+----------------------------------------------------------------------------+ | | | This man page documents libpcap version 1.11.0-PRE-GIT. | | | | Your system may have a different version installed, possibly with some | | local modifications. To achieve the best results, please make sure this | | version of this man page suits your needs. If necessary, try to look for | | a different version on this web site or in the man pages available in your | | installation. | | | +----------------------------------------------------------------------------+ PCAP-FILTER(7) Miscellaneous Information Manual PCAP-FILTER(7) 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 be- low.) 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 proto- cols 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' and `port 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 Wire- less 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 com- binations 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 combina- tions 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 identi- cally 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 ex- plicitly 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, in- bound, 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 as `tcp 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 op- tional. 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 net- work 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 toler- ates an optional "/128" after an IPv6 host number, this behav- iour 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 for `ip6 host', and at least one IPv4/IPv6 address for `host'. If the name resolves to more than one address, this primitive eval- uates 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 speci- fied/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 address `arp host' returns an error, but `host' is valid and means IPv6, for a name that resolves only to an IPv4 address `ip6 host' returns an error, but `host' is valid and means ARP/IPv4/RARP, for a name that resolves to both IPv4 and IPv6 addresses `ip 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 hexa- decimal 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-ad- dress 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 quali- fied with a specific protocol (arp, ip, ip6, rarp) and/or a dif- ferent 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 prim- itive IPv6 "network" matches are really always host matches. For an actual IPv6 network match see the `net netaddr/len' prim- itive below. An IPv4 network name is a name from the networks database (tra- ditionally 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 implementa- tion. 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 op- tional. 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 inte- ger 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 ne- taddr) 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 exten- sion (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 primi- tive, 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 num- ber 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 ei- ther 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, 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, 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 exten- sion header. (See `ip proto' above for the meaning of proto- col.) Note that the IPv6 variant of ICMP uses a different pro- tocol 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. (See `ip 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, authentica- tion header, routing header, or hop-by-hop option header, be- tween IPv6 header and TCP header. The BPF code emitted by this primitive is complex and cannot be optimized by the BPF opti- mizer code, and is not supported by filter engines in the ker- nel, 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. (See `ip 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 ad- dress (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 desti- nation 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 sec- ond 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 ad- dress (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 Pro- tocol) 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 ei- ther 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 orig- inated 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 direc- tion (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 cap- ture 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 So- laris. outbound Same as the above, but for the opposite direction (from the cap- turing host to the network). ifindex interface_index True if the packet was logged via the specified interface (ap- plies only to packets logged by the Linux "any" cooked v2 inter- face). 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 Distri- bution System) frames. wlan type wlan_type True if the IEEE 802.11 frame type matches the specified wlan_type. Valid wlan_types 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_subtypes 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_subtypes are: bar, ba, 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-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 op- tional 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. The `vlan [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 la- bel_num. Note that the first mpls keyword encountered in an ex- pression changes the decoding offsets for the remainder of the expression on the assumption that the packet is a MPLS-encapsu- lated IP packet. The `mpls [label_num]` keyword 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 (Ether- Type 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 as- sumption 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 spec- ified 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 op- tional vni is specified, only true if the packet has the speci- fied 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 con- text 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 identi- fier (VPI) and the virtual channel identifier (VCI) fields re- spectively. 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 encoun- tered 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 Proceed- ing, 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 Pro- ceeding, 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 re- spectively 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 encod- ing 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 hexa- decimal 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 expan- sion syntax in POSIX-compatible shells and elsewhere, so depend- ing 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 im- plement 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 {+, -, *, /, %, &, |, ^, <<, >>}, a length accessor, and packet data accessors. All arith- metic expressions regardless of the complexity and composition resolve to an integer value. Note that all comparisons are unsigned, so that, for example, both 0x80000000 and 0xffffffff are > 0. 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 ex- pression, prepend such an octal number with more zeroes (0012345670123) or represent the same value using a decimal (1402433619) or hexadecimal (0x53977053) number. The % and ^ operators are currently only supported for filtering in the kernel on particular operating systems (for example: FreeBSD, Linux with 3.7 and later kernels, NetBSD); on all other systems (for example: AIX, Hurd, illumos, Solaris, OpenBSD), 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 ex- tension (e.g. Fragment) headers, also the igrp above uses an OS-spe- cific 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 can- not be a more complex expression. 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 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 avail- able: icmptype (ICMP type field), icmp6type (ICMPv6 type field), icmp- code (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 (`!' or `not'). Concatenation (`&&' or `and'). Alternation (`||' or `or'). 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 con- texts 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). +---------+-------+--------+-------+---------+----------------------+ |name | K/see | K/abbr | K/PDA | K/pqual | ID/tqual | +---------+-------+--------+-------+---------+----------------------+ |aarp | | yes | no | no | link proto \aarp | |ah | | yes | no | no | [ip|ip6] proto \ah | |arp | | yes | yes | yes | link proto \arp | |atalk | | yes | yes | no | link proto \atalk | |carp | | yes | yes | no | ip proto \carp | |clnp | | yes | no | no | iso proto \clnp | |csnp | | yes | no | no | | |decnet | | yes | yes | yes | link proto \decnet | |esis | | yes | no | no | iso proto \esis | |es-is | esis | | | | | |esp | | yes | no | no | [ip|ip6] proto \esp | |ether | link | | | | | |fddi | link | | | | | |icmp | | yes | yes | no | ip proto \icmp | |icmp6 | | yes | yes | no | | |igmp | | yes | yes | no | ip proto \igmp | |igrp | | yes | yes | no | ip proto \igrp | |iih | | yes | no | no | | |ip | | yes | yes | yes | link proto \ip | |ip6 | | yes | yes | yes | link proto \ip6 | |ipx | | yes | no | no | link proto \ipx | |isis | | yes | no | yes | iso proto \isis | |is-is | isis | | | | | |iso | | yes | no | yes | link proto \iso | |l1 | | yes | no | no | | |l2 | | yes | no | no | | |lat | | yes | yes | no | link proto \lat | |link | | no | yes | yes | | |lldp | | | | | link proto lldp | |loopback | | | | | link proto loopback | |lsp | | yes | no | no | | |mopdl | | yes | yes | no | link proto \mopdl | |moprc | | yes | yes | no | link proto \moprc | |netbeui | | yes | no | no | link proto \netbeui | |pim | | yes | yes | no | [ip|ip6] proto \pim | |ppp | link | | | | | |psnp | | yes | no | no | | |radio | | no | yes | no | | |rarp | | yes | yes | yes | link proto \rarp | |sca | | yes | yes | no | link proto \sca | |sctp | | yes | yes | yes | [ip|ip6] proto \sctp | |slip | link | | | | | |slow | | | | | link proto slow | |snp | | yes | no | no | | |stp | | yes | no | no | link proto \stp | |tcp | | yes | yes | yes | [ip|ip6] proto \tcp | |tr | link | | | | | |udp | | yes | yes | yes | [ip|ip6] proto \udp | |vrrp | | yes | yes | no | ip proto \vrrp | |wlan | link | | | | | +---------+-------+--------+-------+---------+----------------------+ 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 IPv4 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 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. se- lect 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 libp- cap 1.11.0. 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 fea- ture, 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. 19 March 2026 PCAP-FILTER(7)