Thanks, Mike. When running tcpdump on the VM I'm not seeing traffic unless it's explicitly intended for that particular VM, so no traffic between the other VMs is getting forwarded from the virtual interface to the "network appliance" VM. There is connectivity between the VMs on the private network and the "network appliance" VM which is acting as a gateway. Here's the output of the brctl command: virbr1 bridge id 8000.5254007e2f5b designated root 8000.5254007e2f5b root port 0 path cost 0 max age 19.99 bridge max age 19.99 hello time 1.99 bridge hello time 1.99 forward delay 0.00 bridge forward delay 0.00 ageing time 299.95 hello timer 0.29 tcn timer 0.00 topology change timer 0.00 gc timer 0.29 hash elasticity 4 hash max 512 mc last member count 2 mc init query count 2 mc router 1 mc snooping 1 mc last member timer 0.99 mc membership timer 259.96 mc querier timer 254.96 mc query interval 124.98 mc response interval 9.99 mc init query interval 31.24 flags virbr1-nic (0) port id 0000 state disabled designated root 8000.5254007e2f5b path cost 100 designated bridge 8000.5254007e2f5b message age timer 0.00 designated port 8001 forward delay timer 0.00 designated cost 0 hold timer 0.00 mc router 1 flags I'm not sure why virbr1-nic is showing up as disabled, and also why the vnet# interfaces don't show up (they do show up on another host, although VMs on that host are having the same non-promiscuous issue as these VMs). I've tried this with and without NAT, as well as with STP on/off with no effect. Thanks, Kevin