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This appendix explains how connecting the hubs to each other plays a role in managing a stack of FastHub 400 models. This appendix provides the following information:
You can interconnect hubs by connecting them via the stacking connectors on the rear panel of the hubs. The interconnected hubs in the hub stack appear to the rest of the network and to the management interface as a single logical repeater.
Interconnecting hubs differs from cascading hubs, which are connected via the standard 10/100 ports on the front of the hub. The connected hubs then appear to the rest of the network and to the management interface as two logical repeaters.
Figure C-1 shows four interconnected hubs creating a logical repeater with a maximum of 96 ports in the stack and two cascading hubs creating two logical repeaters with a maximum of 48 ports.
You can use Class II repeaters to build networks with two or more repeaters or hub stacks in a single collision domain. With two Class II repeaters, you can have a short cable segment connecting the repeaters while maintaining 100-meter Category 5 connections to the attached stations. Using more than two repeaters in a single collision domain requires considerably shorter connections to attached stations. Figure C-2 shows the connection of two hub stacks through the front-panel 10/100 ports to form a collision domain with up to 190 ports.
You can interconnect up to four FastHub 400 models to build a hub stack by using the stacking cables and the stacking connectors on the rear panel of the hubs. The stacking cables can be ordered separately (model number WS-C400-CAB-EXP).
Use the following guidelines when connecting the stacking cables:
 | Caution Make sure the cable connector is properly aligned before inserting it into the stacking connector. Inserting the connector at an angle damages the pins, making the cable unusable. |
FastHub 400 models can be added to or removed from the hub stack without powering down any hub in the stack. This is referred to as hot swapping. The stack reconfigures itself in approximately 30 seconds. If you power down a hub in the middle of the stack and keep it interconnected to the stack, the hubs above and below it continue to communicate.
| Caution If you are removing a management hub and there is no secondary management hub in the stack, you lose manageability for the entire hub stack. In addition, if the removed management hub is mounted between two operating hubs, you split the Ethernet segment into two separate segments when the stacking cables are disconnected. |
Follow these steps to remove the hub:
Step 1 On the hub being removed, disconnect the stacking cable from either the DOWN or UP connectors or from both connectors.
Step 2 Remove the hub from the rack or tabletop.
You need at least one FastHub 400M model per three interconnected hubs (one hub stack) if you want to manage the stack. A second FastHub 400M model in the stack can act as a redundant stack manager in case the primary manager fails.
If a hub stack has more than one management hub, the upper management hub in the stack is the primary management hub. The lower management hub is the secondary management hub.
To manage the hub stack, you can use the system information (such as the IP, CDP, and SNMP information) assigned to the primary management hub. The primary management hub also stores the port settings of each hub in the stack. If the primary management hub becomes inactive or is disconnected from the stack, the secondary management hub becomes the primary management hub and uses the same stack information.
| Caution If you are removing a management hub and there is no secondary management hub in the stack, you lose manageability for the entire hub stack. In addition, if the removed management hub is mounted between two operating hubs, you split the Ethernet segment into two separate segments when the stacking cables are disconnected. |
For information on managing the hub stack through the hub manager, see the "Managing the Hub Segments" section.
The physical position of the hubs in the hub stack and the stacking cable connections between hubs determine how they appear to the management interface. The FastHub management interface uses a hub-numbering convention, assigning numbers from top to bottom---the hub at the top of the stack is Group 1, the hub below Group 1 is Group 2, and so on (see Figure C-3). If you have four hubs in a stack and you remove Group 3 and connect the stacking cable from Group 2 to Group 4, Group 4 is renumbered as Group 3.
If a hub stack has more than one management hub, the upper management hub in the stack is the primary management hub. The lower management hub is the secondary management hub. For more information, see the "Managing a Hub Stack" section.
Posted: Wed Feb 24 10:58:36 PST 1999
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