Cisco Systems BC-109 manual Limit the Maximum SRB Hops

Configure Source-Route Bridging

To create a bridge group that runs an automatic spanning-tree function compatible with the IBM SRB spanning-tree implementation, use the following command in global configuration mode:

Command	Purpose
bridge bridge-groupprotocol ibm	Create a bridge group that runs the
	automatic spanning-tree function.

To enable the automatic spanning-tree function for a specified group of bridged interfaces, use the following command in interface configuration mode:

Command	Purpose
source-bridge spanning bridge-group	Enable the automatic spanning-tree
	function on a group of bridged
	interfaces.

To assign a path cost for a specified interface, use the following command in interface configuration mode:

Command	Purpose
source-bridge spanning bridge-grouppath-cost path-cost	Assign a path cost for a specified
	group of bridged interfaces.

Note Ports running IEEE and IBM protocols form a spanning tree together on the LAN, but they do not mix in the router itself. Make sure the configurations are correct and that each LAN runs only one protocol.

See the end of this chapter for an example of source-route bridging with the automatic spanning-tree function enabled.

Limit the Maximum SRB Hops

You can minimize explorer storms if you limit the maximum number of source-route bridge hops. For example, if the largest number of hops in the best route between two end stations is six, it might be appropriate to limit the maximum source-route bridging hops to six to eliminate unnecessary traffic. This setting affects spanning-tree explorers and all-routes explorers sent from source devices.

To limit the number of SRB hops, use one of the following commands in interface configuration mode:

Command	Purpose
source-bridge max-hops count	Control the forwarding or blocking of
	all-routes explorer frames received
	on this interface.
source-bridge max-in-hops count	Control the forwarding or blocking of
	spanning-tree explorer frames
	received on this interface.
source-bridge max-out-hops count	Control the forwarding or blocking of
	spanning-tree explorer frames sent
	from this interface.

BC-116Bridging and IBM Networking Configuration Guide