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)