Networking

This article covers how to create additional network bridges and set up an isolated network for your virtual machines — separating VM traffic from the Proxmox management interface.
After installation, Proxmox creates one Linux bridge:
vmbr0 — connected to your physical NIC (eth0/enp3s0), carries management and VM traffic
 
Creating a New Bridge for VM Traffic
 
In the web console, go to your Node > Network
Click Create > Linux Bridge
Configure:
    • Name: vmbr1 (or any available name)
    • IP Address / CIDR: leave blank for a pure internal bridge (no host routing), OR assign an IP if you want the host to route between networks
    • Bridge ports: leave blank for internal-only, or enter a NIC name to connect to physical network
Click Create, then click Apply Configuration
Reboot may be needed for changes to take full effect
 
Assigning a VM to a New Bridge
 
Select the VM > Hardware > Select the network device
Click Edit, change the Bridge to vmbr1
Click OK
Reboot the VM
 
NAT and Routing
This step is Optional. To allow VMs on an internal bridge (vmbr1) to reach the internet through the Proxmox host, enable IP forwarding and NAT:
Enable IP forwarding:
echo 'net.ipv4.ip_forward=1' >> /etc/sysctl.conf
sysctl -p
Add NAT rule (replace 192.168.100.0/24 with your VM subnet):
iptables -t nat -A POSTROUTING -s 192.168.100.0/24 -o vmbr0 -j MASQUERADE
Make the rule persistent (install iptables-persistent):
apt install -y iptables-persistent