centos man page for sample

Packet sample action in tc(8)					       Linux					     Packet sample action in tc(8)

NAME
       sample - packet sampling tc action

SYNOPSIS
       tc ... action sample rate RATE group GROUP [ trunc SIZE ] [ index INDEX ]

       tc ... action sample index INDEX

DESCRIPTION
       The sample action allows sampling packets matching classifier.

       The  packets  are  chosen randomly according to the rate parameter, and are sampled using the psample generic netlink channel. The user can
       also specify packet truncation to save user-kernel traffic. Each sample includes some informative metadata about the original packet, which
       is sent using netlink attributes, alongside the original packet data.

       The  user  can either specify the sample action parameters as presented in the first form above, or use an existing sample action using its
       index, as presented in the second form.

SAMPLED PACKETS METADATA FIELDS
       The metadata are delivered to userspace applications using the psample generic netlink channel, where each sample  includes  the  following
       netlink attributes:

       PSAMPLE_ATTR_IIFINDEX
	      The input interface index of the packet, if there is one.

       PSAMPLE_ATTR_OIFINDEX
	      The output interface index of the packet. This field is not relevant on ingress sampling

       PSAMPLE_ATTR_ORIGSIZE
	      The size of the original packet (before truncation)

       PSAMPLE_ATTR_SAMPLE_GROUP
	      The psample group the packet was sent to

       PSAMPLE_ATTR_GROUP_SEQ
	      A sequence number of the sampled packet. This number is incremented with each sampled packet of the current psample group

       PSAMPLE_ATTR_SAMPLE_RATE
	      The rate the packet was sampled with

OPTIONS
       rate RATE
	      The packet sample rate.  RATE is the expected ratio between observed packets and sampled packets. For example, RATE of 100 will lead
	      to an average of one sampled packet out of every 100 observed.

       trunc SIZE
	      Upon set, defines the maximum size of the sampled packets, and causes truncation if needed

       group GROUP
	      The psample group the packet will be sent to. The psample module defines the concept of groups, which allows the user to match  spe-
	      cific sampled packets in the case of multiple sampling rules, thus identify only the packets that came from a specific rule.

       index INDEX
	      Is  a  unique  ID  for  an  action. When creating new action instance, this parameter allows to set the new action index. When using
	      existing action, this parameter allows to specify the existing action index.  The index must 32bit  unsigned  integer  greater  than
	      zero.

EXAMPLES
       Sample one of every 100 packets flowing into interface eth0 to psample group 12:

	      tc qdisc add dev eth0 handle ffff: ingress
	      tc filter add dev eth0 parent ffff: matchall 
		   action sample rate 100 group 12 index 19

       Use the same action instance to sample eth1 too:

	      tc qdisc add dev eth1 handle ffff: ingress
	      tc filter add dev eth1 parent ffff: matchall 
		   action sample index 19

SEE ALSO
       tc(8), tc-matchall(8) psample(1)

iproute2							    31 Jan 2017 				     Packet sample action in tc(8)