Netgear XCM8806 Chassis User Manual - Page 523

NETGEAR 8800 User Manual • The port sends BPDUs • When configured for MSTP, the port runs a partial state machine • If BPDUs are received, the port enters the blocking state • If subsequent BPDUs are not received, the port attempts to enter the forwarding state • Edge port running 802.1D-2004 with safeguard enabled: • The port sends BPDUs • The port runs a state machine • If BPDUs are received, the port behaves as a normal RSTP port by entering the forwarding state and participating in RSTP • If subsequent BPDUs are not received, the port attempts to become the edge port again Edge port with safeguard prevents accidental or deliberate misconfigurations (loops) by having edge ports enter the blocking state upon receiving a BPDU. The 802.1D-2004 standard implements a bridge detection mechanism that causes an edge port to transition to a non-edge port upon receiving a BPDU; however, if the former edge port does not receive any subsequent BPDUs during a pre-determined interval, the port attempts to become an edge port. If an 802.1D-2004 compliant safeguard port (edge port) connects to an 802.1D-1998 compliant edge port with safeguard configured, the old safeguard port enters the blocking state. Although the new safeguard port becomes a designated port, the link is not complete (and thus no loop is formed) because one side of the link is blocked. Restricted Role In a large metro environment, to prevent external bridges from influencing the spanning tree active topology, the following commands have been introduced for Rapid Spanning Tree Protocol (RSTP) and Multiple Spanning Tree Protocol (MSTP). • configure stpd ports restricted-role enable • This command enables restricted role on a specified port in the core network to prevent external bridges from influencing the spanning tree active topology. • Restricted role should not be enabled with edge mode. • stpd_name-Specifies an STPD name on the switch. • port_list-Specifies one or more ports or slots and ports. • Enabling restricted role causes a port to not be selected as a root port, even if it has the best spanning tree priority vector. Such a port is selected as an alternate port after the root port is selected. The restricted role is disabled by default. If set, it can cause a lack of spanning tree connectivity. • A network administrator enables restricted role to prevent external bridges from influencing the spanning tree active topology. • configure stpd ports restricted-role disable • This command disables restricted role on a specified port in the core network. • stpd_name-Specifies an STPD name on the switch. Chapter 18. STP | 523