Cabletron Systems 7C04-R Defining Your Connection Policy, Special Ring Configurations, Dual Homing

FDDI Management

Each interface controls only its own connection policy; however, when two interfaces attempt to connect, their combined connection policies dictate the connections that will be allowed, with the most lenient policy prevailing — in other words, all connections (except for the illegal M—>M connection) are allowed unless forbidden by both connecting nodes. For example, if you disallow the A—>M connection on one node, but attempt to make that connection with another node which does not forbid it, the connection will be allowed.

Special Ring Configurations

You can use the SMT Connection Policy window to allow or prevent the following ring configurations:

Dual Homing

Dual homing is a method of configuring concentrators with a redundant topology that provides a backup data path to protect critical devices from losing contact with the main ring; dual homing also achieves a kind of separation from the main ring that makes it easy to bring a critical device down for maintenance without causing widespread ring failure.

To achieve a dual homing configuration, connect the A port of your critical device to an M port on one dual-attached concentrator (DAC), and connect the B port of the same device to an M port on another DAC. SMT will automatically make the B—>M connection active and place the A—>M connection in stand-by; the A—>M connection will only become active if the B—>M connection should fail. (Once the B—>M connection is restored, it is automatically re-activated, and the A—>M connection goes back into standby mode.) Dual homing will not be permitted if either the A—>M or B—>M connections have been disallowed for all involved nodes.

Twisted Ring

When an FDDI ring is in a twisted configuration, at least one station is supporting both an A—>A connection and a B—>B connection; in this configuration, the station with the A—>A and B—>B connections is actually residing on the secondary FDDI ring, and is therefore isolated from the stations on the primary ring. A wrap condition on a twisted ring will bring the isolated station back into contact with any stations still connected to the primary ring. You can prevent a twisted ring configuration by disallowing the A—>A and/or the B—>B connections for all nodes.

Defining Your Connection Policy

To configure the connection policy for the selected interface:

1.To disallow any connection types, click mouse button 1 on the appropriate selection box or boxes; to allow connections which have been previously disallowed (except for the illegal M—>Mconnection), click on the selection box again.

Configuring the SMT Connection Policy 4-23