Each bridge that you create by using the dladm create-bridge command is represented as an identically named Service Management Facility (SMF) instance of svc:/network/bridge. Each instance runs a copy of the /usr/lib/bridged daemon, which implements the STP.
For example, the following command creates a bridge called pontevecchio:
# dladm create-bridge pontevecchio
The system creates an SMF service instance called svc:/network/bridge:pontevecchio and an observability node called /dev/net/pontevecchio0. The observability node is intended for use with the snoop command and the wireshark packet analyzer. You can use the dlstat command to obtain the run time statistics of the bridge.
For safety purposes, all ports run standard STP by default. A bridge that does not run some form of bridging protocol, such as STP, can form long-lasting forwarding loops in the network. Because Ethernet has no hop-count or time-to-live (TTL) on packets, any such loops are fatal to the network.
When a particular port is not connected to another bridge (for example, because the port has a direct point-to-point connection to a host system), you can administratively disable STP for that port. Even if all ports on a bridge have STP disabled, the STP daemon still runs for the following reasons:
To handle any new ports that are added
To implement BPDU guarding
To enable or disable forwarding on the ports, as necessary
When a port has STP disabled, the bridged daemon continues to listen for BPDUs (BPDU guarding). The daemon uses syslog to flag any errors and disables forwarding on the port to indicate a serious network misconfiguration. The link is re-enabled when the link goes down and comes up again, or when you manually remove the link and add it again.
If you disable the SMF service instance for a bridge, the bridge stops on those ports as the STP daemon is stopped. If the instance is restarted, STP starts from its initial state.