Configuring 802.1Q VLAN Interfaces

A VLAN is a group of devices on one or more LANs that are configured so that they can communicate as if they were attached to the same wire, when in fact they are located on a number of different LAN segments. VLANs are very flexible for user and host management, bandwidth allocation, and resource optimization because they are based on logical grouping instead of physical connections.

The IEEE 802.1Q protocol standard addresses the problem of dividing large networks into smaller parts so broadcast and multicast traffic does not consume more bandwidth than necessary. The standard also helps provide a higher level of security between segments of internal networks.

802.1Q Tagged Frames

The IEEE 802.1Q tag-based VLAN uses an extra tag in the MAC header to identify the VLAN membership of a frame across bridges. This tag is used for VLAN and quality of service (QoS) priority identification. The VLAN ID associates a frame with a specific VLAN and provides the information that switches must process the frame across the network. A tagged frame is four bytes longer than an untagged frame and contains two bytes of Tag Protocol Identifier (TPID) residing within the type and length field of the Ethernet frame and two bytes of Tag Control Information (TCI) which starts after the source address field of the Ethernet frame.

Configuring 802.1Q VLAN Interfaces

A VLAN is a group of devices on one or more LANs that are configured so that they can communicate as if they were attached to the same wire, when in fact they are located on a number of different LAN segments. VLANs are very flexible for user and host management, bandwidth allocation, and resource optimization because they are based on logical grouping instead of physical connections.

The IEEE 802.1Q protocol standard addresses the problem of dividing large networks into smaller parts so broadcast and multicast traffic does not consume more bandwidth than necessary. The standard also helps provide a higher level of security between segments of internal networks.

802.1Q Tagged Frames

The IEEE 802.1Q tag-based VLAN uses an extra tag in the MAC header to identify the VLAN membership of a frame across bridges. This tag is used for VLAN and quality of service (QoS) priority identification. The VLAN ID associates a frame with a specific VLAN and provides the information that switches must process the frame across the network. A tagged frame is four bytes longer than an untagged frame and contains two bytes of Tag Protocol Identifier (TPID) residing within the type and length field of the Ethernet frame and two bytes of Tag Control Information (TCI) which starts after the source address field of the Ethernet frame.

Information About Configuring 802.1Q VLAN Interfaces

To configure 802.1Q VLAN interfaces, you must understand these concepts:

Subinterfaces

Subinterfaces are logical interfaces created on a hardware interface. These software-defined interfaces allow for segregation of traffic into separate logical channels on a single hardware interface as well as allowing for better utilization of the available bandwidth on the physical interface.

Subinterfaces are distinguished from one another by adding an extension on the end of the interface name and designation. For instance, the Ethernet subinterface 23 on the physical interface designated TenGigE 0/0/0/0 would be indicated by TenGigE 0/0/0/0.23.

Before a subinterface is allowed to pass traffic it must have a valid tagging protocol encapsulation and VLAN identifier assigned. All Ethernet subinterfaces always default to the 802.1Q VLAN encapsulation. However, the VLAN identifier must be explicitly defined.

Subinterface MTU

The subinterface maximum transmission unit (MTU) is inherited from the physical interface with an additional four bytes allowed for the 802.1Q VLAN tag. By default subinterface inherits MTU of physical interface if the MTU is not configured. We can have maximum 3 different MTU for a subinterface per NPU. .

EFPs

An Ethernet Flow Point (EFP) is a Metro Ethernet Forum (MEF) term describing abstract router architecture. An EFP is implemented by an Layer 2 subinterface with a VLAN encapsulation. The term EFP is used synonymously with an VLAN tagged L2 subinterface. .

Layer 2 VPN on VLANs

The Layer 2 Virtual Private Network (L2VPN) feature enables Service Providers (SPs) to provide Layer 2 services to geographically disparate customer sites.

The configuration model for configuring VLAN attachment circuits (ACs) is similar to the model used for configuring basic VLANs, where the user first creates a VLAN subinterface, and then configures that VLAN in subinterface configuration mode. To create an AC, you need to include the l2transport keyword in the interface command string to specify that the interface is a Layer 2 interface.

VLAN ACs support these modes of L2VPN operation:

  • Basic Dot1Q AC—The AC covers all frames that are received and sent with a specific VLAN tag.

  • QinQ AC—The AC covers all frames received and sent with a specific outer VLAN tag and a specific inner VLAN tag. QinQ is an extension to Dot1Q that uses a stack of two tags.

Each VLAN on a CE-to-PE link can be configured as a separate L2VPN connection (using either VC type 4 or VC type 5).

