tc-flow(8) - phpMan

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 ] [ 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. 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 divi-
sor 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 de-
tailed 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 ac-
tual 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 ad-
dress 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 ker-
nel-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 be-
longs 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