts, cts, ack, cf-end and cf-end-ack.
If the specified wlan_type is data, then valid wlan_subtypes are: data, data-cf-ack, data-cf-poll, data-cf-ackpoll, null, cf-ack, cf-poll, cf-ack-poll, qos-data, qos-data-cf-ack, qos-data-cf-poll, qos-data-cf-ack-poll, qos, qos-cf-poll and qos-cf-ack-poll.

subtype wlan_subtype True if the IEEE 802.11 frame subtype matches the specified wlan_subtype and frame has the type to which the specified wlan_subtype belongs.

dir dir True if the IEEE 802.11 frame direction matches dir. Valid directions are:
nods, tods, fromds, dstods or a numeric value.

vlan [vlan_id] True if the packet is an IEEE 802.1Q VLAN packet. If [vlan_id] is specified, only true if the packet has the specified vlan_id. Note that the first vlan keyword encountered in expression changes the decoding offsets for the remainder of expression on the assumption that the packet is a VLAN packet. The vlan [vlan_id] expression may be used more than once, to filter on VLAN hierarchies. Each use of that expression increments offsets by 4. For example: vlan 100 && vlan 200 filters on VLAN 200 encapsulated within VLAN 100, and vlan && vlan 300 && ip filters IPv4 protocols encapsulated in VLAN 300 encapsulated within any higher order VLAN.

mpls [label_num] True if the packet is an MPLS packet. If [label_num] is specified, only true is the packet has the specified label_num. Note that the first mpls keyword encountered in expression changes the decoding offsets for the remainder of expression on the assumption that the packet is a MPLS-encapsulated IP packet. The mpls [label_num] expression may be used more than once, to filter on MPLS hierarchies. Each use of that expression increments offsets by 4. For example: mpls 100000 && mpls 1024 filters packets with an outer label of 100000 and an inner label of 1024, and mpls && mpls 1024 && host 192.9.200.1 filters packets to or from 192.9.200.1 with an inner label of 1024 and any outer label.

pppoed True if the packet is a PPP-over-Ethernet Discovery packet (Ethernet type 0x8863).

pppoes True if the packet is a PPP-over-Ethernet Session packet (Ethernet type 0x8864). Note that the first pppoes keyword encountered in expression changes the decoding offsets for the remainder of expression on the assumption that the packet is a PPPoE session packet. For example: pppoes && ip filters IPv4 protocols encapsulated in PPPoE.

tcp, udp, icmp Abbreviations for: ip proto p or ip6 proto p where p is one of the above protocols.

iso proto protocol True if the packet is an OSI packet of protocol type protocol. Protocol can be a number or one of the names clnp, esis, or isis.

clnp, esis, isis Abbreviations for: iso proto p

l1, l2, iih, lsp, snp, csnp, psnp Abbreviations for IS-IS PDU types.

ATM packet, for sunATM on Solaris

vpi n True , with a virtual path identifier of n.

vci n True , with a virtual channel identifier of n.

lane True , and is an ATM LANE packet. Note that the first lane keyword encountered in expression changes the tests done in the remainder of expression on the assumption that the packet is either a LANE emulated Ethernet packet or a LANE LE Control packet. If lane isn't specified, the tests are done under the assumption that the packet is an LLC-encapsulated packet.

llc True , and is an LLC-encapsulated packet.

oamf4s True , and is a segment OAM F4 flow cell (VPI=0 & VCI=3).

oamf4e True , and is an end-to-end OAM F4 flow cell (VPI=0 & VCI=4).

oamf4 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)).

oam True , and is a segment or end-to-end OAM F4 flow cell (VPI=0 & (VCI=3 | VCI=4)).

metac True , and is on a meta signaling circuit (VPI=0 & VCI=1).

bcc True , and is on a broadcast signaling circuit (VPI=0 & VCI=2).

sc True , and is on a signaling circuit (VPI=0 & VCI=5).

ilmic True , and is on an ILMI circuit (VPI=0 & VCI=16).

connectmsg True , and is on a signaling circuit and is a Q.2931 Setup, Call Proceeding, Connect, Connect Ack, Release, or Release Done message.

metaconnect True , and is on a meta signaling circuit and is a Q.2931 Setup, Call Proceeding, Connect, Release, or Release Done message.

expr relop expri

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.
all comparisons are unsigned, so that, for example, 0x80000000 and 0xffffffff are > 0.

