---
name: "dummynet"
section: "4"
platform: "linux"
package: "freebsd-manpages"
version: "6.0-5"
release: "Debian 4.0 (Etch)"
platforms: ["linux", "freebsd", "macos"]
url: "https://new.carta.tech/dummynet"
---

# dummynet(4)

traffic shaper, bandwidth manager and delay emulator

## NAME

**dummynet** – traffic shaper, bandwidth manager and delay emulator

## DESCRIPTION

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)](/ipfw/8.md) utility, so please refer to the [ipfw(8)](/ipfw/8.md) 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

- NMBCLUSTERS

  set the amount of network packet buffers

- 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.

## SEE ALSO

[setsockopt(2)](/setsockopt/2.md), [bridge(4)](/bridge/4.md), [if\_bridge(4)](/if_bridge/4.md), [ip(4)](/ip/4.md), [ipfw(8)](/ipfw/8.md), [sysctl(8)](/sysctl/8.md)

## HISTORY

The **dummynet** facility 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 modified to work at the IP and bridging levels, integrated with the [ipfw(4)](/ipfw/4.md) packet filter, and extended to support multiple queueing and scheduling policies.