pcap-filter(7) man page

Updated: 16 September 2026 • View in plain text • Index • Return to Main Contents

NAME

pcap-filter - packet filter syntax

DESCRIPTION

pcap_compile(3PCAP) is used to compile a string into a filter program. The resulting filter program can then be applied to some stream of packets to determine which packets will be supplied to pcap_loop(3PCAP), pcap_dispatch(3PCAP), pcap_next(3PCAP), or pcap_next_ex(3PCAP).

The filter expression consists of one or more primitives. Primitives usually consist of an id (a name, a number or something slightly more complex, such as a CIDR prefix) preceded by one or more qualifiers. There are three different kinds of qualifier:

proto: proto qualifiers restrict the match to a particular protocol. (This should not be confused with the proto type qualifier below.) Possible protocols are: ether, link, wlan, ip, ip6, arp, tcp, udp, sctp, iso, isis, rarp, decnet, fddi, tr, ppp and slip. E.g., **ether src** foo',arp net 128.3', **tcp port** 21',ip proto ospf', **ether proto** 0x88CC',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. E.g.,src foo' means **(ip6 or ip or arp or rarp) src** foo',proto tcp' means **(ip6 or ip) proto** tcp'net bar' means **(ip6 or ip or arp or rarp) net** bar' andport 53' means **(tcp or udp or sctp) port** 53' (note that these examples use invalid syntax to illustrate the principle). *dir*: *dir* qualifiers specify a particular transfer direction to and/or from *id*. Possible directions are **src**, **dst**, **src or dst**, **src and dst**, **ra**, **ta**, **addr1**, **addr2**, **addr3**, and **addr4**. 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. The **ra**, **ta**, **addr1**, **addr2**, **addr3**, and **addr4** qualifiers are only valid for IEEE 802.11 Wireless LAN link layers. *type*: *type* qualifiers say what kind of thing the id name or number refers to. Possible types are **host**, **net**, **proto**, **port**, **portrange**, **protochain** and **gateway.** E.g.,host foo', **net** 128.3',port 20', **portrange** 6000-6008',proto 17'. If there is no type qualifier, host is assumed.

In primitives that follow this pattern each qualifier kind may be present at most once, and if more than one kind is present, any proto qualifier must be the first qualifier and any type qualifier must be the last qualifier, for example, `tcp dst port 80'. Also not all combinations of these qualifier kinds are valid syntax. Some make no sense in network protocols space, for example: ether port (Ethernet header has no ports), tcp net (TCP header does not have layer 3 fields), dst proto (in a protocol header the same protocol applies to both the source and the destination), and so on. Some other combinations are not valid syntax because they are not implemented, even though hypothetically could make sense, for example: iso net, aarp host and so on.

[fddi is actually an alias for ether; the parser treats them identically as meaning ``the data link level used on the specified network interface''. FDDI headers contain Ethernet-like source and destination addresses, and often contain Ethernet-like packet types, so you can filter on these FDDI fields just as with the analogous Ethernet fields. FDDI headers also contain other fields, but you cannot name them explicitly in a filter expression. Similarly, tr and wlan are aliases for ether; the statements about FDDI headers also apply to Token Ring and 802.11 wireless LAN headers. The same stands for the link, ppp and slip keywords.]

For IEEE 802.11 headers, the destination address is the DA field and the source address is the SA field. For both ARP and RARP headers, the destination address is the TPA (Target Protocol Address) field and the source address is the SPA (Sender Protocol Address) field.

In addition to the above, there are some special `primitive' keywords that don't follow the pattern (for example: broadcast, multicast, inbound, outbound, ifindex, llc, vlan, mpls, less, greater), packet data accessors and relations of two arithmetic expressions. All of these are described below.

More complex filter expressions are built up by using the words and, or and not (or equivalently: **&&**',||' and **!**' respectively) 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 astcp dst port ftp or tcp dst port ftp-data or tcp dst port domain'.

