tc-flow(8) — Linux manual page


Flow filter in tc(8)              Linux             Flow filter in tc(8)

NAME         top

       flow - flow based traffic control filter

SYNOPSIS         top

       Mapping mode:

              tc filter ... flow map key KEY [ OPS ] [ OPTIONS ]

       Hashing mode:

              tc filter ... flow hash keys KEY_LIST [ perturb secs ] [
                      OPTIONS ]

       OPS := [ OPS ] OP

       OPTIONS := [ divisor NUM ] [ baseclass ID ] [ match EMATCH_TREE ]
               [ action ACTION_SPEC ]

       KEY_LIST := [ KEY_LIST ] KEY

       OP := { or | and | xor | rshift | addend } NUM

       ID := X:Y

       KEY := { src | dst | proto | proto-src | proto-dst | iif |
               priority | mark | nfct | nfct-src | nfct-dst | nfct-
               proto-src | nfct-proto-dst | rt-classid | sk-uid | sk-gid
               | vlan-tag | rxhash }

DESCRIPTION         top

       The flow classifier is meant to extend the SFQ hashing
       capabilities without hard-coding new hash functions. It also
       allows deterministic mappings of keys to classes.

OPTIONS         top

       action ACTION_SPEC
              Apply an action from the generic actions framework on
              matching packets.

       baseclass ID
              An offset for the resulting class ID.  ID may be root,
              none or a hexadecimal class ID in the form [X:]Y. X must
              match qdisc's/class's major handle (if omitted, the
              correct value is chosen automatically). If the whole
              baseclass is omitted, Y defaults to 1.

       divisor NUM
              Number of buckets to use for sorting into. Keys are
              calculated modulo NUM.

       hash keys KEY-LIST
              Perform a jhash2 operation over the keys in KEY-LIST, the
              result (modulo the divisor if given) is taken as class ID,
              optionally offset by the value of baseclass.  It is
              possible to specify an interval (in seconds) after which
              jhash2's entropy source is recreated using the perturb

       map key KEY
              Packet data identified by KEY is translated into class IDs
              to push the packet into. The value may be mangled by OPS
              before using it for the mapping. They are applied in the
              order listed here:

              and NUM
                  Perform bitwise AND operation with numeric value NUM.

              or NUM
                  Perform bitwise OR operation with numeric value NUM.

              xor NUM
                  Perform bitwise XOR operation with numeric value NUM.

              rshift NUM
                  Shift the value of KEY to the right by NUM bits.

              addend NUM
                  Add NUM to the value of KEY.

              For the or, and, xor and rshift operations, NUM is assumed
              to be an unsigned, 32bit integer value. For the addend
              operation, NUM may be much more complex: It may be
              prefixed by a minus ('-') sign to cause subtraction
              instead of addition and for keys of src, dst, nfct-src and
              nfct-dst it may be given in IP address notation. See below
              for an illustrating example.

       match EMATCH_TREE
              Match packets using the extended match infrastructure. See
              tc-ematch(8) for a detailed description of the allowed
              syntax in EMATCH_TREE.

KEYS         top

       In mapping mode, a single key is used (after optional
       permutation) to build a class ID. The resulting ID is deducible
       in most cases. In hashing more, a number of keys may be specified
       which are then hashed and the output used as class ID.  This ID
       is not deducible in beforehand, and may even change over time for
       a given flow if a perturb interval has been given.

       The range of class IDs can be limited by the divisor option,
       which is used for a modulus.

       src, dst
              Use source or destination address as key. In case of IPv4
              and TIPC, this is the actual address value. For IPv6, the
              128bit address is folded into a 32bit value by XOR'ing the
              four 32bit words. In all other cases, the kernel-internal
              socket address is used (after folding into 32bits on 64bit

       proto  Use the layer four protocol number as key.

              Use the layer four source port as key. If not available,
              the kernel-internal socket address is used instead.

              Use the layer four destination port as key. If not
              available, the associated kernel-internal dst_entry
              address is used after XOR'ing with the packet's layer
              three protocol number.

       iif    Use the incoming interface index as key.

              Use the packet's priority as key. Usually this is the IP
              header's DSCP/ECN value.

       mark   Use the netfilter fwmark as key.

       nfct   Use the associated conntrack entry address as key.

       nfct-src, nfct-dst, nfct-proto-src, nfct-proto-dst
              These are conntrack-aware variants of src, dst, proto-src
              and proto-dst.  In case of NAT, these are basically the
              packet header's values before NAT was applied.

              Use the packet's destination routing table entry's realm
              as key.

       sk-gid For locally generated packets, use the user or group ID
              the originating socket belongs to as key.

              Use the packet's vlan ID as key.

       rxhash Use the flow hash as key.

EXAMPLES         top

       Classic SFQ hash:

              tc filter add ... flow hash \
                   keys src,dst,proto,proto-src,proto-dst divisor 1024

       Classic SFQ hash, but using information from conntrack to work
       properly in combination with NAT:

              tc filter add ... flow hash \
                   keys nfct-src,nfct-dst,proto,nfct-proto-src,nfct-proto-dst \
                   divisor 1024

       Map destination IPs of to classids 1-256:

              tc filter add ... flow map \
                   key dst addend - divisor 256

       Alternative to the above:

              tc filter add ... flow map \
                   key dst and 0xff

       The same, but in reverse order:

              tc filter add ... flow map \
                   key dst and 0xff xor 0xff

SEE ALSO         top

       tc(8), tc-ematch(8), tc-sfq(8)

COLOPHON         top

       This page is part of the iproute2 (utilities for controlling
       TCP/IP networking and traffic) project.  Information about the
       project can be found at 
       If you have a bug report for this manual page, send it to,  This page was
       obtained from the project's upstream Git repository
       ⟨⟩ on
       2023-12-22.  (At that time, the date of the most recent commit
       that was found in the repository was 2023-12-20.)  If you
       discover any rendering problems in this HTML version of the page,
       or you believe there is a better or more up-to-date source for
       the page, or you have corrections or improvements to the
       information in this COLOPHON (which is not part of the original
       manual page), send a mail to

iproute2                       20 Oct 2015          Flow filter in tc(8)

Pages that refer to this page: tc(8)tc-flower(8)