Enterasys Vertical Horizon VH-2402S2 Spécifications télécharger pdf (Page 129)

9033691-01 VH-2402-L3 Management Guide 121

When STP is enabled using the default parameters, the path

between source and destination stations in a switched

network might not be ideal. For instance, connecting higher-

speed links to a port that has a higher number than the

current root port can cause a root-port change. The goal is

to make the fastest link the root port.

STP Port States

The BPDUs take some time to pass through a network. This

propagation delay can result in topology changes where a

port that transitioned directly from a Blocking state to a

Forwarding state could create temporary data loops. Ports

must wait for new network topology information to propagate

throughout the network before starting to forward packets.

They must also wait for the packet lifetime to expire for

BPDU packets that were forwarded based on the old

topology. The forward delay timer is used to allow the

network topology to stabilize after a topology change.

In addition, STP specifies a series of states a port must

transition through to further ensure that a stable network

topology is created after a topology change.

Each port on a switch using STP exists is in one of the

following five states:

• Blocking – the port is blocked from forwarding or receiving

packets

• Listening – the port is waiting to receive BPDU packets that

may tell the port to go back to the blocking state

• Learning – the port is adding addresses to its forwarding

database, but not yet forwarding packets

• Forwarding – the port is forwarding packets

• Disabled – the port only responds to network management

messages and must return to the blocking state first

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Enterasys Vertical Horizon VH-2402S2 Spécifications Page 129