PRIMITIVES

host hostnameaddr: True if the source or the destination ARP/IPv4/IPv6/RARP address of the packet is hostnameaddr. May be qualified with a specific protocol (arp, ip, ip6, rarp) and/or a different direction (src, dst, src and dst), in the latter case the host keyword is optional. For example, ip src hostnameaddr for Ethernet-like link-layer types is equivalent to ether proto \ip and ip src host hostnameaddr : hostnameaddr may be either an IPv4 host number or an IPv6 host number or a name. : An IPv4 host number can be written as a dotted quad (e.g., 192.168.10.20), dotted triple (e.g., 192.168.10 means the same as 192.168.10.0/24, so it is really a network match), dotted pair (e.g., 192.168 means 192.168.0.0/16, so it is really a network match as well), or single number (e.g., [decimal] 168496141, [octal] 01202606015 and [hexadecimal] 0x0a0b0c0d all mean 10.11.12.13). : An IPv6 host number can be written as a complete 128-bit address (x:x:x:x:x:x:x:x) or using the zero compression (x::x) or the IPv4-mapped (x:x:x:x:x:x:d.d.d.d) notations as discussed in inet_pton(3). In this primitive this version of libpcap tolerates an optional “/128” after an IPv6 host number, this behaviour is an implementation quirk and it may be removed in future. : A host name must resolve using getaddrinfo(3), which typically means DNS or hosts(5), to at least one IPv4 address for **arp host**',ip host' and **rarp host**', at least one IPv6 address forip6 host', and at least one IPv4/IPv6 address for **host**'. If the name resolves to more than one address, this primitive evaluates to true as soon as one of the addresses matches the packet. : When not qualified with a protocol, this primitive implies all protocols that make sense for the address families of the specified/resolved addresses. When qualified with a protocol, this primitive ignores the address family that does not make sense for the protocol. For example, for a name that resolves only to an IPv6 addressarp host' returns an error, but **host**' is valid and means IPv6, for a name that resolves only to an IPv4 addressip6 host' returns an error, but **host**' is valid and means ARP/IPv4/RARP, for a name that resolves to both IPv4 and IPv6 addressesip host' ignores the IPv6 addresses and **ip6 host**' ignores the IPv4 addresses, and so on. **ether host** *ethernameaddr*: True if the source or the destination Ethernet/802.11/IPFC/ATM LANE/FDDI/Token Ring address of the packet is *ethernameaddr*. May be qualified with a different direction (**src**, **dst**, **src and dst**), in which case the **host** keyword is optional. : *ethernameaddr* may be either a name from **ethers**(5) or a numerical MAC-48 address. In the latter case a valid format is one of “xx:xx:xx:xx:xx:xx”, “xx.xx.xx.xx.xx.xx” or “xx-xx-xx-xx-xx-xx”, where every “xx” is a hexadecimal digit (0-9, a-f, or A-F) or a two-digit hexadecimal number — for example, “aa:00:04:00:1d:04” means the same as “AA-0-4-0-1D-4”. Another valid format is one of “xxxx.xxxx.xxxx” or “xxxxxxxxxxxx”, where each “x” is a hexadecimal digit — for example, “aa0004001d04”. **gateway** *host*: True if the packet used *host* as a gateway. I.e., the source or the destination Ethernet-like address is *host* but neither the source nor the destination ARP/IPv4/RARP address is *host*. This primitive is valid only for the same link-layer types as the **ether host** primitive above, also it cannot be applied to packets encapsulated in MPLS, VXLAN or Geneve. May be qualified with a specific protocol (**arp**, **ip**, **rarp**). For example, ``` ip gateway host ``` is equivalent to ``` ether host ethernameaddr and ip and not ip host hostnameaddr ``` which can be used with either names or numbers for *hostnameaddr* and *ethernameaddr*. : *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.). **net** *netnameaddr*: True if the source or the destination ARP/IPv4/IPv6/RARP address of the packet belongs to the specified network. May be qualified with a specific protocol (**arp**, **ip**, **ip6**, **rarp**) and/or a different direction (**src**, **dst**, **src and dst**), in the latter case the **net** keyword remains mandatory. *netnameaddr* may be either an IPv4 network number or an IPv6 network number or an IPv4 network name. : 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 (/32) for a dotted quad (which means that it's really a host match), 255.255.255.0 (/24) for a dotted triple, 255.255.0.0 (/16) for a dotted pair, or 255.0.0.0 (/8) for a single number. : An IPv6 network number is an IPv6 address as discussed for the **host** primitive above; the implicit netmask is ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff (/128), so in this primitive IPv6 “network” matches are really always host matches. For an actual IPv6 network match see thenet netaddr/len' primitive below. : An IPv4 network name is a name from the networks database (traditionally networks(5), in OpenBSD hosts(5), also possibly NIS, LDAP, etc.). Some operating systems do not implement a networks database, in those that do the implemented behaviour varies. For example, POSIX does not specify a format of networks(5), so the line somenet 192.168 therein can translate to either 192.168.0.0/32 or 192.168.0.0/16 depending on the implementation. In this sense, the only reliable address notation to be used with an IPv4 network name would be a dotted quad (/32), in which case it would be simpler just to use a host match with a hostname, as well as DNS. For these reasons IPv4 network names should not be used in portable applications and this form of ID may be removed from this primitive in future. net netaddr mask netmask: True if the source or the destination ARP/IPv4/RARP address of the packet belongs to netaddr with the specified netmask. May be qualified with a specific protocol (arp, ip, rarp) and/or a different direction (src, dst, src and dst), in the latter case the net keyword remains mandatory. In this implementation this primitive does not support