Spanning tree loop guard
DC CAFCFirst Claim
1. In an intermediate network device having a plurality of ports for forwarding network messages within a bridged network, a method for preventing the formation of loops within the bridged network, the method comprising the steps of:
- executing a spanning tree protocol (STP) at the intermediate network device so as to elect a root of the bridged network and to transition at least one of the device'"'"'s ports among a plurality of spanning tree port states, including a discarding state, a listening state and a forwarding state;
periodically receiving configuration bridge protocol data unit (BPDU) messages at one or more of the device'"'"'s ports;
in response to the periodic receipt of BPDU messages being stopped on a given port, (1) preventing the given port from transitioning to the forwarding spanning tree port state, if the given port is in a spanning tree port state other than the forwarding spanning tree port state, or (2) precluding the given port from forwarding or receiving network messages, if the given port is in the forwarding spanning tree port state.
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Abstract
A system and method prevents the formation of loops that are not detected by the Spanning Tree Protocol (STP). An intermediate network device preferably includes a plurality of ports for receiving and forwarding network messages and a STP engine in communicating relationship with the ports. The STP engine transitions the ports among a plurality of spanning tree port states, including a discarding state, a learning state and a forwarding state. The device further includes a loop guard engine that is in communicating relationship with the STP engine and the ports. The loop guard engine monitors the receipt of configuration bridge protocol data unit (BPDU) messages by the ports. If a given port stops receiving BPDU messages, the loop guard engine prevents the STP engine from transitioning the given port to the forwarding state. Instead, the loop guard engine preferably causes the port to transition to a new state in which networks messages are explicitly blocked from being forwarded or received. If the given port subsequently receives a BPDU message, the loop guard engine releases the port from the new state, thereby allowing it to transition to some other spanning tree port state.
109 Citations
15 Claims
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1. In an intermediate network device having a plurality of ports for forwarding network messages within a bridged network, a method for preventing the formation of loops within the bridged network, the method comprising the steps of:
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executing a spanning tree protocol (STP) at the intermediate network device so as to elect a root of the bridged network and to transition at least one of the device'"'"'s ports among a plurality of spanning tree port states, including a discarding state, a listening state and a forwarding state; periodically receiving configuration bridge protocol data unit (BPDU) messages at one or more of the device'"'"'s ports; in response to the periodic receipt of BPDU messages being stopped on a given port, (1) preventing the given port from transitioning to the forwarding spanning tree port state, if the given port is in a spanning tree port state other than the forwarding spanning tree port state, or (2) precluding the given port from forwarding or receiving network messages, if the given port is in the forwarding spanning tree port state. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. An intermediate network device configured to receive and forward network messages within a bridged network, the device having a plurality of ports for connecting the device to one or more network entities or other devices, the intermediate network device comprising:
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a spanning tree protocol (STP) engine configured and arranged to elect a root of the bridged network and to transition at least some of the device'"'"'s ports among a plurality of spanning tree port states, including a discarding or blocking state, a listening state and a forwarding state; and a loop guard engine cooperating with the STP engine, wherein configuration bridge protocol data unit (BPDU) messages are periodically received at one or more of the device'"'"'s ports, and in response to the periodic receipt of BPDU messages being stopped on a given port, the loop guard engine (1) prevents the given port from transitioning to the forwarding spanning tree port state, if the given port is in a spanning tree port state other than the forwarding spanning tree port state, or (2) precludes the given port from forwarding or receiving network messages. - View Dependent Claims (11, 12, 13, 14, 15)
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Specification