To access data inside the packet, use the following syntax: proto [ expr : size ] Proto is one of ether, fddi, tr, wlan, ppp, slip, link, ip, arp, rarp, tcp, udp, icmp, ip6 or radio, and indicates the protocol layer for the index operation. (ether, fddi, wlan, tr, ppp, slip and link all refer to the link layer. radio refers to the "radio header" added to some 802.11 captures.) Note that tcp, udp 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 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, indi- cated 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 IPv4 packets with options.
The expression `ip[6:2] & 0x1fff = 0' catches only unfragmented IPv4 datagrams and frag zero of fragmented IPv4 datagrams. This check is implicitly applied to the tcp and udp index operations. For instance, tcp[0] always means the first byte of the TCP header, 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: icmptype type, icmpcode code and tcpflags flags

ICMP values : icmp-echoreply, icmp-unreach, icmp-sourcequench, icmp-redirect, icmp-echo, icmp-routeradvert, icmp-routersolicit, icmp-timxceed, icmp-paramprob, icmp-tstamp, icmp-tstampreply, icmp-ireq, icmp-ireqreply, icmp-maskreq, icmp-maskreply.
TCP flags : tcp-fin, tcp-syn, tcp-rst, tcp-push, tcp-ack, tcp-urg.

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 )

EXAMPLES

To select all packets arriving at or departing from sundown:

host sundown

To select traffic between helios and either hot or ace:

host helios and \( hot or ace \)

To select all IP packets between ace and any host except helios:

ip host ace and not helios

To select all traffic between local hosts and hosts at Berkeley:

net ucb-ether

To select all ftp traffic through internet gateway snup:

gateway snup and (port ftp or ftp-data)

To select 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).

ip and not net localnet

To select the start and end packets (the SYN and FIN packets) of each TCP conversation that involves a non-local host.

tcp[tcpflags] & (tcp-syn|tcp-fin) != 0 and not src and dst net localnet

To select 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.)

tcp port 80 and (((ip[2:2] - ((ip[0]&0xf)<<2)) - ((tcp[12]&0xf0)>>2)) != 0)

To select IP packets longer than 576 bytes sent through gateway snup:

gateway snup and ip[2:2] > 576

To select IP broadcast or multicast packets that were not sent via Ethernet broadcast or multicast:

ether[0] & 1 = 0 and ip[16] >= 224

To select all ICMP packets that are not echo requests/replies (i.e., not ping packets):

icmp[icmptype] != icmp-echo and icmp[icmptype] != icmp-echoreply

AUTHORS

       The original authors are:

       Van Jacobson, Craig Leres and Steven McCanne, all of the Lawrence Berkeley National Laboratory, University of  Califor-
       nia, Berkeley, CA.

       It is currently being maintained by tcpdump.org.

       The current version of libpcap is available via http:

              http://www.tcpdump.org/

       The original distribution is available via anonymous ftp:

              ftp://ftp.ee.lbl.gov/tcpdump.tar.Z

BUGS
       Please send problems, bugs, questions, desirable enhancements, etc. to:

              tcpdump-workers@lists.tcpdump.org

       Filter  expressions on fields other than those in Token Ring headers will not correctly handle source-routed Token Ring
       packets.

       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.

       ip6 proto should chase header chain, but at this moment it does not.  ip6 protochain is supplied for this behavior.

       Arithmetic  expression against transport layer headers, like tcp[0], does not work against IPv6 packets.  It only looks
       at IPv4 packets.

pcap-filter - packet filter syntax

primitives :

Primitives may be combined using:

EXAMPLES

SEE ALSO

AUTHORS