IPv6 networks. : Both netaddr and netmask use the IPv4 network number notation described above, except the “single number” form is not valid in this primitive. For example, net 192.168 mask 255.255 is equivalent to net 192.168.0.0 mask 255.255.0.0 : The netmask can represent any 32-bit value, which is why the **net** *netaddr*/*len*' primitive below is usually a better fit for use cases that require the value to be strictly one of the 33 CIDR masks (from /0 to /32). **net** *netaddr*/*len*: True if the source or the destination ARP/IPv4/IPv6/RARP address of the packet belongs to *netaddr* where the bit-length of the network mask equals *len* (in other words, the address belongs to the specified CIDR prefix). May be qualified with a specific protocol (**arp**, **ip**, **ip6**, **rarp**) and/or a different direction (**src**, **dst**, **src and dst**), in the latter case the **net** keyword is optional. : For IPv4, *len* is an integer between 0 and 32 (both inclusive) and *netaddr* is the same as the above. For IPv6, *len* is an integer between 0 and 128 (both inclusive) and *netaddr* is an IPv6 address as discussed for the **host** primitive above. For both IPv4 and IPv6 the maximum value of *len* is equivalent to a host match and the 0 value (which implies an all-zeroes value of *netaddr*) matches any address. In the latter case this primitive reduces to matching the specified (or implied) protocols only. **port** *portnamenum*: True if the source or the destination TCP/UDP/SCTP port of an IPv4/IPv6 packet is *portnamenum*. For IPv4 this also implies that the packet is the first fragment or is not fragmented; for IPv6 this also implies that the packet does not use any extension (e.g. Routing, Fragment, Destination Options) headers. May be qualified with a specific layer 4 protocol (**tcp**, **udp**, **sctp**) or a different direction (**src**, **dst**, **src and dst**), in the latter case the **port** keyword remains mandatory. Cannot be qualified with a specific layer 3 protocol (IPv4/IPv6) in the same primitive, but can be trivially combined with other primitives to achieve the required effect, for example: ``` ip and tcp dst port 80 ``` : The *portnamenum* can be a number or a name used in /etc/services (see **services**(5)). 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). **portrange** *portnamenum1-portnamenum2*: This is a more generic form of the above: true if the port number in the packet is between *portnamenum1* and *portnamenum2* (both inclusive), everything else holds the same meaning. In this predicate *portnamenum1* and *portnamenum2* can be specified in either order. If the two values are equal, this primitive has the same effect as the **port** primitive above. **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 of protocol type *protocol*. For this primitive it does not matter whether the IPv4 packet is fragmented or not. *Protocol* can be a number or one of the names recognized by **getprotobyname**(3), for example: **ah**, **esp**, **eigrp** (only in Linux with glibc, FreeBSD, NetBSD, DragonFly BSD, MidnightBSD, macOS, and QNX), **icmp**, **igmp**, **igrp** (only in Haiku and OpenBSD), **pim**, **sctp**, **tcp**, **udp** or **vrrp**. Note that most of these example identifiers are also keywords and must be escaped via backslash (\). Note that this primitive does not chase the protocol header chain. : Typically **getprotobyname**(3) parses the */etc/protocols* file to translate protocol names to numbers, and the **getent protocols** command lists the protocols recognized by the function. This is not entirely so in AIX (which does not have the command), Haiku (which has the file at */system/data/network/protocols* and does not have the command), on Linux with musl libc (which hard-codes the list of protocols) and on hosts that use a network database to resolve protocol names to numbers (see **nsswitch.conf**(5)). If a protocol name fails to translate to a number, this version of libpcap will treat the filter expression as invalid. **carp**, **vrrp**: Abbreviations for: ``` ip proto 112 ``` **icmp**: Abbreviation for: ``` ip proto 1 ``` **igmp**: Abbreviation for: ``` ip proto 2 ``` **igrp**: Abbreviation for: ``` ip proto igrpval ``` where *igrpval* is 88 on DragonFly BSD, FreeBSD, macOS, MidnightBSD, and QNX, and 9 on all other OSes. This abbreviation should not be used in portable applications and may be removed in future. **ip6 proto** *protocol*: True if the packet is an IPv6 packet of protocol type *protocol*. Besides IPv6 packets that have *protocol* in the Next Header field of the basic header, this also matches IPv6 packets that have 44 in the Next Header field of the basic header and *protocol* in the Next Header field of the immediately following Fragment extension header. (Seeip proto' above for the meaning of protocol.) Note that the IPv6 variant of ICMP uses a different protocol number, named ipv6-icmp. Note that this primitive does not chase the protocol header chain. icmp6: Abbreviation for: ip6 proto 58 proto protocol: True if the packet is an IPv4 or IPv6 packet of protocol type protocol. (See **ip proto**' above for the meaning of *protocol*.) Note that this primitive does not chase the protocol header chain. **ah**, **esp**, **pim**, **sctp**, **tcp**, **udp**: Abbreviations for: ``` proto \protocol ``` where *protocol* is one of the above protocols. **ip6 protochain** *protocol*: True if the packet is IPv6 packet, and contains protocol header with type *protocol* in its protocol header chain. (Seeip proto' above for the meaning of protocol.) 