3Com 2500 manual For example, to create an IP interface that can route through a VLAN

2-8 CHAPTER 2: VLANS ON THE LANPLEX® SYSTEM

Data received on...	Is flooded on...	Because...
IP subnet	VLAN 2	IP network layer matches layer 3 address for
158.103.122.2		VLAN 2.
on port 6
IP subnet	VLAN 3	IP network layer matches layer 3 address for
158.103.123.2		VLAN 3.
on port 6
IP subnet	VLAN 2 and	IP network layer does not match any layer 3
158.103.124.2	VLAN 3	address for IP VLANs.
on port 6
IPX on port 6	VLAN 1	IPX frame does not match any defined VLAN.

As shown in this example, when the subnet address of an IP packet does not match any subnet address of any defined IP VLAN in the system, it is flooded to all of the IP VLANs that share the source switch port, in this case, port 6.

Routing Between The only way for stations that are in two different VLANs to communicate is VLANs to route between them. The LANplex system supports internal routing

among IP, IPX, and AppleTalk VLANs. If VLANs are configured for other routable network layer protocols, they can communicate between them only via an external router.

The LANplex routing model lets you configure routing protocol interfaces based on a VLAN defined for that protocol. To assign a routing interface, you must first create a VLAN for that protocol and then associate it with that interface.

For example, to create an IP interface that can route through a VLAN:

1Create an IP VLAN for a group of switch ports.

This IP VLAN does not need to contain layer 3 information unless you want to further restrict flooding according to the layer 3 subnet address.

2Configure an IP interface with a network address, subnet mask, broadcast address, cost, and type (VLAN). Select an IP VLAN to “bind” to that IP interface.