Bridge design and host uplinks

A Linux bridge is a layer-2 switch in the host. The host address belongs on the bridge, while the physical interface becomes a port of that bridge.

Inspect without changing

ip -br link
ip -br address
bridge link
bridge vlan show
nmcli -f NAME,TYPE,DEVICE,STATE connection show

Request path mental model

For a libvirt-managed guest interface, reason from the management layer toward the workload edge:

libvirt control plane
        |
        v
host bridge / uplink
        |
        v
guest network edge

The control plane defines and manages the guest interface relationship. The host bridge is the layer-2 switching handoff. The guest-facing interface is the workload edge of that path. Use the actual bridge name from the host when tracing a real system.

NetworkManager pattern

nmcli connection add type bridge ifname br0 con-name br0
nmcli connection add type ethernet ifname eno1 master br0 con-name br0-port-eno1

Move the host IP configuration to br0 before activating the new topology. Remote changes can sever management connectivity; use console access, a maintenance window, and an explicit rollback connection profile.

Guest attachment proof

virsh domiflist guest01
ip link show master br0
bridge fdb show br br0

Do not run host DHCP on a bridge when the upstream network already owns address assignment unless the segments are intentionally isolated.