InterVLAN Routing

VLANs divide the network into smaller broadcast domains, but also prohibit communication between domains To enable communication between those groups—without also passing broadcasts—routing is used.


InterVLAN Routing Using Multilayer Switches

Port roles

• Virtual LAN (VLAN) Port—Acts as layer 2 switching port with a VLAN.

• Static VLAN—Use the switchport command to identify VLAN.

• Dynamic VLAN—Use VLAN Membership Policy Server (VMPS).

• Trunk Port—Passes multiple VLANs and differentiates by tagging.

Use the switchport command to set parameters:

• ISL(Interswitch Link) or 802.1Q

• Switched Virtual Interface (SVI)—Virtual routed port in a VLAN

—Use to route or fallback bridge between VLANs
—Default SVI for VLAN 1 automatically created
—Associate with VLAN using interface vlan#

• Routed port—Acts as layer 3 routed port

—Place in layer 3 mode with no switchport
—Not associated with VLAN
—Turn on routing using ip routing
—Assign address and enable routing protocols as needed


InterVLAN Routing

Multilayer switches do the following:

• Enable IP routing using ip routing

• Create SVI using interface vlan#

• Assign an IP address to each interface

A router on a stick attaches the router to the switch using a trunk line (ISL or 802.1Q). Following are features of these:

• Easy to implement

• Use existing equipment

• Much more latency than Multi-layer switching (MLS) solution

• Configure by creating subinterface with interface fastethernet 1/0.7

• Associate the VLAN to the interface with command encapsulation isl 7 or encapsulation dot1q 7

• ISL—No address on main interface

• 802.1Q—Address on main interface for native (untagged) VLAN