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

       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 parameter.

       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

              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 systems).

       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

       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 prop‐
       erly 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
       netdev@vger.kernel.org, shemminger@osdl.org.  This page was obtained
       from the project's upstream Git repository
       ⟨https://git.kernel.org/pub/scm/network/iproute2/iproute2.git⟩ on
       2020-08-13.  (At that time, the date of the most recent commit that
       was found in the repository was 2020-06-24.)  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)