pcap-filter(7) man page | TCPDUMP & LIBPCAP (original) (raw)

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This man page documents libpcap version 1.11.0-PRE-GIT (see also: 1.10.5, 1.10.4, 1.10.2, 1.10.1, 1.10.0, 1.9.1, 1.8.1, 1.7.4, 1.6.2, 1.5.3).

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.

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 topcap_loop(3PCAP),pcap_dispatch(3PCAP),pcap_next(3PCAP), orpcap_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 theprototype qualifier below.) Possible protocols are:ether,link,wlan,ip,ip6,arp,tcp,udp,sctp,iso,isis,rarp,decnet,fddi,tr,pppandslip. 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' 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 aresrc,dst,src or dst,src and dst,ra,ta,addr1,addr2,addr3, andaddr4. 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. Thera**,ta,addr1,addr2,addr3, andaddr4qualifiers 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 arehost,net,proto,port,portrange,protochainandgateway.E.g., `**host** foo', `net 128.3', `**port** 20', `portrange 6000-6008', `proto 17'. If there is no type qualifier,hostis 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 hostand 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 thelink,pppandslipkeywords.]

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 wordsand,orandnot(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 thehostkeyword 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 address or a name. If it is an IPv6 address, it may use both the zero compression (::) and the IPv4-mapped (x:x:x:x:x:x:d.d.d.d) notations as discussed ininet_pton(3). If it is a name, the name must resolve to at least one IPv4 address forarp host,ip hostandrarp host, at least one IPv6 address forip6 hostand at least one IPv4/IPv6 address forhost.

When not qualified with a protocol, this primitive matches all protocols that make sense for the address families of the specified/resolved addresses. For example, for a name that resolves only to an IPv6 addressarp hostreturns an error, buthostis valid and means IPv6; likewise, for a name that resolves only to an IPv4 addressip6 hostreturns an error, buthostis valid and means ARP/IPv4/RARP.

Whether qualified with a protocol or not, this primitive evaluates to true if the name resolves to more than one address and at least one of the addresses matches the packet.

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 thehostkeyword is optional.

_ethernameaddr_may be either a name from /etc/ethers or a numerical MAC address of the form "xx:xx:xx:xx:xx:xx", "xx.xx.xx.xx.xx.xx", "xx-xx-xx-xx-xx-xx", "xxxx.xxxx.xxxx" or "xxxxxxxxxxxx", where each "x" is a hex digit (0-9, a-f, or A-F).

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 theether hostprimitive above. May be qualified with a specific protocol (arp,ip,rarp). For example,

ip gateway host

is equivalent to

ether host ethernameaddr 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 thenetkeyword remains mandatory._netnameaddr_may be either a name from the networks database (/etc/networks, etc.) or a network number.

An IPv4 network number can be written as a dotted quad (e.g., 192.168.1.0), dotted triple (e.g., 192.168.1), dotted pair (e.g, 172.16), or single number (e.g., 10); the netmask is 255.255.255.255 (/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 thehostprimitive 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 the `net netaddr/len' primitive below.

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 thenetkeyword 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 thenetkeyword 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 thehostprimitive 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. 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 theportkeyword 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 (seeservices(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 theportprimitive 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.Protocol can be a number or one of the names recognized bygetprotobyname(3), for example:ah,esp,eigrp(only in Linux with glibc, FreeBSD, NetBSD, DragonFly BSD, and macOS),icmp,igmp,igrp(only in Haiku and OpenBSD),pim,sctp,tcp,udporvrrp. 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.

Typicallygetprotobyname(3) parses the_/etc/protocols_file to translate protocol names to numbers, and thegetent protocolscommand 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 (seensswitch.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 and macOS, 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. (See `ip proto' above for the meaning of protocol.) Note that the IPv6 variant of ICMP uses a different protocol number, namedipv6-icmpin AIX, FreeBSD, illumos, Haiku, GNU/Hurd, Linux, macOS, NetBSD, OpenBSD, Solaris and Windows. 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, 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_. (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 address (e.g.FF:FF:FF:FF:FF:FFfor Ethernet). Theetherkeyword 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 thenetmaskargument of thepcap_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 thenetmaskargument corresponds to the first address, its value will be0xFFFFFFF8and the host mask value will be0x00000007. 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 != 0for Ethernet). Theetherkeyword 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 thehostkeyword is optional.

