3Com LinkBuilder FMSII Bridge Managment Module

The LinkBuilder FMS II Bridge/Management Module (3C16040)

Product Overview

The Bridge/Management Module is a two port IEEE 802.1 D Revision 9 compliant bridge, which has been designed to slot into the FMS II product range. One port (i.e. the Internal Bridge Port) is connected to the FMS bus. The other port (i.e. the External Bridge Port) connects the bridge to the external network.

In addition to the bridging functionality, the Bridge/Management Module also provides facilities to manage the FMS II repeater functionality. SmartAgent software in the Bridge/Management Module automatically gathers and collates information about the stack.

The Bridge/Management Module supports the Simple Network Management Protocol (SNMP). As well as supporting in-band management via SNMP and a network link, the Bridge/Management Module has a serial port which allows out-of-band management.

The Bridge/Management Module performs the following functions:

Bridge Operation

• Network Segmentation

  Using a process known as Address-Based Filtering of Frames, a bridge can reduce network overload by preventing the unnecessary passing of MAC frames from one side of the bridge to the other.

  Network segmentation reduces unnecessary use of the bandwidth and can greatly increase network performance. Network segmentation also enables you to set up workgroups.

• Resilience

  The Bridge/Management Module supports the Spanning Tree Algorithm and Protocol (known simply as Spanning Tree). Spanning Tree detects and eliminates loops created by duplicate paths between network nodes. If more than one path exists, Spanning Tree ensures that only one of the paths is active. The inactive path acts as a backup path to provide resilience against bridge failure and network failure. When the Spanning Tree detects a path or bridge failure it automatically activates the backup path or bridge.

• Increased Network Integrity

  The bridge halts the propagation of certain errors around the network, e.g. illegal frames. The bridge will discard frames received with detected errors and excessive broadcast traffic.

• LAN Extension

  The bridge increases the physical extent of the LAN (Local Area Network) by connecting two adjacent IEEE 802.3 LANs to form one Extended LAN. The bridge supports 'Transparent Bridging' as defined by the IEEE 802.1 D Revision 9 standard.

Network Management

• Configuration

  The management facilities provided by the Bridge/Management Module offer you the opportunity to change the set up and configuration of FMS II stacks.

• Performance Monitoring

  The FMS II network performance monitoring facilities enable you to perform forward planning and early fault detection.

• Resilience

  In addition to the resilience provided by the Spanning Tree, FMS repeater ports can also be configured to provide resilient links. When the main link in the resilient link pair fails a standby link will automatically come into operation to ensure that data loss is minimized.

• Security

  The Bridge/Management Module provides security measures which prevent unwanted access to the FMS II management facilities, i.e. each user is assigned an access level that determines which management parameters the user can view or modify.

• Status Monitoring

  The operating status of the FMS II unit can be monitored using the management facilities of the Bridge/Management Module. The operating status of other devices on the network can be monitored using the Remote Poll facility.
   

How This Bridge Works

The bridge connects two adjacent IEEE 802.3 LANs to form one Extended LAN. The bridge uses 'Transparent Bridging' as defined by the IEEE 802.1 D Revision 9 standard.

A bridge examines the source addresses of frames received on its ports to build up a picture of which devices are situated on which port. The bridge maintains a Filtering Database, which contains the source MAC Address and the port on which the frame was received.

The bridge examines the destination addresses of the received frames and compares them to addresses held in the Filtering Database.

If a destination address does not match any of the addresses in the Filtering Database, the bridge forwards the frame.

If the address is matched, the port identifier kept along with that address is compared to the port identifier for the received frame. The comparison is made to determine whether the sending device is on the same port as the destination device. If the port identifier is the same (e.g. the sending and destination device are both accessed via the External Bridge Port) the frame is not forwarded to the other port. In this case the frame is said to be 'filtered'. Local traffic is therefore restricted and not passed over the bridge to the rest of the network.

If the port identifier is different (i.e. the destination device is accessed via a different bridge port to the one on which the frame was received) the frame will be forwarded to the other port.

The bridge also examines the source address of a received frame and compares it to addresses in the Filtering Database. If the source address is not already in the Filtering Database, the bridge adds it. In this way the bridge is said to 'learn' the addresses of the devices on the network.