Configuring the Transparent BridgeUse the Bridging General window to set global bridge settings. These parameters allow you to configure the Spanning Tree Protocol and to enable IPX translation. Configuring the Spanning Tree ProtocolInfluencing the Selection of the Root BridgeThe root bridge is selected based on a value that is the combination of a bridge's address and a number you can assign that is the bridge's priority. A lower number for bridge priority makes it likely that the bridge is selected as the root. Influencing the Selection of the Root PortThe root port on a bridge is selected based on which port provides access to the root bridge at the lowest path cost and the relative priority of each port. You can choose either to set the path cost for a port manually through the CLI or allow the Spanning Tree Protocol (STP) to do so automatically. If the spanning tree sets the path cost, the value it assigns is based on the line speed associated with the port. The higher the line speed, the lower the assigned cost. Using Rate Limiting to Minimize the Effects of Broadcast StormsRate limiting is used to minimize the effects of broadcast storms. A broadcast storm is typically caused when a host system responds to multicast packets that are circulating continuously on the network, or when it tries to respond to another system that never replies. The generation of such traffic at an uncontrolled rate can severely affect the available bandwidth on a network, perhaps making communications impossible. You can limit broadcast storms to that segment of the network from which the packets are generated. You do so by setting the maximum number of multicast packets per second that the line card is to forward. The rate you set is applied only if rate limiting is enabled. If the maximum number of packets per second is reached, the line card forwards packets at the specified maximum rate, thereby limiting the effect of the broadcast storm on the other side of the line card. Detecting Changes in Network TopologyCaution: Do not alter the Spanning Tree Protocol default settings associated with the following tasks until you fully understand the effect the change will have on the bridge network. Detecting a Failed Bridge or LinkUse the Max Age parameter to fine-tune the Spanning Tree Protocol's ability to detect a change in topology that is the result of a failed bridge or link. If the time since a bridge last received a Hello Message on a port exceeds the Max Age setting, perhaps the result of a failed link, the bridge recalculates the root, path cost, and root port. Note: Although you can configure each bridge in a spanning tree with a different value for Max Age, the value configured on the root bridge is used by all bridges in the spanning tree. The values configured on non-root bridges are used only if a non-root bridge subsequently becomes root. The lower the Max Age value, the earlier a failed bridge or link may be detected. However, if the Max Age time is exceeded due to a normal drop in network activity and not because of a link or bridge failure, the result may be failure to compute a correct spanning tree. This may cause forwarding loops and severe network congestion. Preventing Forwarding Loops Between BridgesUse the Forward Delay parameter to prevent temporary forwarding loops between bridges. If a temporary forwarding loop occurs, it can cause severe network congestion. The forward delay must be at least twice the maximum amount of time it takes for data to traverse the network. Setting Hello Time, Max Age, and Forward DelayThere is a functional relationship among Hello Time, Bridge Max Age, and Bridge Forward Delay. That relationship requires that the values set for the three parameters conform to the following algorithm: (2) * (Bridge Forward Delay - 1 second) and Bridge Max Age Determining Whether to Enable or Disable IPX TranslationIPX translation is a peer-to-peer networking protocol for Novell NetWare. You may need to enable IPX translation on a line card under the following circumstances:
Translation is necessary in the above conditions because the FDDI-attached NetWare node cannot recognize raw frames, while the Ethernet-attached nodes are configured to recognize only raw frames. For all these nodes to communicate, the line cards can be configured to translate between raw format (on the Ethernet LAN) and SNAP format (on the FDDI LAN). See IPX translation rules for more information. Field Descriptions
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