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, and is not supported by filter engines in the kernel, so this can be somewhat slow, and may cause more packets to be dropped. ip protochain protocol: Equivalent to ip6 protochain protocol, but this is for IPv4. (See **ip proto**' above for the meaning of *protocol*.) **protochain** *protocol*: True if the packet is an IPv4 or IPv6 packet of protocol type *protocol*. (Seeip proto' above for the meaning of protocol.) Note that this primitive chases the protocol header chain. ether broadcast: True if the destination Ethernet/802.11/IPFC/ARCnet/ATM LANE/FDDI/Token Ring address of the packet is the broadcast address (e.g. FF:FF:FF:FF:FF:FF for Ethernet). The ether keyword is optional. ip broadcast: True if the packet is an IPv4 packet with the host part of the destination address being either all-ones or all-zeroes. This primitive requires to specify the netmask, which cannot be done in the filter expression; the only way to specify a netmask is via the netmask argument of the pcap_compile() function. If a netmask has not been specified, an attempt to compile a filter expression with this primitive will return an error. : Note that this primitive ignores the network part of the destination address, thus it can match more packets than expected, especially if the interface has multiple IPv4 addresses with different netmasks. For example, if the interface has addresses 10.1.2.100/29 and 192.168.202.200/24 configured and the netmask argument corresponds to the first address, its value will be 0xFFFFFFF8 and the host mask value will be 0x00000007. This will match the expected two addresses in the first prefix (10.1.2.96 and 10.1.2.103), as well as 64 addresses in the second prefix (192.168.202.0, 192.168.202.7, 192.168.202.8, 192.168.202.15, 192.168.202.16 and so on), as well as any other IPv4 address with the lowest 3 bits being all-ones or all-zeroes (for example: 10.73.74.151, 192.168.50.63, 172.19.0.128) — in other words, 25% of the complete IPv4 address space. This is why in use cases that require more precision it would be better to match the required address(es) explicitly, for example: ip dst host 10.1.2.96 or 10.1.2.103 ether multicast: True if the destination Ethernet/802.11/IPFC/ARCnet/ATM LANE/FDDI/Token Ring address of the packet is a multicast address (e.g. ether[0] & 1 != 0 for Ethernet). The ether keyword is optional. 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: : aarp: AppleTalk ARP Protocol arp: ARP atalk: AppleTalk decnet: DECNet ip: IPv4 ip6: IPv6 ipx: Novell IPX iso: OSI protocols lat: DEC Local Area Transport (LAT) lldp: Link-Layer Discovery Protocol loopback: Loopback frames (DIX Ethernet Configuration Test Protocol) mopdl: DEC DNA Dump/Load (MOP), moprc: DEC DNA Remote Console (MOP) netbeui: NetBIOS Frame Protocol rarp: Reverse ARP sca: DEC System Communication Architecture (SCA) slow: IEEE Slow Protocols, such as LACP, OAM and OSSP stp: IEEE Spanning Tree Protocol : Note these identifiers (except lldp, loopback and slow) are also keywords and must be escaped via backslash (). : [In the case of FDDI (e.g., **fddi proto \arp**'), Token Ring (e.g.,tr proto \arp'), and IEEE 802.11 wireless LANs (e.g., **wlan proto \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, the filter 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**: the filter checks the DSAP (Destination Service Access Point) and SSAP (Source Service Access Point) fields of the LLC header; **stp** and **netbeui**: the filter checks the DSAP of the LLC header; **atalk**: the filter checks for a SNAP-format packet with an OUI of 0x080007 and the AppleTalk EtherType. : In the case of Ethernet, the filter checks the EtherType field for most of those protocols. The exceptions are: : **iso**, **stp**, and **netbeui**: the filter 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 EtherType in an Ethernet frame and for a SNAP-format packet as it does for FDDI, Token Ring, and 802.11; **aarp**: the filter checks for the AppleTalk ARP EtherType in either an Ethernet frame or an 802.2 SNAP frame with an OUI of 0x000000; **ipx**: the filter checks for the IPX EtherType in an Ethernet frame, the IPX DSAP in the LLC header, the 802.3-with-no-LLC-header encapsulation of IPX, and the IPX EtherType in a SNAP frame. **ip**, **ip6**, **arp**, **rarp**, **atalk**, **aarp**, **decnet**, **iso**, **stp**, **ipx**, **netbeui**: Abbreviations for: ``` ether proto \protocol ``` where *protocol* is one of the above protocols. **lat**, **mopdl**, **moprc**, **sca**: Abbreviations for: ``` ether proto \protocol ``` where *protocol* is one of the above protocols, all of which originated at DEC, but are not the same as DECnet. **decnet host** *decnetaddr*: True if the source or the destination DECnet address of the packet is *decnetaddr*. May be qualified with a different direction (**src**, **dst**, **src and dst**), in which case the **host** keyword is optional. : *decnetaddr* is an address of the form **AREANUMBER.NODENUMBER**, where the area number can be between 0 and 63 (both inclusive) and the node number can be between 0 and 1023 (both inclusive) and both numbers always use decimal base. For example: ``` decnet src 10.123 ``` **llc**: True if the packet has an 802.2 LLC header. This includes: : Ethernet packets with a length field rather than a type field that aren't raw NetWare-over-802.3 packets; : IEEE 802.11 data packets; : Token Ring packets (no check is done for LLC frames); : FDDI packets (no check is done for LLC frames); : LLC-encapsulated ATM packets, for SunATM on Solaris. **llc** *type*: True if the packet has an 802.2 LLC header and has the specified *type*. *type* can be one of: : **i**: Information (I) PDUs **s**: Supervisory (S) PDUs **u**: Unnumbered (U) PDUs **rr**: Receiver Ready (RR) S PDUs **rnr**: Receiver Not Ready (RNR) S PDUs **rej**: Reject (REJ) S PDUs **ui**: Unnumbered Information (UI) U PDUs **ua**: Unnumbered Acknowledgment (UA) U PDUs **disc**: Disconnect (DISC) U PDUs **dm**: Disconnected Mode (DM) U PDUs **sabme**: Set Asynchronous Balanced Mode Extended (SABME) U PDUs **test**: Test (TEST) U PDUs **xid**: Exchange Identification (XID) U PDUs **frmr**: Frame Reject (FRMR) U PDUs **inbound**: True if the packet was received by the host performing the capture rather than sent by that host. This primitive is supported for certain link-layer