179 lines
5.4 KiB
Groff
179 lines
5.4 KiB
Groff
.\"
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.\" $FreeBSD$
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.\"
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.Dd September 28, 1998
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.Dt DUMMYNET 4
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.Os
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.Sh NAME
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.Nm dummynet
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.Nd Flexible bandwidth manager and delay emulator
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.Sh SYNOPSIS
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.Fd #include <sys/types.h>
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.Fd #include <sys/queue.h>
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.Fd #include <netinet/in.h>
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.Fd #include <netinet/ip_fw.h>
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.Ft int
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.Fn setsockopt raw_socket IPPROTO_IP "ipfw option" "struct ipfw" size
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.Sh DESCRIPTION
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dummynet is a system facility that permits the control of traffic
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going through the various network interfaces, by applying bandwidth
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and queue size limitations, and simulating delays and losses.
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.Pp
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In its current implementation,
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packet selection is done with the
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.Nm ipfw
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program, by means of
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.Dq pipe
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rules.
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A dummynet
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.Em pipe
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is characterized by a bandwidth, delay, queue size, and loss
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rate, which can be configured with the
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.Nm ipfw
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program.
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Pipes are
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numbered from 1 to 65534, and packets can be passed through multiple
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pipes depending on the ipfw configuration.
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.Pp
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Dummynet operates at the ip level, but if bridging extensions are
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enabled, it is possible to pass bridged packets through pipes as well.
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.Sh USAGE
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Packets are sent to a pipe using the command
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.Bd -literal
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ipfw add pipe NNN ....
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.Ed
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.Pp
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and pipes are configured as follows:
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.Bd -literal
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ipfw pipe NNN config bw B delay D queue Q plr P
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.Ed
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.Pp
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where the bandwidth B can be expressed in bit/s, Kbit/s, Mbit/s,
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Bytes/s, KBytes/s, MBytes/s , delay in milliseconds, queue size in
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packets or Bytes, plr is the fraction of packets randomly dropped.
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.Pp
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Getting ipfw to work right is not very intuitive, especially when
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the system is acting as a router or a bridge.
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.Pp
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When acting as a router, the same ruleset is applied on both the
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input and the output path for routed packets, so you have to make
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sure that a packet does not go through the same pipe twice (unless
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this is what you really want).
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.Pp
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When acting as a bridge, the
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.Nm ipfw
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filter is invoked only once, in the input path,
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for bridged packets.
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.Pp
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Also, when simulating true full-duplex channels, be sure to pass
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traffic through two different pipes, depending on the direction.
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E.g. a suitable rule set for simulating an asymmetric bidirectional
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link would be the following:
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.Bd -literal
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ipfw add pipe 1 ip from A to B out
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ipfw add pipe 2 ip from B to A in
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ipfw pipe 1 config bw 1Mbit/s delay 80ms
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ipfw pipe 2 config bw 128Kbit/s delay 300ms
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.Ed
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.Sh OPERATION
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The
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.Nm ipfw
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code is used to select packets that must be subject to
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bandwidth/queue/delay/losses, and returns the identifier of
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the ``pipe'' describing such limitations.
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.Pp
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Selected packets are first queued in a bounded size queue, from which
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they are extracted at the programmed rate and passed to a second queue
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where delay is simulated.
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At the output from the second queue packets
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are reinjected into the protocol stack at the same point they came
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from (i.e. ip_input(), ip_output(), bdg_forward() ).
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Depending on the setting of the sysctl variable
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.Ql net.inet.ip.fw.one_pass ,
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packets coming from a pipe can be either forwarded to their
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destination, or passed again through the
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.Nm ipfw
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rules, starting from the one after the matching rule.
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.Pp
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.Nm
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performs its task once per timer tick.
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The granularity of operation is
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thus controlled by the kernel option
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.Bd -literal
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options HZ
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.Ed
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.Pp
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whose default value (100) means a granularity of 10ms.
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For an accurate simulation of high data rates it might be necessary to
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reduce the timer granularity to 1ms or less.
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Consider, however,
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that some interfaces using programmed I/O may require a considerable
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time to output packets.
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So, reducing the granularity too much might
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actually cause ticks to be missed thus reducing the accuracy of
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operation.
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.Sh KERNEL OPTIONS
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The following options in the kernel configuration file are related
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to
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.Nm
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operation:
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.Bd -literal
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IPFIREWALL - enable ipfirewall (required for dummynet).
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IPFIREWALL_VERBOSE - enable firewall output.
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IPFIREWALL_VERBOSE_LIMIT - limit firewall output.
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DUMMYNET - enable dummynet operation.
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NMBCLUSTER - set the amount of network packet buffers
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HZ - sets the timer granularity
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.Ed
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.Pp
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Generally, the following options are required:
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.Bd -literal
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options IPFIREWALL
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options DUMMYNET
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.Ed
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.Pp
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additionally, one may want to increase the number
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of mbuf clusters (used to store network packets) according to the
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sum of the bandwidth-delay products and queue sizes of all configured
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pipes.
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.Sh SYSCTL VARIABLES
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.Pp
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.Ql net.inet.ip.fw.one_pass
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is set to 1 if we want packets to pass through the firewall code only
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once.
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.Pp
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.Ql net.link.ether.bridge_ipfw
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is set if we want bridged packets to pass through the firewall code.
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.Sh COMMANDS
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The following socket options are used to manage pipes:
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.Pp
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IP_DUMMYNET_CONFIGURE updates a pipe configuration (or creates a
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new one.
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.Pp
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IP_DUMMYNET_DEL deletes all pipes having the matching rule number.
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.Pp
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IP_DUMMYNET_GET returns the pipes matching the number.
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.Pp
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IP_FW_FLUSH flushes the pipes matching the number.
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.Pp
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When the kernel security level is greater than 2, only IP_DUMMYNET_GET
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is allowed.
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.Sh SEE ALSO
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.Xr setsockopt 2 ,
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.Xr ip 4 ,
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.Xr ipfw 8 ,
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.Xr sysctl 8
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.Sh BUGS
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This manpage is not illustrating all the possible ways to use
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dummynet.
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.Sh HISTORY
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.Nm
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was initially implemented as a testing tool for TCP congestion control
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by
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.An Luigi Rizzo Aq luigi@iet.unipi.it ,
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as described on ACM Computer
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Communication Review, Jan.97 issue.
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Later it has been then modified
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to work at the ip and bridging level, and integrated with the IPFW
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packet filter.
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