Dell 6200 manual Operation In The Network, April, Small Bridged Network, Single STP Topology

MSTP INTEROPERABILITY OF THE DELL™ POWERCONNECT™ 6200 SERIES SWITCHES WITH CISCO IOS AND CISCO CATOS-BASED SWITCHES

OPERATION IN THE NETWORK

In the following diagram of a small, 802.1d bridged network, STP is necessary to create an environment with full connectivity and without loops:

Figure 4: Small Bridged Network

Assume that bridge BrA is elected to be the Root Bridge, and Port Pt1 on bridge BrB and BrC are calculated to be the root ports for those bridges, Port Pt2 on bridge BrB and BrC would be placed into Blocking State. A loop-free topology would then exist. End stations in VLAN 10 could talk to other devices in VLAN 10 and end stations in VLAN 20 would only have a single path to communicate with other VLAN 20 devices. The logical single STP network topology would look something like this:

Figure 5: Single STP Topology

For VLAN 10, this Single STP Topology is fine and presents no limitations or inefficiencies. On the other hand, VLAN 20’s traffic pattern is inefficient. All frames from bridge BrB will have to traverse a path through bridge BrA before arriving at bridge BrC. If the ports Pt2 on bridge BrB and BrC could be used, these inefficiencies could be eliminated. MSTP does just that by allowing the configuration of MSTIs based upon a VLAN or groups of VLANs.

APRIL 2008 7