3com 2500 User Guide

You can assign network layer information to IP VLANs so you can manage 
your VLANs by subnetwork. The CoreBuilder 2500 system makes 
flooding decisions by first matching the incoming frame using the 
protocol (IP) and then matching the frame with Layer 3 subnetwork 
information. If the received data is IP but does not match any defined IP 
subnetwork VLAN, the data is flooded within all IP VLANs using the 
relevant switch port.

For example, you can configure two overlapping IP VLANs for ports 1 
through 10 as follows:

■

IP VLAN 1 — Subnetwork 158.101.112.0, ports 1

 

through

 

10, with 

subnet mask 255.255.255.0

■

 

— Subnetwork 158.101.113.0, ports 1

 

through

 

10, with 

subnet mask 255.255.255.0

The following example shows how flooding decisions are made using 
overlapping IP VLANs. The example assumes a 12-port switch.

1

Default

none

1 – 12

2

IP

158.103.122.0/ 
255.255.255.0

1 – 6

3

IP

158.103.123.0/ 
255.255.255.0

6 – 12

IP subnetwork 
158.103.122.2 
on port 6

VLAN 2

The IP network layer matches the Layer 3 
address for VLAN 2.

IP subnetwork 
158.103.123.2 
on port 6

VLAN 3

The IP network layer matches the Layer 3 
address for VLAN 3.

IP subnetwork 
158.103.124.2 
on port 6

VLAN 2 and 
VLAN 3

The IP network layer does not match any 
Layer 3 address for IP VLANs.

IPX on port 6

VLAN 1

The IPX frame does not match any defined 
VLAN.