Limiting Bandwidth For Network testing ISDN Simulator

IP_DUMMYNET

This is something I needed two years ago. I wanted to simulate a fixed datapipe for ISDN testing, without the overhead / cost of tying up two ISDN lines. This would have been ideal. Still could use something like this so here is the details:

dummynet is a flexible tool originally designed for testing networking protocols, and since then (mis)used for bandwidth management.

It simulates/enforces queue and bandwidth limitations, delays, packet losses, and multipath effects. It also implements a variant of Weighted Fair Queueing called WF2Q+. It can be used on user's workstations, or on FreeBSD machines acting as routers or bridges.

Just to get the idea of what you can do with dummynet, e.g. by using dummynet on your workstation, or putting a PC with two ethernet cards between your network and your router and booting from the floppy-image below, here are a few examples :

These rules limit the total ICMP traffic (inbound+outbound) to 50Kbit/s

ipfw add pipe 1 icmp from any to any
ipfw pipe 1 config bw 50Kbit/s queue 10

These rules limit inbound traffic to 300Kbit/s for each host on your network 10.1.2.0/24.

ipfw add pipe 2 ip from any to 10.1.2.0/24
ipfw pipe 2 config bw 300Kbit/s queue 20 mask dst-ip 0x000000ff
[...]
dummynet works by intercepting packets (selected by ipfw rules - ipfw is one of the FreeBSD firewalls) in their way through the protocol stack, and passing them through one or more objects called queues and pipes, which simulate the effects of bandwidth limitations, propagation delays, bounded-size queues, packet losses, multipath. Pipes are fixed-bandwidth channels. Queues represent instead queues of packets, associated with a weight, which share the bandwidth of the pipe they are connected to proportionally to their weight.