4. Inter-VLAN Routing

4. Inter-VLAN Routing

1. Inter-VLAN Routing Operation

   • Process of forwarding network traffic from one VLAN to another
   • Hosts in a VLAN can communicate only if there's a router, or a layer 3 switch
   • A router's interface is configured using subinterfaces to identify routable VLANs
     • These are software-based virtual interfaces
   • The modern method is Inter-VLAN routing on a Layer 3 switch using SVIs
     • SVI provides Layer 3 processing

2. Router-on-a-stick Inter-VLAN Routing

   • Configure a switch with VLANs and trunking
     • 1. Create and name the VLAN's
     • 2. Create management interface
     • 3. Configure access ports
     • 4. Configure trunking ports
   • This method requires a subinterface to be created for each VLAN to be routed
     • interface (interface id) (subinterface id)
     • After creating all subinterfaces, enable the physical interface
       • no shutdown
   • To verify and trouble shoot
     • ping
     • show ip route
     • show ip interface brief
     • show interfaces
     • show interfaces trunk

3. Inter-VLAN Routing using layer 3 switches

   • Layer 3 switches use hardware-based switching to achieve higher-packet processing rates than routers
   • Layer 3 switches can:
     • route from one VLAN to another suing multiple SVIs
     • convert a layer 2 switchport to a layer 3 interface
   • A Layer 3 SVI must be created for each of the routable VLANs.
   • To configure a switch with VLANS and trunking:
     • 1. Create VLANs
     • 2. Create the SVI VLAN interfaces
     • 3. Configure access ports
     • 4. Enable IP routing
       • To enable routing on a Layer 3 switch, a routed port must be configured.
   • To configure a Layer 3 switch to route with a router
     • 1. Configure the routed port
     • 2. Enable routing
     • 3. Configure routing
     • 4. Verify routing
     • 5. Verify connectivity

4. Troubleshoot Inter-VLAN routing

   • Connectivity common problems
     • missing VLANs
     • switch trunk port issues
     • switch access port issues
     • router configuration issues
   • VLAN common problems
     • it's not created
     • accidentally deleted
     • not allowed on the trunk link
   • Useful commands
     • ping
     • show interfaces (interface id)
     • switchport
     • show interface brief

5. Francisco Vaca Silva