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DUMMYNET(4)            FreeBSD Kernel Interfaces Manual            DUMMYNET(4)

     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 lim-
     itations, implementing different scheduling and queue management poli-
     cies, 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), bridge(4), 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 modi-
     fied to work at the IP and bridging levels, integrated with the ipfw(4)
     packet filter, and extended to support multiple queueing and scheduling

FreeBSD 6.2                    October 28, 2002                    FreeBSD 6.2


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