3com 2500 User Guide

C

HAPTER

 2: VLAN

S

 

ON

 

THE

 C

ORE

B

UILDER 

2500 S

YSTEM

The following example shows how flooding occurs according to VLANs 
set up by protocol. The example assumes an 18-port switch.

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.

1

Default

1 — 18

2

IP

1 — 12

3

IPX

11 — 16

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.

1

Default

1 — 18

2

IP

1 — 10

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.