Using Dummynet to simulate WAN links (2/2)

Thought it might be a good idea to split these sections as you only install once (Sounds like a bad Bond movie) So this part I'll deal with the operation of Dummynet:

Dummynet is contolled by the IPFW command but first we have to configure both Ethernet interfaces and set them up for bridging.

Configure both interfaces with an IP address within the same subnet (Any will do) as below:

# Ifconfig dc0 inet 192.168.0.253 netmask 255.255.255.0

# Ifconfig rl0 inet 192.168.0.252 netmask 255.255.255.0

Note: These IP address aren't actually visible to external devices, so they don't have to conform to the exiting subnet surrounding your server (It just appears as a L2 device, which the following command enables)

Then link both interfaces together so they will bridge packets rather than route them:

# sysctl –w net.link.ether.bridge.enable=1

# sysctl –w net.link.ether.bridge.config=dc0,rl0

Now we can define a firewall pipe where we can control the bandwidth and delay

# ipfw add pipe 1 ip from any to any

# ipfw pipe 1 config bw 3200Kbit/s queue 10 delay 150ms

Now check the firewall rulesets and delete any lines which have a lower value than the rules you just entered.

# ipfw show

# ipfw delete

Dummynet is now up and configured. You should be able to change bandwidth as per the ipfw pipe command shown above.

Surprisingly it's quite accurate, you can verify this yourself (always good practice) with some other tools (Future blog me thinks) and maybe an FTP server.

Using Dummynet to simulate WAN links (1/2)

OK my 1st Blog so I'll try to make it slightly interesting rather than my 1st forray into basic programming with "hello world" plastered across the screen.

There are a few network simulation tools out there, but most of these will require a six figure sum to work with. There are some good alternatives that are free. One of which is included within the Free BSD Kernel called DummyNet. If you want to simulate artificial delay, packet loss and bandwidth policing, grab yourself a spare server and follow the instructions below:

PART 1 of 2 (Installing FreeBSD and checking DummyNet options)

Dummynet is a capability that lives within the Free BSD Kernel.

Free BSD 6.2 was used in my tests and can be found at http://www.freebsd.org/where.html

After installing onto a new device with two PCI Ethernet cards the kernel was rebuilt. To see if the Kernel requires rebuilding check the file at: /usr/src/sys/i386/conf/GENERIC

See if the following options are included

OPTIONS BRIDGE

OPTIONS IPFIREWALL

OPTIONS IPFIREWALL_VERBOSE

OPTIONS IPFIREWALL_VERBOSE_LIMIT

OPTIONS DUMMYNET

OPTIONS HZ=1000

If they are not copy (cp) this file to a new file called MYKERNEL and add the above options

Change to the /usr/src directory

# cd /usr/src

Compile the kernel with

# make buildkernel KERNCONF=MYKERNEL

Install the ner kernel

# make installkernel KERNCONF=MYKERNEL

The new kernel will be copied to the /boot/kernel directory as /boot/kernel/kernel and the old kernel will be moved to /boot/kernel.old/kernel. Now, shutdown the system and reboot to use your new kernel.

Next Blog see how to apply and run.