KVM Switch Network Configuration

KVM network configuration involves setting up virtual NICs, choosing between NAT or bridged networking, and optionally using PCIe passthrough for high-performance connectivity.

Virtual Network Setup in KVM

Networking in a KVM environment is achieved by creating virtual Network Interface Cards (vNICs) for each guest VM. These vNICs can be connected in several ways:

• Default NAT Network: Uses libvirt's virtual network with NAT to allow guests outbound internet access without complex host configuration. This is ideal for development or testing environments .
• Bridged Network: Maps a vNIC to a physical host interface, making the VM appear as a separate host on the same subnet. This is suitable when VMs need to be accessible from other devices on the network .
• Direct Host Interface: Uses the host's physical interface directly, often via the macvtap driver, providing performance similar to bridged networking but easier to maintain .
• PCIe Passthrough: Allocates a physical PCIe network device to a VM, either exclusively (direct) or shared via SR-IOV, for high-performance networking .

Tools for Configuration

• virsh: Command-line tool to manage virtual networks. Commands include virsh net-list --all to list networks and virsh net-info <network> to view details .
• nmcli: NetworkManager CLI for creating Linux bridges and assigning IP addresses. Example: create a bridge br0, add a slave interface, and configure autoconnect and IP settings .
• brctl/ip link: Legacy or alternative method to create and manage Linux bridges for KVM networking .

Example: Bridged Network Configuration

1. Create a bridge interface: nmcli connection add type bridge con-name br0 ifname br0
2. Add a physical interface as a slave: nmcli connection add type bridge-slave ifname ens3 master br0
3. Assign IP and gateway: nmcli connection modify br0 ipv4.addresses 192.168.10.1/24 ipv4.method manual
4. Activate the bridge: nmcli connection up br0 This allows the VM to communicate directly with other devices on the same network.

KVM Switch Integration

For physical KVM switches controlling multiple computers:

• Connect each computer's video output and USB ports to the KVM switch .
• Ensure the switch supports the port types (HDMI, DisplayPort, USB) and resolution requirements.
• Network configuration on each host can remain independent, but bridged or NAT networking in KVM ensures VMs maintain connectivity even when switching between hosts .

Best Practices

• Use NAT for simple setups or testing environments.
• Use bridged networking when VMs need to be accessible externally.
• Consider PCIe passthrough for high-performance or low-latency network requirements.
• Always verify IP assignments and routing to avoid conflicts.
• Use management tools like Oracle Linux Virtualization Manager for complex network topologies . By combining virtual network configuration with proper KVM switch setup, you can efficiently manage multiple VMs and hosts while maintaining reliable network connectivity.