HP Network Direr Software Products manual Sizing stage

Key Concepts 97

discovered by the previous detecting devices operation are physically connected together.

The topology process starts when all discovery operations have completed. The topology process is applied to one subnet (or more specifically multinet) at a time.

3Com Network Director uses the term multinet to describe a situation where more than one subnet is attached to a single router port. This can result in devices on different subnets sharing the same switched infrastructure. Consequently, although devices may logically be on different subnets they may learn the MAC addresses of the devices on the other subnet(s) in their bridge tables. Switches learning the MAC addresses of other switches is an important concept in determining the network topology.

The topology algorithm uses Bridge Forwarding Database (FDB) tables to determine on which ports a switch has learned the MAC addresses of other switches in the network. It uses the information of switch ports that have learned the addresses of other switches in order to build a tree of network devices representing the physically connectivity. In reality, each subnet/multinet may not physically appear to be a tree, for instance if spanning tree is used to employ resilient paths. The algorithm used to deduce the topology takes such scenarios into consideration.

Before the tree-building process can take place 3Com Network Director needs to obtain the list of learned addresses for each switch. In practice this involves more than just reading the FDB tables, as different device types have different port and unit numbering schemes. For efficiency purposes an initial attempt is made to determine the positions of most of the end stations. This is done by checking for ports that have only learned the address of a single device that is not a switch. Because the positions of many end stations are resolved here, the amount of information required to be read from the switches is reduced. A summary of the main topology stages is given below.

Unlike the discovery stages described in the previous section these stages are all represented on a single progress bar in the Network Discovery Progress dialog box.

Sizing stage

This stage determines the units and ports that belong to each switch. It establishes which ports have a link present so that it knows which ports