Intel IXM5414E manual Unidirectional link, 270

A

Discarded

Half-duplex Root

Port 1 Port 2

BPDUs

Collision

Port 1 Full-duplex C

Designated

Port 1

B

Port 2 Port 2

Blocked

In the preceding example, port 1 on bridge B is configured as a full-duplex port and port 1 on bridge A is either configured as a half-duplex port or is left in auto-negotiation mode. Because port 1 on bridge B is configured as a full-duplex port, it does not test for carrier sense when accessing the link. Bridge B will then start sending packets even if bridge A is using the link. A will then detect collisions and begin to run the flow control algorithm. If there is enough traffic between bridges B and A, all packets (including BPDUs) will be dropped. If the BPDUs sent from bridge A to bridge B are dropped for longer than the Max. Age, bridge B will lose its connection to the root (bridge A) and will unblock its connection to bridge C. This will create a data loop.

Unidirectional link

Unidirectional links can be caused by an undetected failure in one side of a fiber cable or by a problem with a port’s transceiver. Any failure that enables a link to remain up while providing one- way communication is very likely to cause a Spanning Tree Protocol failure.

A

Root

Port 1 Port 2

Port 1 B C

Designated

Port 1

Port 2 Port 2

BPDUs Lost

Blocked

270 Intel® Blade Server Ethernet Switch Module IXM5414E