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     dummynet — traffic shaper, bandwidth manager and delay emulator


     The dummynet system facility permits the control of traffic going through
     the various network interfaces, by applying bandwidth and queue size
     limitations, implementing different scheduling and queue management
     policies, and emulating delays and losses.

     The user interface for dummynet is implemented by the ipfw(8) utility, so
     please refer to the ipfw(8) manpage for a complete description of the
     dummynet capabilities and how to use it.

   Kernel Options
     The following options in the kernel configuration file are related to
     dummynet operation:

           IPFIREWALL                enable ipfirewall (required for dummynet)
           IPFIREWALL_VERBOSE        enable firewall output
           IPFIREWALL_VERBOSE_LIMIT  limit firewall output
           DUMMYNET                  enable dummynet operation
           HZ                        set the timer granularity

     Generally, the following options are required:

           options IPFIREWALL
           options DUMMYNET
           options HZ=1000         # strongly recommended

     Additionally, one may want to increase the number of mbuf clusters (used
     to store network packets) according to the sum of the bandwidth-delay
     products and queue sizes of all configured pipes.


     setsockopt(2), if_bridge(4), ip(4), ipfw(8), sysctl(8)


     The dummynet facility was initially implemented as a testing tool for TCP
     congestion control by Luigi Rizzo ⟨⟩, as described on
     ACM Computer Communication Review, Jan.97 issue.  Later it has been
     modified to work at the IP and bridging levels, integrated with the
     ipfw(4) packet filter, and extended to support multiple queueing and
     scheduling policies.