Flow filter in tc(8) Linux Flow filter in tc(8)
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 ] [ ac-
tion 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. X must match
qdisc's/class's major handle (if omitted, the correct value is
chosen automatically). If the whole baseclass is omitted, Y de-
faults 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 us-
ing 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 hash-
ing 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 ad-
dress 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 1-256:
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)
iproute2 20 Oct 2015 Flow filter in tc(8)
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