NAME

       flow - flow based traffic control filter

SYNOPSIS

       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

       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

       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. If X is omitted, it is assumed to be zero.

       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 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

       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.

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

       proto-dst
              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.

       priority
              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.

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

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

       vlan-tag
              Use the packet's vlan ID as key.

       rxhash Use the flow hash as key.

EXAMPLES

       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 192.168.0.0/24 to classids 1-257:

              tc filter add ... flow map \
                   key dst addend -192.168.0.0 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

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