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)