subinterface-number identifies the virtual
interface. The router must be able to talk to the switch using
a standardized trunking protocol. This means that both devices
that are connected together must understand each other. In the
example, 802.1q is used. To define the VLAN encapsulation,
enter the encapsulation command in interface
configuration mode. Router(config-if)#encapsulation
dot1q vlan-number The vlan-number identifies
the VLAN for which the subinterface will carry traffic. A VLAN
ID is added to the frame only when the frame is destined for a
nonlocal network. Each VLAN packet carries the VLAN ID within
the packet header. To assign the IP address to the interface,
enter the following command in interface configuration mode.
Router(config-if)#ip address ip-address
subnet-mask The ip-address and subnet-mask
are the 32-bit network address and mask of the specific
interface. In the example, the router has three subinterfaces
configured on Fast Ethernet interface 0/0. These three
interfaces are identified as 0/0.1, 0/0.2, and 0/0.3. All
interfaces are encapsulated for ISL. Interface 0/0.1 is routing
packets for VLAN 1, whereas interface 0/0.2 is routing packets
for VLAN 20 and 0/0.3 is routing packets for VLAN 30. Lab
Activity Lab Exercise: Configuring Inter-VLAN Routing This
lab is to create a basic configuration on a router and test the
routing functionality. Lab Activity e-Lab Activity:
Configuring Inter-VLAN Routing In this lab, the student will
create a basic configuration on a router and test the routing
functionality. Web Links Configuring InterVLAN Routing
http://www.cisco.com/univercd/cc/
td/doc/product/lan/cat5000/rel_5_2/
layer3/routing.htm
Content Summary An understanding of the following
key points should have been achieved: - The origins and
functions of VLAN trunking
- How trunking enables the
implementation of VLANs in a large network
- IEEE
802.1Q
- Cisco ISL
- Configuring and verifying a
VLAN trunk
- Definition of VLAN Trunking Protocol
(VTP)
- Why VTP was developed
- The contents of
VTP messages
- The three VTP modes
- Configuring
and verifying VTP on an IOS-based switch
- Why routing
is necessary for inter-VLAN communication
- The
difference between physical and logical interfaces
- Subinterfaces
- Configuring inter-VLAN routing using
subinterfaces on a router port