InterVLAN Routing

Overview VLANs control broadcast domain size and keep local traffic local.

Key components of InterVLAN Routing Requirements for InterVLAN Routing VLAN capable switch Router: External or integrated within a switch Router to VLAN connection

External Routers Router-on-a-Stick Trunk Link Advantages: –Saves router and switch ports…saves money and reduces complexity. –Scales to larger number of VLANs than one-link-per- VLAN design. Trunk Link Disadvantages: –Additional router overhead –Older IOS versions support limited sets of features on trunked interfaces and may only support ISL trunking encapsulation.

Cisco Layer 3 Feature Cards Catalyst 6000 Family Multilayer Switch Feature Card (MSFC2) Router-on-a-stick most appropriate when other options not available. Route switch processors generally adequate unless a high proportion of traffic crosses VLAN boundaries or a large number of gigabit or greater interfaces are present. Switch Fabric Module adds switching capacity.

Configuring InterVLAN Routing (1) First task to turn on switch routing functionality. –Switch(config)# ip routing Switch virtual interface (most common). –Switch#interface vlan 40 –Switch(config-if)# ip address Routed port (turns an Ethernet switch into an Ethernet Router by turning off a switch port functionality). –Switch(config)# interface fa 0/1 –Switch(config-if)# no switchport –Switch(config-if)# ip address The switch port can now be used as a physical router port for connection to an external device such as a router.

Configuring InterVLAN Routing (2) RSP(config)#ip routing RSP(config)# interface fa 0/1 RSP(config-if)# no switchport RSP(config)-if# ip address Ext(config)# interface fa0/0 Ext(config-if)# ip address InterVLAN routing most likely achieved through a virtual interface. As an example, VLAN 10 and VLAN 20 configured on the multi-layer switch. RSP(config)# interface vlan 10 RSP(config-if)# ip address RSP(config)# interface vlan 20 RSP(config-if)# ip address Don’t forget to enable a routing protocol on both the RSP and External router.

Configuring InterVLAN Routing (3)

Verifying InterVLAN Routing Configurations Switch# show ip route Switch# show ip interface brief Switch# show ip interface fastethernet module/port –Can show if the port is configured for routing Switch# show ip interface fastethernet module/port switchport –Either switchport information will be displayed or “Switchport: Disabled” will indicate the port is likely configured for routing.