3Com CoreBuilder 3500, Implementation Manual

Page: 180 / 592

180 C
HAPTER
9: V
IRTUAL
LAN
S
This situation causes different behavior for allOpen versus allClosed
VLANs. For example, for allClosed VLANs, if a frame is received on a port
in unspecA with a destination address that is known in the address table
of unspecB, the frame is flooded throughout unspecA because it has an
unknown address for unspecA. For allOpen VLANs, there is one address
table; therefore; the frame is forwarded to the port that corresponds to
the known destination address. However, if the transmit port is not a
member port of unspecA, the frame is transmitted untagged, regardless
of that port’s tag status on unspecB.
In Figure 28, if STP is enabled, STP blocks one of the paths unless you
enable Ignore STP mode. See “Ignore STP Mode” earlier in this chapter
for more information.
Figure 28 Port-based VLANs Without Overlapped Ports
L2/3 L2/3
(Ports 1-4) VID 20, unspecA
Device 1 Device 2
VID 30, unspecB
(Ports 3,5-8)
VID 30, unspecB
100Mb
100Mb