Flow filter in tc(8)      (20 Oct 2015)      Flow filter in tc(8)

          flow - flow based traffic control filter

          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 | NUM

          ID := X:Y

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

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

          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.

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          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

               or NUM
                   Perform bitwise OR operation with numeric value

               xor NUM
                   Perform bitwise XOR operation with numeric value

               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 operations, NUM is assumed to
               be an unsigned, 32bit integer value. For the addend
               operation, NUM may be much more complex: It may be pre-
               fixed by a minus ('-') sign to cause subtraction
               instead of addition and for keys of src, dst, nfct-src
               and 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.

          In mapping mode, a single key is used (after optional permu-
          tation) 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

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     Flow filter in tc(8)      (20 Oct 2015)      Flow filter in tc(8)

          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 fold-
               ing into 32bits on 64bit systems).

               Use the layer four protocol number as key.

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

               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,
               These are conntrack-aware variants of src, dst, proto-
               src and 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.

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               Use the flow hash as key.

          Classic SFQ hash:

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

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

               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

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

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