network connection to proxmox server cuts out when enabling bridge in vm?

[0nobody0]

hello,

i'm working on setting up a network bridge in a proxmox VM running rocky 9.5. a test bridge br0 created with iproute2 works fine. when i try to create a similar persistent bridge using nmcli per https://docs.redhat.com/en/document...e-by-using-nmcli_configuring-a-network-bridge the wired link for the proxmox server cuts out completely - the link lights on the back of the NIC immediately turn off.

logging in locally as root to the promox server, stopping the VM (qm stop <VM id>), then re-enabling the host NIC and bridge (ip link set <interface> down/up) appears to do nothing. same wth dis/re-connecting the network cable. i haven't isolated it yet, but the connection comes back up at some point after rebooting the server / dis/re-connecting the network cable / or a timeout expires?

unfortunately i don't have access to the router/switches for this network.

the proxmox install (8.3.0) has been running smoothly for a while. the rocky 9.5 VM network setup is:

guest VM nic ens18 -> proxmox vmbr0 -> hypervisor nic ensp0s31f6 -> lan/wan
guest VM nic ens19 -> proxmox vmbr1 -> not bridged to hypervisor NIC, used for an isolated network with other VMs

here's what works to set up the iproute2 bridge:

ip link add name br0 type bridge
ip link set dev br0 up
ip addr add 10.x.x.20/16 dev br0
ip route append default via 10.x.x.1 dev br0
ip link set ens18 master br0
ip addr del 10.x.x.20/16 dev ens18

here's the commands for the nmcli bridge causing issues:

nmcli conn del ens18
nmcli conn add type bridge con-name br0 ifname br0
nmcli conn add type ethernet port-type bridge con-name br0-port1 ifname ens18 controller br0 # connection cuts out here for proxmox server

if i don't delete the ens18 connection i can set network details for br0, but then the same cut-off happens bringing up the bridge, and resetting ens18 later on:

nmcli conn modify br0 ipv4.addresses '10.x.x.20/16' ipv4.gateway '10.x.x.1' ipv4.dns '10.x.x.1' ipv4.method manual ipv6.method disabled
nmcli conn up br0
nmcli conn down ens18
nmcli conn up ens18

any help is greatly appreciated

 

[0nobody0]

to follow up: this issue just came up again outside of the virtual environment and it turned out to be bpdu guard shutting down the port on the switch.