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

       sample - packet sampling tc action

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

       tc ... action sample index INDEX

       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.

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

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

              The output interface index of the packet. This field is not rel-
              evant on ingress sampling

              The size of the original packet (before truncation)

              The psample group the packet was sent to

              A  sequence  number of the sampled packet. This number is incre-
              mented with each sampled packet of the current psample group

              The rate the packet was sampled with

       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

       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.

       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

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

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