types only, namely, **DLT\_SLIP**, **DLT\_IPNET**, **DLT\_LINUX\_SLL**, **DLT\_LINUX\_SLL2**, **DLT\_PFLOG**, **DLT\_PPP\_PPPD**, a number of Juniper Networks private types and some types of Linux DSA tag. For reference, the ``any'' pseudo-interface uses **DLT\_LINUX\_SLL** or **DLT\_LINUX\_SLL2** on Linux, and **DLT\_IPNET** on Solaris. **outbound**: Same as the above, but for the opposite direction (from the capturing host to the network). **ifindex** *interface\_index*: True if the packet was logged via the specified interface (applies only to packets logged by the Linux “any” cooked v2 interface). **ifname** *interface*: True, for **DLT\_PFLOG** only, if the packet was logged as coming from the specified interface. **on** *interface*: Synonymous with the **ifname** primitive. **rnr** *num*: True, for **DLT\_PFLOG** only, if the packet was logged as matching the specified PF rule number. **rulenum** *num*: Synonymous with the **rnr** primitive. **reason** *code*: True, for **DLT\_PFLOG** only, if the packet was logged with the specified PF reason code. Valid codes are: **match**, **bad-offset**, **fragment**, **short**, **normalize**, **memory**, **bad-timestamp**, **congestion**, **ip-option**, **proto-cksum**, **state-mismatch**, **state-insert**, **state-limit**, **src-limit**, **synproxy**, **map-failed** (on FreeBSD only), **state-locked** (on NetBSD only), **translate** (on OpenBSD only), **no-route** (on OpenBSD only) and **dummynet** (on macOS only). **rset** *name*: True, for **DLT\_PFLOG** only, if the packet was logged as matching the specified PF ruleset name of an anchored ruleset. **ruleset** *name*: Synonymous with the **rset** primitive. **srnr** *num*: True, for **DLT\_PFLOG** only, if the packet was logged as matching the specified PF rule number of an anchored ruleset. **subrulenum** *num*: Synonymous with the **srnr** primitive. **action** *act*: True, for **DLT\_PFLOG** only, if PF took the specified action when the packet was logged. Valid actions are: **pass** (or **accept**), **block** (or **drop**) and, with later versions of **pf**(4), **scrub**, **noscrub**, **nat**, **nonat**, **binat**, **nobinat**, **rdr**, **nordr**, **synproxy-drop**, **defer** (on FreeBSD and OpenBSD only), **match** (on OpenBSD only), **divert** (on OpenBSD only), **rt** (on OpenBSD only), **afrt** (on OpenBSD only), **dummynet** (on macOS only), **nodummynet** (on macOS only), **nat64** (on macOS only) and **nonat64** (on macOS only). **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. **wlan type** *wlan\_type*: True if the IEEE 802.11 frame type matches the specified *wlan\_type*. Valid *wlan\_type*s are: **mgt**, **ctl** and **data**. The **wlan** keyword is optional. **wlan type** *wlan\_type* **subtype** *wlan\_subtype*: True if the IEEE 802.11 frame type matches the specified *wlan\_type* and frame subtype matches the specified *wlan\_subtype*. The **wlan** keyword is optional. : If the specified *wlan\_type* is **mgt**, then valid *wlan\_subtype*s are: **assoc-req**, **assoc-resp**, **reassoc-req**, **reassoc-resp**, **probe-req**, **probe-resp**, **beacon**, **atim**, **disassoc**, **auth** and **deauth**. : If the specified *wlan\_type* is **ctl**, then valid *wlan\_subtype*s are: **bar**, **ba**, **ps-poll**, **rts**, **cts**, **ack**, **cf-end** and **cf-end-ack**. : If the specified *wlan\_type* is **data**, then valid *wlan\_subtype*s are: **data**, **data-cf-ack**, **data-cf-poll**, **data-cf-ack-poll**, **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**. **wlan 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. The **wlan** keyword is optional. **wlan dir** *direction*: True if the IEEE 802.11 frame direction matches the specified *direction*. Valid directions are: **nods**, **tods**, **fromds**, **dstods**, or a numeric value. The **wlan** keyword is optional. **vlan** *[vlan\_id]*: True if the packet is an IEEE 802.1Q VLAN packet. If the optional *vlan\_id* is specified, only true if the packet has the specified *vlan\_id*. Note that the first **vlan** keyword encountered in an expression changes the decoding offsets for the remainder of the expression on the assumption that the packet is a VLAN packet. Thevlan[vlan_id]keyword may be used more than once, to filter on VLAN hierarchies. Each use of that keyword increments the filter offsets by 4. : For example: ``` vlan 100 && vlan 200 ``` filters on VLAN 200 encapsulated within VLAN 100, and ``` vlan && vlan 300 && ip ``` filters IPv4 protocol encapsulated in VLAN 300 encapsulated within any higher order VLAN. **mpls** *[label\_num]*: True if the packet is an MPLS packet. If the optional *label\_num* is specified, only true if the packet has the specified *label\_num*. Note that the first **mpls** keyword encountered in an expression changes the decoding offsets for the remainder of the expression on the assumption that the packet is a MPLS-encapsulated IP packet. Thempls [label_num]eyword may be used more than once, to filter on MPLS hierarchies. Each use of that keyword increments the filter 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 (EtherType 0x8863). **pppoes** *[session\_id]*: True if the packet is a PPP-over-Ethernet Session packet (EtherType 0x8864). If the optional *session\_id* is specified, only true if the packet has the specified *session\_id*. Note that the first **pppoes** keyword encountered in an expression changes the decoding offsets for the remainder of the expression on the assumption that the packet is a PPPoE session packet. : For example: pppoes 0x27 && ip filters IPv4 protocol encapsulated in PPPoE session id 0x27. **geneve** *[vni]*: True if the packet is a Geneve packet (UDP port 6081). If the optional *vni* is specified, only true if the packet has the specified *vni*. Note that when the **geneve** keyword is encountered in an expression, it changes the decoding offsets for the remainder of the expression on the assumption that the packet is a Geneve packet. : For example: