Cabletron Systems TSX-1620 The Filtering Database Window

Using the TSX-1620 Bridge View

MtuExceedDiscard

Mtu stands for “maximum transfer unit”; it is the largest frame size that can be

processed by the TSX-1620. A port discards any received frames that are larger

than the Mtu; this ﬁeld lists how many such frames were discarded.

The information in the Bridge Statistics window is a snapshot of the data. When

you open the Bridge Statistics window, the application polls the devices for

information. Devices are not polled again until you click mouse button 1 on the

Update button, or close, then re-open the Statistics window.

The Filtering Database Window

In Transparent bridging, each bridge port uses the device’s Filtering Database to

determine a packet’s route through the bridge. The Filtering Database is created

from permanent entries made via management, and from entries learned as the

bridge collects and stores the source address and port association from each

packet it receives.

When in the Forwarding state, the bridge examines each received packet and

compares the destination address to the contents of the Filtering Database. If the

destination address is located on the network from which the packet was

received, the bridge ﬁlters (does not forward) the packet. If the destination

address is located on a different network, the bridge forwards the packet to the

appropriate network. If the destination address isn’t found in the Filtering

Database, the bridge forwards the packet to all networks. To keep Filtering

Database entries current, older entries are purged after a period of time, which is

called the Dynamic Ageing Time.

The Filtering Database has two types of entries: Forwarding and Static. The

Forwarding view of the Filtering Database contain addresses that the bridge

learns from network trafﬁc (also known as dynamic entries) as well as all the

static 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 are

purged. Static entries may be subject to the ageing timer, depending on how the

entries were added. Static entries enter the Filtering Database in two ways: either

automatically, when permanent database entries are copied to the Filtering

Database, or manually when you move a Forwarding entry to the Static Table.

NOTE

When a device is reset, statistics windows and/or statistics displays in the Bridge View

windows may display very large numbers for one polling interval. This is due to the

resetting of counters.