Configuring Routing Between VLANs with IEEE 802.1Q Encapsulation

Last Updated: December 8, 2011

This chapter describes the required and optional tasks for configuring routing between VLANs with IEEE 802.1Q encapsulation.

Finding Feature Information

Your software release may not support all the features documented in this module. For the latest feature information and caveats, see the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the Feature Information Table at the end of this document.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.

Restrictions for Configuring Routing Between VLANs with IEEE 802.1Q Encapsulation

Shared port adapters (SPAs) on Cisco ASR 1000 Series Aggregation Services Router have a limit of 8,000 TCAM entries, which limits the number of VLANs you can create on a single SPA.

Information About Configuring Routing Between VLANs with IEEE 802.1Q Encapsulation

Configuring Routing Between VLANs with IEEE 802.1Q Encapsulation

The IEEE 802.1Q protocol is used to interconnect multiple switches and routers, and for defining VLAN topologies. The IEEE 802.1Q standard is extremely restrictive to untagged frames. The standard provides only a per-port VLANs solution for untagged frames. For example, assigning untagged frames to VLANs takes into consideration only the port from which they have been received. Each port has a parameter called a permanent virtual identification (Native VLAN) that specifies the VLAN assigned to receive untagged frames.

The main characteristics of IEEE 802.1Q are as follows:

  • Assigns frames to VLANs by filtering.
  • The standard assumes the presence of a single spanning tree and of an explicit tagging scheme with one-level tagging.

How to Configure Routing Between VLANs with IEEE 802.1Q Encapsulation

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 the tasks described in the following sections in the order in which they appear:

Enabling IP Routing

IP routing is automatically enabled in the Cisco IOS XE software for routers. To reenable IP routing if it has been disabled, perform the following steps.

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 XE IP Routing Protocols Configuration Guide , Release 2, for guidelines on configuring IP.

SUMMARY STEPS

1.    enable

2.    configure terminal

3.    ip routing

4.    end


DETAILED STEPS
  Command or Action Purpose
Step 1
enable


Example:

Router> enable

 

Enables privileged EXEC mode.

  • Enter your password if prompted.
 
Step 2
configure terminal


Example:

Router# configure terminal

 

Enters global configuration mode.

 
Step 3
ip routing


Example:

Router(config)# ip routing

 

Enables IP routing on the router.

 
Step 4
end


Example:

Router(config)# exit

 

Exits privileged EXEC mode.

 

Defining the VLAN Encapsulation Format

To define the encapsulation format as IEEE 802.1Q, perform the following steps.

SUMMARY STEPS

1.    enable

2.    configure terminal

3.    interface gigabitethernet card / spaslot / port . subinterface-number

4.    encapsulation dot1q vlanid

5.    end


DETAILED STEPS
  Command or Action Purpose
Step 1
enable


Example:

Router> enable

 

Enables privileged EXEC mode.

  • Enter your password if prompted.
 
Step 2
configure terminal


Example:

Router# configure terminal

 

Enters global configuration mode.

 
Step 3
interface gigabitethernet card / spaslot / port . subinterface-number


Example:

Router(config)# interface gigabitethernet 0/0/0.101

 

Specifies the subinterface on which IEEE 802.1Q will be used, and enters interface configuration mode.

 
Step 4
encapsulation dot1q vlanid


Example:

Router(config-subif)# encapsulation dot1q 101

 

Defines the encapsulation format as IEEE 802.1Q (dot1q), and specifies the VLAN identifier

 
Step 5
end


Example:

Router(config-subif)# end

 

Exits subinterface configuration mode.

 

Assigning an 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, perform the following steps.

SUMMARY STEPS

1.    enable

2.    configure terminal

3.    interface gigabitethernet card / spaslot / port . subinterface-number

4.    ip address ip-address mask

5.    end


DETAILED STEPS
  Command or Action Purpose
Step 1
enable


Example:

Router> enable

 

Enables privileged EXEC mode.

  • Enter your password if prompted.
 
Step 2
configure terminal


Example:

Router# configure terminal

 

Enters global configuration mode.

 
Step 3
interface gigabitethernet card / spaslot / port . subinterface-number


Example:

Router(config)# interface gigabitethernet 0/0/0.101

 

Specifies the subinterface on which IEEE 802.1Q will be used, and enters interface configuration mode.

 
Step 4
ip address ip-address mask


Example:

Router(config-subif)# ip address 10.0.0.0 255.0.0.0

 

Sets a primary IP address for an interface.

  • Enter the primary IP address for an interface.
Note    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.
 
Step 5
end


Example:

Router(config-subif)# end

 

Exits subinterface configuration mode.

 

Monitoring and Maintaining VLAN Subinterfaces

To indicate whether a VLAN is a native VLAN, perform the following steps.

SUMMARY STEPS

1.    enable

2.    show vlans

3.    end


DETAILED STEPS
  Command or Action Purpose
Step 1
enable


Example:

Router> enable

 

Enables privileged EXEC mode.

  • Enter your password if prompted.
 
Step 2
show vlans


Example:

Router# show vlans

 

Displays VLAN information.

 
Step 3
end


Example:

Router# end

 

Exits privileged EXEC mode.

 

Configuration Examples for Configuring Routing Between VLANs with IEEE 802.1Q Encapsulation

Configuring IP Routing over IEEE 802.1Q Example

This configuration example shows IP being routed on VLAN 101:

!
ip routing
!
interface gigabitethernet 4/1/1.101
  encapsulation dot1q 101
  ip addr 10.0.0.0 255.0.0.0
!

Additional References

The following sections provide references related to the Configuring Routing Between VLANs with IEEE 802.1Q Encapsulation feature.

Related Documents

Related Topic

Document Title

LAN Switching commands

Cisco IOS LAN Switching Command Reference

Cisco IOS commands

Cisco IOS Master Commands List, All Releases

Standards

Standard

Title

No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature.

--

MIBs

MIB

MIBs Link

No new or modified MIBs are supported by this feature, and support for existing MIBs has not been modified by this feature.

To locate and download MIBs for selected platforms, Cisco IOS XE software releases, and feature sets, use Cisco MIB Locator found at the following URL:

http://www.cisco.com/go/mibs

RFCs

RFC

Title

No new or modified RFCs are supported by this feature, and support for existing RFCs has not been modified by this feature.

--

Technical Assistance

Description

Link

The Cisco Support and Documentation website provides online resources to download documentation, software, and tools. Use these resources to install and configure the software and to troubleshoot and resolve technical issues with Cisco products and technologies. Access to most tools on the Cisco Support and Documentation website requires a Cisco.com user ID and password.

http://www.cisco.com/cisco/web/support/index.html

Feature Information for Configuring Routing Between VLANs with IEEE 802.1Q Encapsulation

The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.

Table 1 Feature Information for Configuring Routing Between VLANs with IEEE 802.1Q Encapsulation

Feature Name

Releases

Feature Information

Configuring Routing Between VLANs with IEEE 802.1Q Encapsulation

Cisco IOS XE Release 2.1

This feature was introduced on the Cisco ASR 1000 Series Aggregation Services Routers.

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Any Internet Protocol (IP) addresses and phone numbers used in this document are not intended to be actual addresses and phone numbers. Any examples, command display output, network topology diagrams, and other figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses or phone numbers in illustrative content is unintentional and coincidental.

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