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OpenWRT VM to create a subnet for you VMs

This is a guide how to create a subnet for your VMs that passes through a OpenWRT VM. This is good if you are doing alot of networking in your VMs or if you want to have more control over your VM network.

This is all done on Linux using KVM/QEMU with virt-manager so i will be showing screenshots of it. What you need:

• working internet connecting.
• Machine with KVM supported and setup
• a Guest OS for testing

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step 1 - get openwrt

from https://downloads.openwrt.org/ get the latest combined image for x86_64
As of writing this its at https://downloads.openwrt.org/releases/24.10.1/targets/x86/64/
when youve downloaded it put it you "VM" folder or whatever and you will need to convert the image to a qcow2

gunzip openwrt-x86-64-generic-ext4-combined.img.gz
qemu-img convert -f raw -O qcow2 openwrt-*.img openwrt.qcow2

once unzipped and converted we need to create a VM.

virt-manager -> [edit] -> [connection details] -> [virtual network] -> [+]

When creating the virtual network we need to make it Isolated as this will be our LAN. We will use default as our WAN.
We create our wm using our previously made openwrt.qcow2. No installation or anything will be needed. Before we enter the VM we customize the config. We need to add 2 NICs. The WAN (default virtual network) and the LAN (our isolated virtual network)

With the 2 NICs added we start the OpenWRT VM.

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step 2 - configure openwrt and host panel

Once in the router we define network configs at /etc/config/network

The following config was made for the purpose of further tunneling hence the dns options which are marked as OPTIONAL We define the lan and wan networks and as you can see we assign lan to '192.168.1.1'

config device
    option name 'br-lan'
    option type 'bridge'
    list ports 'eth1'

config interface 'lan'
    option device 'br-lan'
    option proto 'static'
    option dhcp_option 'DNS ADDRESS' ## OPTIONAL
    option ipaddr '192.168.1.1'
    option netmask '255.255.255.0'
    option ipassign '60'

config interface 'wan'
    option peerdns '0' ## OPTIONAL
    option device 'eth0'
    option proto 'dhcp'

we can now rerout our hosts ips.

to change the routing address for virbr1 to allow host access to router panel and for the subnets functionallity and connection between other machienes we need to do this on the host. This is assuming the device virbr1 by default gets ip '192.168.100.1' ( Check with "ip addr" to see what virbr1's address is before )

sudo ip addr add 192.168.1.10/24 dev virbr1
sudo ip addr del 192.168.100.1/24 dev virbr1

Now you can check on the host by going to '192.168.1.1' in your browser. You will get the LUCI panel. Note, this is only the panels, your host is still connected to the so called "WAN".
But if you add a new virtual machine and add only the isolated network NIC then all traffic for that VM will go through the OpenWRT router.