geneve 0xb && ip filters IPv4 protocol encapsulated in Geneve with VNI 0xb. This will match both IPv4 directly encapsulated in Geneve as well as IPv4 contained inside an Ethernet frame. **vxlan** *[vni]*: True if the packet is a VXLAN packet (UDP port 4789). If the optional *vni* is specified, only true if the packet has the specified *vni*. Note that when the **vxlan** keyword is encountered in an expression, it changes the decoding offsets for the remainder of the expression on the assumption that the packet is a VXLAN packet. : For example: vxlan 0x7 && ip6 filters IPv6 protocol encapsulated in VXLAN with VNI 0x7. **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 \protocol where *protocol* is one of the above protocols. Also in this context **es-is** is an alias for **esis** and **is-is** is an alias for **isis**. **isis proto** *protocol*: True if the packet is an IS-IS packet of protocol type *protocol*, which can be a number only. **l1**, **l2**, **iih**, **lsp**, **snp**, **csnp**, **psnp**: Abbreviations for IS-IS PDU types. *atmfield relop val*: True if the packet is an ATM packet, for SunATM on Solaris, and the relation holds. *atmfield* is one of {**vpi**, **vci**}; *relop* is one of {**>**, **<**, **>=**, **<=**, **=**, **==**, **!=**} (where **=** means the same as **==**); *val* is an integer. **vpi** and **vci** stand for the virtual path identifier (VPI) and the virtual channel identifier (VCI) fields respectively. *atmfield* *val*: Abbreviation for atmfield == val in the expression above. *atmfield* (*val1* **or** ... **or** *valN*): Abbreviation for (atmfield == val1 or ... or atmfield == valN) in the expression above. **lane**: True if the packet is an ATM packet, for SunATM on Solaris, and is an ATM LANE packet. Note that the first **lane** keyword encountered in an expression changes the tests done in the remainder of the 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. : Also the first **lane** keyword enables primitives that do not apply to ATM in general, such as **link host** and **link multicast**. **oamf4sc**: True if the packet is an ATM packet, for SunATM on Solaris, and is a segment OAM F4 flow cell (VPI=0 & VCI=3). **oamf4ec**: True if the packet is an ATM packet, for SunATM on Solaris, and is an end-to-end OAM F4 flow cell (VPI=0 & VCI=4). **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 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)). **metac**: True if the packet is an ATM packet, for SunATM on Solaris, and is on a meta signaling circuit (VPI=0 & VCI=1). **bcc**: True if the packet is an ATM packet, for SunATM on Solaris, and is on a broadcast signaling circuit (VPI=0 & VCI=2). **sc**: True if the packet is an ATM packet, for SunATM on Solaris, and is on a signaling circuit (VPI=0 & VCI=5). **ilmic**: True if the packet is an ATM packet, for SunATM on Solaris, and is on an ILMI circuit (VPI=0 & VCI=16). **connectmsg**: True if the packet is an ATM packet, for SunATM on Solaris, and is on a signaling circuit and is a Q.2931 Setup, Call Proceeding, Connect, Connect Ack, Release, or Release Done message. **metaconnect**: True if the packet is an ATM packet, for SunATM on Solaris, and is on a meta signaling circuit and is a Q.2931 Setup, Call Proceeding, Connect, Release, or Release Done message. **fisu**: True if the packet is a Fill-In Signal Unit (FISU) MTP2 packet. **lssu**: True if the packet is a Link Status Signal Unit (LSSU) MTP2 packet. **msu**: True if the packet is a Message Signal Unit (MSU) MTP2 packet. *mtpfield relop val*: True if the relation holds. *mtpfield* is one of {**sio**, **dpc**, **opc**, **sls**}; *relop* is one of {**>**, **<**, **>=**, **<=**, **=**, **==**, **!=**} (where **=** means the same as **==**); *val* is an integer. **sio** stands for the Service Information Octet (SIO) field of the MTP2 MSU header. **dpc**, **opc** and **sls** stand for the Destination Point Code (DPC), Originating Point Code (OPC) and Signalling Link Selection (SLS) fields respectively of the MTP3 standard routing label. *mtpfield* *val*: Abbreviation for mtpfield == val in the expression above. *mtpfield* (*val1* **or** ... **or** *valN*): Abbreviation for (mtpfield == val1 or ... or mtpfield == valN) in the expression above. **hfisu**, **hlssu**, **hmsu**, **hsio**, **hdpc**, **hopc**, **hsls**: Same as **fisu**, **lssu**, **msu**, **sio**, **dpc**, **opc** and **sls** respectively, but only if the MTP2 link uses the extended sequence numbers encoding specified for high speed signalling links (HSL) in ITU-T Recommendation Q.703 Annex A. **link host** *mac8addr*: True if the source or the destination ARCnet node ID (for **DLT\_ARCNET** and **DLT\_ARCNET\_LINUX** only) or MS/TP station address (for **DLT\_BACNET\_MS\_TP** only) is *mac8addr*. May be qualified with a different direction (**src**, **dst**, **src and dst**), in which case the **host** keyword is optional. : *mac8addr* is a string of the form **$xx** or **$x**, where “x” is a hexadecimal digit. For example: link host $2b ``` : Also in ARCnet context broadcast and multicast are equivalent to link dst $0, and in MS/TP context broadcast is equivalent to link dst $ff. : Note that this address syntax clashes with the parameter expansion syntax in POSIX-compatible shells and elsewhere, so depending on the use case the filter string may require the use of single quotes or a backslash. byte idx op val: True if the value of the link layer byte number idx satisfies a condition with regard to val, which can be a number only. The condition is one of: “equals to” (if op is =), “less than” (if op is <), “greater than” (if op is >), “the result of bitwise AND is not zero” (if op is &), “the result of bitwise OR is not zero” (if op is |). : The arithmetic expressions and packet data accessors below implement all of these and many other things much better, so this primitive will be removed in a future release and should not be used in applications that require forward compatibility.