_decnetaddr_is an address of the formAREANUMBER.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 usesDLT_LINUX_SLLorDLT_LINUX_SLL2on Linux, andDLT_IPNETon 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, forDLT_PFLOGonly, if the packet was logged as coming from the specified interface.

on interface

Synonymous with theifnameprimitive.

rnr num

True, forDLT_PFLOGonly, if the packet was logged as matching the specified PF rule number.

rulenum num

Synonymous with thernrprimitive.

reason code

True, forDLT_PFLOGonly, 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) anddummynet(on macOS only).

rset name

True, forDLT_PFLOGonly, if the packet was logged as matching the specified PF ruleset name of an anchored ruleset.

ruleset name

Synonymous with thersetprimitive.

srnr num

True, forDLT_PFLOGonly, if the packet was logged as matching the specified PF rule number of an anchored ruleset.

subrulenum num

Synonymous with thesrnrprimitive.

action act

True, forDLT_PFLOGonly, if PF took the specified action when the packet was logged. Valid actions are:pass(oraccept),block(ordrop) and, with later versions ofpf(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) andnonat64(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,ctland data. Thewlankeyword 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. Thewlankeyword 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 anddeauth.

If the specified wlan_type is ctl, then valid _wlan_subtype_s are:bar,ba,ps-poll,rts,cts,ack,cf-end andcf-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-pollandqos-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. Thewlankeyword 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. Thewlankeyword 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. 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_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. 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 (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 namesclnp, esis, or isis.

clnp, esis, isis

Abbreviations for:

*iso proto *protocol

where protocol is one of the above protocols. Also in this contextes-isis an alias foresisandis-isis an alias forisis.

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.vpiandvcistand 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 firstlanekeyword enables primitives that do not apply to ATM in general, such aslink hostandlink 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.siostands for the Service Information Octet (SIO) field of the MTP2 MSU header.dpc,opcandslsstand 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 asfisu,lssu,msu,sio,dpc,opcandslsrespectively, 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 (forDLT_ARCNETandDLT_ARCNET_LINUXonly) or MS/TP station address (forDLT_BACNET_MS_TPonly) is_mac8addr_. May be qualified with a different direction (src,dst,src and dst), in which case thehostkeyword is optional.

_mac8addr_is a string of the form**$xxor$x**, where "x" is a hexadecimal digit. For example:

link host $2b

Also in ARCnet contextbroadcastandmulticastare equivalent tolink dst 0∗∗,andinMS/TPcontext∗∗broadcast∗∗isequivalentto∗∗linkdst0, and in MS/TP contextbroadcastis equivalent tolink dst 0∗∗,andinMS/TPcontext∗∗broadcast∗∗isequivalentto∗∗linkdstff.

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 {**+**,**-**,*****,**/**,**%**,**&**,**|**,**^**,**<<**,**>>}, a length operator, and packet data accessors. All arithmetic 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 expression, 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 operator, indicated by the keyword len, 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 ofarp,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,vrrporwlan, and indicates the protocol layer for the index operation. (ether,fddi,link,ppp,slip,trandwlanall refer to the link layer, radio refers to the "radio header" added to some 802.11 captures.) Note that tcp, udp and other upper-layer protocol types only apply to IPv4, not IPv6 (this will be fixed in the future). The byte offset, relative to the indicated protocol layer, is given by expr, 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 expression `ip[0] &** 0xf != 5' catches all IPv4 packets with options. The expression `ip[6:2] & 0x1fff = 0' catches only unfragmented IPv4 datagrams and frag zero of fragmented IPv4 datagrams. This check is implicitly applied to thetcp,udp,icmp,sctp,igmp,pim,igrp,vrrpandcarpindex 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) andtcpflags (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 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 theprotocase 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 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. 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

Thecarpkeyword became available in libpcap 1.2.1.

Thehfisu,hlssu,hmsu,hsio,hopc,hdpcandhslskeywords became available in libpcap 1.5.3.

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

Thegenevekeyword became available in libpcap 1.8.0.

The ICMPv6 type code names, as well as thetcp-eceandtcp-cwrTCP flag names became available in libpcap 1.9.0.

Theifindexkeyword became available in libpcap 1.10.0.

Thevxlankeyword became available in libpcap 1.11.0.

Thelldpandslowprotocols became available for "ether proto" in libpcap 1.11.0.

SEE ALSO

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.

Thesioandhsiokeywords do not test whether the packet is an MSU packet. Thedpc,opc,sls,hdpc,hopcandhslskeywords 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 13:05:55 GMT, November 23, 2025 from a source man page in "The Tcpdump Group" git repositories using man2html and other tools.