Fast-uplink troubleshooting

Some of the problems that can result from incorrect use of fast-uplink MSTP include temporary loops and generation of duplicate packets.

Problem sources can include:

• Fast-uplink is configured on a switch that is the MSTP root device.

• Either the Hello Time or the Max Age setting (or both) is too long on one or more switches. Return the Hello Time and Max Age settings to their default values (2 seconds and 20 seconds, respectively, on a switch).

• A "downlink" port is connected to a switch that is further away (in hop count) from the root device than the switch port on which fast-uplink MSTP is configured.

• Two edge switches are directly linked to each other with a fast-uplink (Mode = Uplink) connection.

• Fast uplink is configured on both ends of a link.

• A switch serving as a backup MSTP root switch has ports configured for fast-uplink MSTP and has become the root device because of a failure in the original root device.