HP Network Direr Software Products manual Spanning Tree stage, Remote Poll Stage broadcast ARP

98CHAPTER 4: DISCOVERING THE NETWORK

to consider during topology. Since the detecting devices operation has already sized each device, it does not need to communicate with the devices again.

Information obtained from the devices is also used to establish whether they are supported by 3Com Network Director. For instance, it checks the agent version, VLAN configuration along with other parameters. Warnings are logged in the Discovery report. For non-3Com devices an attempt is made to use standard MIBs when considering them as part of the topology process. Since different devices use differing numbering schemes for units and ports and often use proprietary MIBs, the information displayed about the topology of third party devices will not be as detailed as that of 3Com ones, and sometimes may not be as accurate.

Spanning Tree stage

Having obtained a list of supported switches, this stage attempts to determine those whose spanning tree links are blocked. This information is generally provided by standard bridge MIBs. This is an extension of the Device Sizing stage, but the information obtained is only required for topology.

The ports participating in such links are eliminated from the remainder of the topology process until the tree-building stage.

Remote Poll Stage (broadcast ARP)

The purpose of this stage is to attempt to force each switch to learn the addresses of other switches on the same subnet/multinet. It uses remote poll to instruct each switch to ping an unused address on the subnet, thus forcing it to transmit a broadcast ARP. This causes other switches on the subnet to learn the addresses of the source switch.

Remote Poll, sometimes called Remote Ping, is a mechanism, using SNMP, to instruct a device to ping another IP address. This requires an SNMP set instruction to be sent to the device, which relies on 3Com Network Director having correctly determined the SNMP write community string during the Device Capabilities Detection stage. If the write community string has not been correctly established or the device does not support the remote poll feature (e.g. third party devices) then the accuracy of the deduced topology may be reduced.