10-11
Bridging—Transmitting Non-IP Traffic or Merging Two Networks
Configuring Spanning Tree
6. Verify that all hosts participating in a bridge group are on the same subnet.
You can also try viewing the bridge table. If the table does not show entries
for an interface, this is a good hint that the devices on the other end of
that connection are on a different subnet.
7. The bridge runs more smoothly if you remove IP addresses from every
interface in the bridge except one. For example, you can assign only the
Ethernet interface an IP address. Enter show ip interfaces and verify
that WAN interfaces in the bridge group do no have IP addresses.
Configuring Spanning Tree
When the router acts as a bridge, it automatically enables Rapid Spanning Tree
Protocol (RSTP), or IEEE 802.1W. RSTP eliminates network loops and is fully
backwards compatible with Spanning Tree Protocol (STP), or IEEE 802.D.
The router only supports RSTP and STP when it acts as a bridge. The following
interfaces join the spanning tree when they join a bridge group:
■ Ethernet interfaces
■ Frame Relay subinterfaces
■ ATM subinterfaces
Often, the router will be able to run RSTP adequately without additional
configuration: the default settings match most WAN topologies.
You can configure spanning tree functions on the router in order to:
■ raise the router’s priority for being elected root device
■ change the cost of a connection
■ connect the router to an edge device
■ connect the router to a hub
■ have the router run STP
Configuring spanning tree on a WAN router is usually simpler than configuring
it on a switch. A switch might provide many connections—some redundant,
some necessary, some faster, some slower, some to end users, some to another
switch, some to a hub. The ProCurve Secure Router typically has fewer
connections—and these only to other routers and switches—and is part of
few or no loops. Therefore, you need not understand STP and RSTP in great
technical depth.
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