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 specific 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)