3Com CoreBuilder 2500 - VLAN Exception Flooding

2-6 CHAPTER 2: VLANS ON THE COREBUILDER 2500 SYSTEM
The following example shows how flooding occurs according to VLANs
set up by protocol. The example assumes an 18-port switch.
VLAN Exception
Flooding
Data for a protocol may arrive on a switch port that has no defined VLAN
for that protocol. In such cases, called VLAN exception flooding, the
default VLAN defines the flooding domain for the data, even if a VLAN
for the protocol exists elsewhere in the system.
The following example shows how VLAN exception flooding occurs. The
example assumes an 18-port switch.
VLAN Index VLAN Protocol VLAN Ports
1 Default 1 — 18
2 IP 1 — 12
3 IPX 11 — 16
Data received on
this port
Is flooded on
this VLAN
Because
IP — port 1 VLAN 2 The received IP data matches the IP VLAN
on the source port.
IPX — port 11 VLAN 3 The received IPX data matches the IPX
VLAN on the source port.
XNS — port 1 VLAN 1 The received XNS data matches no
protocol VLAN, so the default VLAN is
used.
VLAN Index VLAN Protocol VLAN Ports
1 Default 1 — 18
2 IP 1 — 10
Data received on
this port
Is flooded on
this VLAN
Because
XNS — port 1 VLAN 1 The received XNS data does not match any
defined VLAN in the system.
IP — port 2 VLAN 2 The received IP data matches IP VLAN 2 for
source ports 1 through 10.
IP — port 12 VLAN 1 The received IP data on source port 12
does not match any defined source port
for IP VLAN, so the default VLAN is used.