Cabletron Systems TSX-1620 User Manual

Also see for SPECTRUM: User guide User guide User guide User guide Guide

Contents

The Filtering Database Window3-15Using the TSX-1620 Bridge ViewMtuExceedDiscardMtu stands for “maximum transfer unit”; it is the largest frame size that can beprocessed by the TSX-1620. A port discards any received frames that are largerthan the Mtu; this field lists how many such frames were discarded.The information in the Bridge Statistics window is a snapshot of the data. Whenyou open the Bridge Statistics window, the application polls the devices forinformation. Devices are not polled again until you click mouse button 1 on theUpdate button, or close, then re-open the Statistics window.The Filtering Database WindowIn Transparent bridging, each bridge port uses the device’s Filtering Database todetermine a packet’s route through the bridge. The Filtering Database is createdfrom permanent entries made via management, and from entries learned as thebridge collects and stores the source address and port association from eachpacket it receives.When in the Forwarding state, the bridge examines each received packet andcompares the destination address to the contents of the Filtering Database. If thedestination address is located on the network from which the packet wasreceived, the bridge filters (does not forward) the packet. If the destinationaddress is located on a different network, the bridge forwards the packet to theappropriate network. If the destination address isn’t found in the FilteringDatabase, the bridge forwards the packet to all networks. To keep FilteringDatabase entries current, older entries are purged after a period of time, which iscalled the Dynamic Ageing Time.The Filtering Database has two types of entries: Forwarding and Static. TheForwarding view of the Filtering Database contain addresses that the bridgelearns from network traffic (also known as dynamic entries) as well as all thestatic entries. Learned entries are subject to the bridge’s Dynamic Ageing Timer;entries that aren’t accessed within the time specified by the ageing timer arepurged. Static entries may be subject to the ageing timer, depending on how theentries were added. Static entries enter the Filtering Database in two ways: eitherautomatically, when permanent database entries are copied to the FilteringDatabase, or manually when you move a Forwarding entry to the Static Table.NOTEWhen a device is reset, statistics windows and/or statistics displays in the Bridge Viewwindows may display very large numbers for one polling interval. This is due to theresetting of counters.