NAME

       police - policing action

SYNOPSIS

       tc  ...  action  police  rate RATE burst BYTES[/BYTES] [ mtu BYTES[/BYTES] ] [ peakrate RATE ] [ overhead
               BYTES ] [ linklayer TYPE ] [ CONTROL ]

       tc ... filter ... [ estimator SAMPLE AVERAGE ] action police avrate RATE [ CONTROL ]

       CONTROL := conform-exceed EXCEEDACT[/NOTEXCEEDACT

       EXCEEDACT/NOTEXCEEDACT := { pipe | ok | reclassify | drop | continue | goto chain CHAIN_INDEX }

DESCRIPTION

       The police action allows to limit bandwidth of traffic matched by the filter it is attached to. Basically
       there  are  two different algorithms available to measure the packet rate: The first one uses an internal
       dual token bucket and is configured  using  the  rate,  burst,  mtu,  peakrate,  overhead  and  linklayer
       parameters. The second one uses an in-kernel sampling mechanism. It can be fine-tuned using the estimator
       filter parameter.

OPTIONS

       rate RATE
              The maximum traffic rate of packets passing this action. Those exceeding it  will  be  treated  as
              defined by the conform-exceed option.

       burst BYTES[/BYTES]
              Set  the  maximum  allowed burst in bytes, optionally followed by a slash ('/') sign and cell size
              which must be a power of 2.

       mtu BYTES[/BYTES]
              This is the maximum packet size handled by the policer (larger ones  will  be  handled  like  they
              exceeded  the  configured  rate).  Setting  this  value  correctly  will  improve  the scheduler's
              precision.  Value formatting is identical to burst above. Defaults to unlimited.

       peakrate RATE
              Set the maximum bucket depletion rate, exceeding rate.

       avrate RATE
              Make use of an in-kernel bandwidth rate estimator and match the given RATE against it.

       overhead BYTES
              Account for protocol overhead of encapsulating output devices when computing rate and peakrate.

       linklayer TYPE
              Specify the link layer type.  TYPE may be one of ethernet (the default), atm or  adsl  (which  are
              synonyms).  It  is  used  to  align the precomputed rate tables to ATM cell sizes, for ethernet no
              action is taken.

       estimator SAMPLE AVERAGE
              Fine-tune the in-kernel packet rate estimator.  SAMPLE and AVERAGE are time values and control the
              frequency in which samples are taken and over what timespan an average is built.

       conform-exceed EXCEEDACT[/NOTEXCEEDACT]
              Define  how  to  handle  packets  which exceed or conform the configured bandwidth limit. Possible
              values are:

              continue
                     Don't do anything, just continue with the next action in line.

              drop   Drop the packet immediately.

              shot   This is a synonym to drop.

              ok     Accept the packet. This is the default for conforming packets.

              pass   This is a synonym to ok.

              reclassify
                     Treat the packet as non-matching to the filter this action is attached to and continue with
                     the next filter in line (if any). This is the default for exceeding packets.

              pipe   Pass the packet to the next action in line.

EXAMPLES

       A  typical  application  of  the  police  action is to enforce ingress traffic rate by dropping exceeding
       packets. Although better done on the sender's side, especially in scenarios with  lack  of  peer  control
       (e.g. with dial-up providers) this is often the best one can do in order to keep latencies low under high
       load. The following establishes input bandwidth policing to 1mbit/s  using  the  ingress  qdisc  and  u32
       filter:

              # tc qdisc add dev eth0 handle ffff: ingress
              # tc filter add dev eth0 parent ffff: u32 \
                   match u32 0 0 \
                   police rate 1mbit burst 100k

       As an action can not live on it's own, there always has to be a filter involved as link between qdisc and
       action. The example above uses u32 for that, which is configured to effectively match any packet (passing
       it to the police action thereby).

SEE ALSO

       tc(8)