ARITHMETIC EXPRESSIONS

Arithmetic expressions are the operands of a relational operator in a relation of the following form:

expr1 relop expr2

This evaluates to true if and only if the relation holds. relop (the relational operator) is one of {>, <, >=, <=, =, ==, !=} (where = means the same as ==). Each of expr1 and expr2 is an arithmetic expression composed of integer constants (expressed in standard C syntax), the common arithmetic and bitwise binary operations {+, -, *, /, %, &, |, ^, <<, >>}, parentheses, the negative of any arithmetic expression (using unary - and defined as the expression subtracted from zero), a length accessor, and packet data accessors. All arithmetic expressions regardless of the complexity and composition resolve to an integer value. Note that in a filter program all integer values are 32-bit unsigned, so that, for example, both 0x80000000 and 0xffffffff are > 0, and -1 is a synonym for 0xffffffff.

Note that 32-bit octal integer constants in the [010000000000 .. 037777777777] interval, which includes 75% of all 32-bit integers, are interpreted as MAC-48 addresses when prepended with a single zero (e.g., 012345670123 means 01:23:45:67:01:23). To disambiguate the expression, prepend such an octal number with more zeroes (0012345670123) or represent the same value using a decimal (1402433619) or hexadecimal (0x53977053) number.

The modulo (%) and bitwise XOR (^) operators are currently only supported for filtering in the kernel on particular operating systems (for example: FreeBSD 12.0 and later, Linux with 3.7 and later kernels, NetBSD 8.0 and later, OpenBSD 7.9 and later, Windows with Npcap 1.81 and later); on all other systems (for example: AIX, Hurd, illumos, Solaris), if those operators are used, filtering will be done in user mode, which will increase the overhead of capturing packets and may cause more packets to be dropped.

The length accessor, indicated by the keywords len or length, gives the length of the packet.

PACKET DATA ACCESSORS

To use the packet data in an arithmetic expression, use the following syntax:

proto [ expr : size ]

Proto is one of arp, atalk, carp, decnet, ether, fddi, icmp, icmp6, igmp, igrp, ip, ip6, lat, link, mopdl, moprc, pim, ppp, radio, rarp, sca, sctp, slip, tcp, tr, udp, vrrp or wlan, and indicates the protocol layer for the index operation. (ether, fddi, link, ppp, slip, tr and wlan all refer to the link layer, radio refers to the “radio header” added to some 802.11 captures.)

Note that in the current implementation of packet data accessors the tcp, udp, icmp, igmp, pim, vrrp, carp, sctp and igrp above do not match IPv6 packets (this may be fixed for some of these protocols in future), also the icmp6 above implies that the IPv6 packet does not have any extension (e.g. Fragment) headers, also the igrp above uses an OS-specific protocol number (as discussed for the igrp abbreviation earlier) and therefore should not be used in portable applications and may be removed in future.

The byte offset, relative to the indicated protocol layer, is given by expr, which can be an integer constant or any other valid arithmetic expression. 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; also it must be one of these valid integer constants only and cannot be a more complex expression.

For example, **ether[**0**] &** 1 **!=** 0' catches all multicast traffic. The expressionip[0] & 0xf != 5' catches all IPv4 packets with options. The expression `ip[6:2] & 0x1fff = 0' catches only unfragmented IPv4 datagrams and the first fragment of fragmented IPv4 datagrams. This check is implicitly applied to the tcp, udp, icmp, sctp, igmp, pim, igrp, vrrp and carp 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.

