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NAME | SYNOPSIS | DESCRIPTION | OPTIONS | KEYS | EXAMPLES | SEE ALSO | COLOPHON |
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Flow filter in tc(8) Linux 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 | 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 }
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.
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.
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.
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.
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
tc(8), tc-ematch(8), tc-sfq(8)
This page is part of the iproute2 (utilities for controlling
TCP/IP networking and traffic) project. Information about the
project can be found at
⟨http://www.linuxfoundation.org/collaborate/workgroups/networking/iproute2⟩.
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
2025-08-11. (At that time, the date of the most recent commit
that was found in the repository was 2025-08-08.) 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 man-pages@man7.org
iproute2 20 Oct 2015 Flow filter in tc(8)
Pages that refer to this page: tc(8), tc-flower(8)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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