3Com 3C15500 - Network Director User Manual page 153

Discovery Report Errors and Warnings 149
The following devices have support for the Spanning Tree Protocol
enabled. Links connected to these devices may in the future be
blocked by the Spanning Tree Protocol. 3Com Network Director
may not be able to detect this occurring.
Some third party devices do not provide suitable MIB support to allow
3Com Network Director to initially determine and subsequently track
changes in spanning tree topology, or provide a non-standard
implementation. As a result, the topology that 3Com Network Director
depicts may not be accurate.
A device has been seen (or "learned") on multiple ports of another
device. This implies there is a loop in the network. 3Com Network
Director may not represent the topology of the network
accurately.
Changes in network topology, such as a wireless device moving from one
wireless access point to another, or changes in spanning tree topology,
may result in a device being seen to move ports on another device. If this
occurs during Network Discovery then 3Com Network Director may not
be able to depict the topology of the network accurately.
It is usually possible to address this issue by rediscovering the subnet or
subnets of the devices in question.
The following devices have a device performing ARP proxies for
them.
If you have a 3Com SuperStack 3 Firewall in your network that is
operating in transparent mode then any ARP requests sent to devices on
the other side of the firewall will be handled by the firewall itself and it
will respond with the MAC address of the firewall. In addition the
firewall will substitute its MAC address as the source address in any
packets it receives that are destined for an IP address on the other side of
the firewall. This technique is known as ARP proxy.
3Com Network Director is unable to determine the MAC addresses of
devices on the other side of a 3Com SuperStack 3 Firewall, but is able to
identify the IP addresses of such devices. As a result, 3Com Network
Director may not be able to depict the topology of the network
accurately.
3Com Network Director could not determine a speed for at least
one interface on the following devices.