NAMED VALUES

Some offsets and field values may be expressed as names rather than as numeric values. The following protocol header field offsets are available: icmptype (ICMP type field), icmp6type (ICMPv6 type field), icmpcode (ICMP code field), icmp6code (ICMPv6 code field) and tcpflags (TCP flags field).

The following ICMP type field values are available: 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.

The following ICMPv6 type field values are available: icmp6-destinationunreach, icmp6-packettoobig, icmp6-timeexceeded, icmp6-parameterproblem, icmp6-echo, icmp6-echoreply, icmp6-multicastlistenerquery, icmp6-multicastlistenerreportv1, icmp6-multicastlistenerdone, icmp6-routersolicit, icmp6-routeradvert, icmp6-neighborsolicit, icmp6-neighboradvert, icmp6-redirect, icmp6-routerrenum, icmp6-nodeinformationquery, icmp6-nodeinformationresponse, icmp6-ineighbordiscoverysolicit, icmp6-ineighbordiscoveryadvert, icmp6-multicastlistenerreportv2, icmp6-homeagentdiscoveryrequest, icmp6-homeagentdiscoveryreply, icmp6-mobileprefixsolicit, icmp6-mobileprefixadvert, icmp6-certpathsolicit, icmp6-certpathadvert, icmp6-multicastrouteradvert, icmp6-multicastroutersolicit, icmp6-multicastrouterterm.

The following TCP flags field values are available: tcp-fin, tcp-syn, tcp-rst, tcp-push, tcp-ack, tcp-urg, tcp-ece, tcp-cwr.

COMPOUND EXPRESSIONS

Primitives and relations may be combined using:

Parentheses.

Negation (**!**' ornot').

Concatenation (**&&**' orand').

Alternation (**||**' oror').

Negation has the highest precedence. Alternation and concatenation have equal precedence and associate left to right.

For primitives, 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 and host ace)

PROTOCOL NAMES IN VARIOUS CONTEXTS

The table below shows which protocol names can be used in which contexts of the currently implemented syntax. The “name” column contains a protocol name, which can be used as a keyword and/or as an ID for the proto case of the type qualifier kind.

For keywords: if the keyword is an alias, the “K/see” column refers to the main keyword; the “K/abbr” column tells whether the keyword can be used as an abbreviation (that is, if the keyword is the only contents of a primitive, it means a more complex expression); the “K/PDA” column tells whether the keyword can be used in a packet data accessor; the “K/pqual” column tells whether the keyword can be used as a case of the proto qualifier kind.

For IDs: the “ID/tqual” column shows the valid context(s).

EXAMPLES

To select all packets arriving at or departing from `sundown':

: host sundown

To select traffic between helios' and eitherhot' or `ace':

: host helios and (hot or ace)

To select all IPv4 packets between ace' and any host excepthelios':

: 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 IPv4 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 the TCP packets with flags RST and ACK both set. (i.e. select only the RST and ACK flags in the flags field, and if the result is “RST and ACK both set”, match)

: tcp[tcpflags] & (tcp-rst|tcp-ack) == (tcp-rst|tcp-ack)

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 IPv4 packets longer than 576 bytes sent through gateway `snup':

: gateway snup and ip[2:2] > 576

To select IPv4 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 icmp6[icmp6type] != icmp6-echo and icmp6[icmp6type] != icmp6-echoreply

BACKWARD COMPATIBILITY

The carp keyword became available in libpcap 1.2.1.

The hfisu, hlssu, hmsu, hsio, hopc, hdpc and hsls keywords became available in libpcap 1.5.3.

The modulo (%) and bitwise XOR (^) binary operators became available in libpcap 1.6.2.

The geneve keyword became available in libpcap 1.8.0.

The ICMPv6 type code names, as well as the tcp-ece and tcp-cwr TCP flag names became available in libpcap 1.9.0.

The ifindex keyword became available in libpcap 1.10.0.

The vxlan keyword became available in libpcap 1.11.0.

The lldp and slow protocols became available for “ether proto” in libpcap 1.11.0.

Before libpcap 1.11.0 the gateway primitive had a different definition, which did not produce the expected results, also its support was conditional and since libpcap 1.0.0 was disabled by default.

SEE ALSO

pcap(3PCAP)

BUGS

To report a security issue please send an e-mail to security@tcpdump.org.

To report bugs and other problems, contribute patches, request a feature, provide generic feedback etc please see the file CONTRIBUTING.md in the libpcap source tree root.

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. For example, to match IPv6 fragments: `ip6 protochain 44'

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

The sio and hsio keywords do not test whether the packet is an MSU packet. The dpc, opc, sls, hdpc, hopc and hsls keywords do not test whether the packet is an MTP3 packet.

For ARP and RARP the current implementation assumes IPv4 over Ethernet and may incorrectly match packets that have a different combination of protocol and hardware.

Index

NAME: DESCRIPTION: PRIMITIVES: ARITHMETIC EXPRESSIONS: PACKET DATA ACCESSORS: NAMED VALUES: COMPOUND EXPRESSIONS: PROTOCOL NAMES IN VARIOUS CONTEXTS: EXAMPLES: BACKWARD COMPATIBILITY: SEE ALSO: BUGS

COLOPHON

This HTML man page was generated at 09:16:51 GMT, September 17, 2026 from a source man page in “The Tcpdump Group” git repositories using man2html and other tools.