3Com corebuilder 3500 Implementation Manual page 201

Example 2: VLAN Exception Flooding
If an untagged frame arrives on an untagged bridge port that belongs to
a VLAN that matches the protocol type of the incoming frame, the frame
is assigned to the matching VLAN. The default VLAN (if it exists) provides
the match and defines the flooding domain for the data when other
VLANs that match the frame's protocol type are defined in the system but
not on the receive port. This case is called VLAN exception flooding.
Table 25 shows how the VLAN exception flooding decision is made
(assuming a 12-port configuration).
Table 25 VLAN Exception Flooding
Index VID
1 1
2 2
Untagged data
received on this Is flooded on
port this VLAN
XNS - port 1 Default, VID 1
IP - port 2 IP1, VID 2
IP - port 12 Default, VID 1
Rules of VLAN Operation
VLAN Name Ports
Default 1 – 12
IP1 1 – 8
Because
XNS data on port 1 matches the
unspecified protocol of the default VLAN
on port 1.
IP data received matches IP1 for source
ports 1 – 8.
IP data on port 12 matches the
unspecified protocol of the default VLAN
on port 12.
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