trema.conf

vswitch('firewall') { datapath_id '0xabc' }

vhost('outside') { ip '192.168.0.1' }
vhost('inside') { ip '192.168.0.2' }
vhost('inspector') {
  ip '192.168.0.3'
  promisc true
}

link 'firewall', 'outside'
link 'firewall', 'inside'
link 'firewall', 'inspector'