US 7,480,258 B1 · Cross stack rapid transition protocol

Abstract

A cross stack rapid transition protocol is provided for permitting multiple network devices organized as a stack to rapidly transition their ports in response to network changes so as to minimize traffic flow disruptions while avoiding loops. Each switch in the stack has a stack port that connects the switch to another switch in the stack, and a plurality of ports for connecting the switch to other entities of the computer network. Each switch includes a Spanning Tree Protocol (STP) entity that transitions the ports of the switch among a plurality of states including a forwarding state and a blocking state. Each switch also tracks which other switches are members of the switch stack. The stack port of each switch is transitioned to the forwarding state, and a single switch having connectivity to a root is elected to be a Stack Root. One or more other switches may have Alternate Stack Root Ports, that provide alternate paths to the root. If the current Stack Root loses connectivity to the root, the switch whose Alternate Stack Root Port represents the next best path to the root issues one or more proposal messages to the other members of the switch stack. These other members respond with an Acknowledgement, and the former Stack Root transitions its port to the blocking state. Once the proposing switch receives an Acknowledgment from all other active members of the switch stack, it transitions its Alternate Stack Root Port to the forwarding state so that network messages can be forwarded to and from switch stack.

Claims15

Dependent claims

In a plurality of intermediate network devices having a plurality of ports for forwarding network messages within a bridged network having a root, the plurality of intermediate network devices organized as a stack, each intermediate network device having a stack port for use in communicating with the other network devices of the stack, a method for efficiently transitioning the ports among a plurality of spanning tree protocol (STP) states, the method comprising the steps of:

executing the STP at each intermediate network device of the stack so as to assign the stack port of each device to either a Root Port Role or a Designated Port Role, and to assign a non-stack port at a single device of the stack to the Root Port Role;
transitioning the ports assigned to the Root Port Role and the Designated Port Role to a forwarding STP state;
designating all non-stack ports at the devices of the stack that provide connectivity to the root, other than the non-stack port assigned to the Root Port Role, as Alternate Stack Root Ports;
transitioning the Alternate Stack Root Ports to a discarding STP state;
and
in response to a failure at the non-stack port assigned to the Root Port Role, transitioning a selected one of the Alternate Stack Root Ports from the discarding STP state directly to the forwarding STP state, without transitioning the selected port through any intermediary STP states, so that the selected Alternate Stack Root Port assumes Root Port Role for the stack.

3 more elements

In an intermediate network device having a plurality of ports for forwarding network messages within a bridged network, and a stack port for communicating with one or more other intermediate network devices that together form a stack, a method for efficiently transitioning the ports among a plurality of spanning tree protocol (STP) states, the method comprising the steps of:

executing the STP so as to assign the stack port to a Root Port Role;
transitioning the stack port, which has been assigned to the Root Port Role, to a forwarding STP state;
designating all non-stack ports that provide connectivity to the root as Alternate Stack Root Ports;
transitioning the Alternate Stack Root Ports to a discarding STP state;
and
in response to receiving from a source intermediate network device a proposal Bridge Protocol Data Unit (BPDU) message on the stack port that specifies a path cost to the root and that seeks to transition a port of the source device to a forwarding state, issuing one or more Rapid Transition Acknowledgment messages to the source device, provided that the specified path cost of the proposal BPDU is lower than the root path costs associated with the Alternate Stack Root Ports, wherein
the one or more Rapid Transition Acknowledgment messages signal the intermediate network device's agreement to the port of the source device transitioning directly to the forwarding state without transitioning through any intermediary STP states, so that the port of the source device assumes Root Port Role for the stack.

4 more elements

Dependencies are inferred from the claim text.

Cross stack rapid transition protocol

Life of this patent

Cross stack rapid transition protocol

Life of this patent

Abstract

Claims15