This article applies to:

• Threat Analysis Reporter

Question:

• TAR Bandwidth Gauges register zero activity

Procedure:

The fix is for the user to turn off the Auto MDI/MDI-X feature for the ports connected to a TAP. If the user’s switch is not capable of this, the switch will need to be replaced. If the user don't have Auto MDI/MDI-X feature enable on the switch. Or after turn off the Auto MDI/MDI-X feature problem still exist. Please contact Technical Support.

Notes:

MDI (Medium Dependent Interface port)

Also called an "uplink port," it is a port on a network hub or switch used to connect to other hubs or switches without requiring a crossover cable. The MDI port does not cross the transmit and receive lines, which is done by the regular MDI-X ports that connect to end stations (the X stands for "crossed"). The MDI port connects to the MDI-X port on the other device. There are typically one or two ports on a device that can be toggled between MDI (not crossed) and MDI-X (crossed).

Automatic MDI/MDI-X
Some time ago, automatic line sensing was developed within Ethernet, which detects whether the crossover is needed or not. Referred to as "auto MDI/MDI-X," "universal cable recognition" and "auto sensing," it eliminates having separate MDI and MDI-X ports, selector switches and special crossover cables on the equipment.

Based on the above definitions, it appears all should be well, BUT if the Auto MDI/MDI-X feature is turned on, the switch can randomly reverse the cable connection (due to a cable change, switch reset, line down/line up sequence, etc.).  A network tap cannot cope with this connection reversal and is rendered inoperable.