3Com 10002211 manual Routing Between VLANs

C-8 APPENDIX C: VLANS ON THE COREBUILDER SYSTEM

Routing Between VLANs

The only way for stations that are in two different VLANs to communicate is to route between them. The CoreBuilder 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 CoreBuilder 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.

If layer 3 information is provided in the IP VLAN for which you are configuring an IP interface, the subnetwork portion of both addresses must be the same.

For Example:

IP VLAN subnet 157.103.54.0 with subnet mask of 255.255.255.0

IP host interface address 157.103.54.254 with subnet mask of 255.255.255.0

Layer 2 (bridging) communication is still possible within an IP VLAN (or router interface) for the group of ports within that IP Interface’s IP VLAN. IP data destined for a different IP subnetwork uses the IP routing interface to get to that different subnetwork, even if the destination subnetwork is on a shared port.