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