User Guide

Key Considerations 573
appear on one port on one VLAN and on another port on another VLAN,
on the same switch e.g.:
Figure 313 Coexistent MAC Address
This causes 3Com Network Director problems when it tries to construct
its map of the network. The algorithm that 3Com Network Director uses
to construct the map assumes that the network can be represented by a
tree of devices with no loops in the network. However, Figure 313
contravenes this assumption. To the switch, it appears as if there is a loop
in the network because MAC A has been learned on 2 different ports.
The 3Com Network Director map-building algorithm does not handle
loops such as this. Instead the map-building algorithm picks one port for
each MAC address and ignores all other ports that it has been learned on.
So in the above example, pick port 1 and ignore port 24. However, this
may result in 3Com Network Director building a network map that is not
completely accurate. In this situation, 3Com Network Director adds the
following warning to the Discovery Report. See “
The Discovery Report”
on page 131
.
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.
Table 84 Device Learned On Multiple Ports
This warning will only occur due to particular combinations of network
topology and VLAN configuration, and so this situation will be fairly
uncommon.
Device Learned On
Multiple Ports
Learned By Device Ports Learned On
Switch 3300 Switch4400-6 Port 1
Port 5
00-30-1e-c6-40-38 Switch4400-6 Port 13
Port 3