Cisco Systems BC-109 manual Enable the Automatic Spanning-Tree Function

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Enable the Automatic Spanning-Tree Function

Forwarding all-routes explorer packets is the default. However, in complicated source-route bridging topologies, using this default can generate an exponentially large number of explorers that are traversing the network. The number of explorer packets becomes quite large because duplicate explorer packets are sent across the network to every node on every path. Eventually each explorer packet will reach the destination device. The destination device will respond to each of these explorer packets. It is from these responses that the source device will collect the RIF and determine which route it will use to communicate with the destination device. Usually, the route contained in the first returned response will be used.

The number of explorer packets traversing the network can be reduced by sending spanning-tree explorer packets. Spanning-tree explorer packets are sent to specific nodes; that is, to only the nodes on the spanning tree, not to all nodes in the network. You must manually configure the spanning-tree topology over which the spanning-tree explorers are sent. You do this by configuring which interfaces on the routers will forward spanning-tree explorers and which interfaces will block them.

To enable forwarding of spanning-tree explorers on an outgoing interface, use the following command in interface configuration mode:

Command

Purpose

source-bridge spanning

Enable the forwarding of

 

spanning-tree explorer packets on an

 

interface.

 

 

Note While enabling the forwarding of spanning-tree explorer packets is not an absolute requirement, it is strongly recommended in complex topologies. Configuring an interface to block or forward spanning-tree explorers has no effect on how that interface handles all-routes explorer packets. All-routes explorers can always traverse the network.

To block forwarding of spanning tree explorers on an outgoing interface, use the following command in interface configuration mode:

Command

Purpose

no source-bridge spanning

Block spanning-tree explorer packets

 

on an interface.

 

 

Enable the Automatic Spanning-Tree Function

The automatic spanning-tree function supports automatic resolution of spanning trees in SRB networks, which provides a single path for spanning explorer frames to traverse from a given node in the network to another. Spanning explorer frames have a single-route broadcast indicator set in the routing information field. Port identifiers consist of ring numbers and bridge numbers associated with the ports. The spanning-tree algorithm for SRB does not support Topology Change Notification bridge protocol data unit (BDPU).

Note Although the automatic spanning-tree function can be configured with source-route translational bridging (SR/TLB), the SRB domain and transparent bridging domain have separate spanning trees. Each Token Ring interface can belong to only one spanning tree. Only one bridge group can run the automatic spanning-tree function at a time.

Configuring Source-Route Bridging BC-115

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Contents SRB Configuration Task List Configuring Source-Route BridgingConfigure a Dual-Port Bridge Configure Source-Route BridgingMultiple Dual-Port Bridges Configure a Multiport Bridge Using a Virtual RingSource-bridge ring-group ring-group Define a Ring Group in SRB ContextNo source-bridge ring-group ring-group Source-bridge route-cache cbus Configure SRB over FddiEnable SRB and Assign a Ring Group to an Interface Interface fddi slot/portConfigure SRB over Frame Relay Configure Fast-Switching SRB over FddiEnable the Automatic Spanning-Tree Function Limit the Maximum SRB Hops Enable Use of the RIF Configure Bridging of Routed ProtocolsConfigure the RIF Timeout Interval Configure a Static RIF EntryOverview of SR/TLB Following notes and caveats apply to all uses of SR/TLB No source-bridge transparent ring-group fastswitch Enable Bridging between Transparent Bridging and SRBDisable Fast-Switched SR/TLB Enable Translation Compatibility with IBM 8209 BridgesSource-bridge sap-80d5 dsap Enable Token Ring LLC2-to-Ethernet ConversionEnable 0x80d5 Processing Enable Standard Token Ring LLC2-to-Ethernet LLC2 ConversionConfigure NetBIOS Support Source-bridge proxy-netbios-only Specify Timeout and Enable NetBIOS Name CachingSpecify Dead-Time Intervals for NetBIOS Packets Configure the NetBIOS Cache Name LengthEnable NetBIOS Proxying Create Static Entries in the NetBIOS Name CacheNetbios name-cache query-timeout seconds Configure LNM SupportNetbios name-cache recognized-timeout seconds LNM Linking to a Source-Route Bridge on Each Local Ring LAN Network Manager Monitoring and Translating How a Router Works with LNMDisable LNM Functionality Enable Other LRMs to Change Router Parameters Disable Automatic Report Path Trace FunctionEnable LNM Servers Apply a Password to an LNM Reporting LinkChange Reporting Thresholds Monitor LNM Operation Change an LNM Reporting IntervalLnm softerr milliseconds Configure NetBIOS Access Filters Using Station Names Configure NetBIOS Access FiltersSecure the SRB Network Netbios input-access-filter bytes name Configure NetBIOS Access Filters Using a Byte OffsetNetbios access-list host name permit deny pattern Netbios access-list bytes name permit deny offsetNetbios output-access-filter bytes name Configure Administrative Filters for Token Ring TrafficFilter Frames by Protocol Type Filter Source Addresses Filter Frames by Vendor CodeFilter Destination Addresses Access Expression Example Optimize Access Expressions Configure Access ExpressionsTune the SRB Network Alter Access Lists Used in Access ExpressionsEnable or Disable the Source-Route Fast-Switching Cache Establish the Connection Timeout Interval Enable or Disable the SSEOptimize Explorer Processing Controlling Explorer Storms in Redundant Network Topologies Establish SRB Interoperability with TI MAC Firmware Configure Proxy ExplorersMac-address ieee-address Monitor and Maintain the SRB Network Report Spurious Frame-Copied ErrorsSource-bridge tcp-queue-max number SRB Configuration ExamplesBasic SRB with Spanning-Tree Explorers Example Dual-Port Source-Route Bridge ConfigurationSRB-Only Example Optimized Explorer Processing Configuration ExampleMultiport SRB Example SRB and Routing Certain Protocols ExampleSRB with Multiple Virtual Ring Groups Example Configuration for Router aRouter a SRB over Fddi Configuration ExamplesSRB over Fddi Fast-Switching Example Configuration for Router BFrad Using SRB over Frame Relay to Connect to a Cisco Router SRB over Frame Relay Configuration ExampleAdding a Static RIF Cache Entry Example Configuration of Router aConfiguration on Router B Configuration on Router CSR/TLB for a Simple Network Example Adding a Static RIF Cache Entry for a Two-Hop Path ExampleBC-154Bridging and IBM Networking Configuration Guide Example of a Bit-Swapped Address SR/TLB with Access Filtering ExampleSpecifying a Static Entry NetBIOS Support with a Static NetBIOS Cache Entry ExampleLNM for a Simple Network Example Wayfarer# show lnm configLNM for a More Complex Network Example NetBIOS Access Filters Example Filtering Bridged Token Ring Packets to IBM Machines Example Shows a router connecting four Token Rings Following access expression would result Creating Access Filters ExampleFast-Switching Example Access Filters ExampleAutonomous Switching Example
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