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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

   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