Spanning Tree Stage; Remote Poll Stage (Broadcast Arp) - 3Com 3C15500 - Network Director User Manual

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HAPTER ISCOVERING THE ETWORK
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.