Specifications

CHAPTER 4
InterVLAN Routing
Chapter 4
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 an External Router
A Layer 2 switch can connect to a router to provide reachability between VLANs. This can be done either via separate
physical links for each VLAN or via a trunk link from the switch to the router. A trunk link is most common and this type
of setup is frequently called Router on a Stick.
When using a trunk link you must create separate subinterfaces on the router’s physical interface—one subinterface for
each VLAN plus one for the native VLAN. This can work with any kind of switch and the implementation is straightfor-
ward, but the router becomes a single point of failure for all users, and the trunk link might become congested.
The router’s configuration would look similar to the following:
interface FastEthernet0/1
no ip address
duplex auto
speed auto
!
interface FastEthernet0/1.20
description Voice VLAN
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CCNP SWITCH 642-813 Quick Reference by Denise Donohue