Specifications

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Cisco 1751 Router Software Configuration Guide
OL-1070-01
Configuring IP Routing over IEEE 802.1Q
IP routing over IEEE 802.1Q extends IP routing capabilities to include support for routing IP frame
types in VLAN configurations using the IEEE 802.1Q encapsulation.
To route IP over IEEE 802.1Q between VLANs, you need to customize the subinterface to create the
environment in which it will be used. Perform these tasks in the order in which they appear:
• Enabling IP Routing
• Defining the VLAN Encapsulation Format
• Assigning IP Address to Network Interface
Enabling IP Routing
IP routing is automatically enabled in the Cisco IOS software for routers. To reenable IP routing if it
has been disabled, use the following command in global configuration mode:
Once you have IP routing enabled on the router, you can customize the characteristics to suit your
environment. If necessary, refer to the IP configuration chapters in the Cisco IOS IP and IP Routing
Configuration Guide for guidelines on configuring IP.
Defining the VLAN Encapsulation Format
To define the encapsulation format as IEEE 802.1Q, use the following commands in interface
configuration mode:
Assigning IP Address to Network Interface
An interface can have one primary IP address. To assign a primary IP address and a network mask to a
network interface, use the following command in interface configuration mode:
A mask identifies the bits that denote the network number in an IP address. When you use the mask to
subnet a network, the mask is then referred to as a subnet mask.
Command Purpose
ip routing
Enables IP routing on the router.
Command Purpose
Step1
interface fastethernet
slot/port.subinterface-number
Specifies the subinterface on which IEEE 802.1Q will be
used.
Step2
encapsulation dot1q vlanid
Defines the encapsulation format as IEEE 802.1Q (dot1q),
and specify the VLAN identifier
Command Purpose
ip address ip-address mask
Sets a primary IP address for an interface.