How to Configure 802.1Q VLAN Interfaces

This section contains the following procedures:

Configuring 802.1Q VLAN Subinterfaces

This task explains how to configure 802.1Q VLAN subinterfaces. To remove these subinterfaces, see the “Removing an 802.1Q VLAN Subinterface” section.

Procedure

Step 1

configure

Example:


RP/0/RP0/CPU0:router# configure

Enters global configuration mode.

Step 2

interface {TenGigE | FortyGigE | HundredGigE | Bundle-Ether} interface-path-id.subinterface

Example:


RP/0/RP0/CPU0:router(config)# interface TenGigE 0/0/0/4.10

Enters subinterface configuration mode and specifies the interface type, location, and subinterface number.

  • Replace the interface-path-id argument with one of the following instances:

  • Physical Ethernet interface instance, or with an Ethernet bundle instance. Naming notation is rack /slot /module /port , and a slash between values is required as part of the notation.

  • Ethernet bundle instance. Range is from 1 through 65535.

  • Replace the subinterface argument with the subinterface value. Range is from 0 through 2147483647.

  • Naming notation is interface-path-id.subinterface , and a period between arguments is required as part of the notation.

Step 3

encapsulation dot1q

Example:


RP/0/RP0/CPU0:router(config-subif)# encapsulation dot1q 100

Sets the Layer 2 encapsulation of an interface.

Step 4

ipv4 address ip-address mask

Example:


RP/0/RP0/CPU0:router(config-subif)# ipv4 address 178.18.169.23/24

Assigns an IP address and subnet mask to the subinterface.

  • Replace ip-address with the primary IPv4 address for an interface.

  • Replace mask with the mask for the associated IP subnet. The network mask can be specified in either of two ways:

  • The network mask can be a four-part dotted decimal address. For example, 255.0.0.0 indicates that each bit equal to 1 means that the corresponding address bit belongs to the network address.

  • The network mask can be indicated as a slash (/) and number. For example, /8 indicates that the first 8 bits of the mask are ones, and the corresponding bits of the address are network address.

Step 5

exit

Example:


RP/0/RP0/CPU0:router(config-subif)# exit

(Optional) Exits the subinterface configuration mode.

  • The exit command is not explicitly required.

Step 6

Repeat Step 2 through Step 5 to define the rest of the VLAN subinterfaces.

—

Step 7

end or commit

Example:


RP/0/RP0/CPU0:router(config)# end

or 


RP/0/RP0/CPU0:router(config)# commit

Saves configuration changes.

  • When you issue the end command, the system prompts you to commit changes: 

    
Uncommitted changes found, commit them before exiting(yes/no/cancel)?
[cancel]:

    - Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.

    - Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.

    - Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.

  • Use the commit command to save the configuration changes to the running configuration file and remain within the configuration session.

Step 8

show ethernet trunk bundle-ether instance

Example:


RP/0/RP0/CPU0:router# show ethernet trunk bundle-ether 5

(Optional) Displays the interface configuration.

The Ethernet bundle instance range is from 1 through 65535.

Verification

This example shows how to verify the configuration of Ethernet interfaces : 

# show ethernet trunk be 1020 Wed May 17 16:43:32.804 EDT

Trunk                                 Sub types        Sub states  
Interface     St Ly    MTU    Subs       L2      L3       Up    Down  Ad-Down
BE1020       Up L3   9100       3        3       0        3      0        0

Summary                         3        3       0        3      0        0

Configuring an Attachment Circuit on a VLAN

Use the following procedure to configure an attachment circuit on a VLAN.

Procedure

Step 1

configure

Example:


RP/0//CPU0:router# configure

Enters global configuration mode.

Step 2

interface [GigabitEthernet | TenGigE | Bundle-Ether | FortyGigE] interface-path] id.subinterface l2transport

Example:


RP/0//CPU0:router(config)# interface TenGigE 0/0/0/1.1 l2transport

Enters subinterface configuration and specifies the interface type, location, and subinterface number.

  • Replace the interface-path-id argument with one of the following instances:

  • Physical Ethernet interface instance, or with an Ethernet bundle instance. Naming notation is rack /slot /module /port , and a slash between values is required as part of the notation.

  • Ethernet bundle instance. Range is from 1 through 65535.

  • Replace the subinterface argument with the subinterface value. Range is from 0 through 4095.

  • Naming notation is instance.subinterface , and a period between arguments is required as part of the notation.

  • You must include the l2transport keyword in the command string; otherwise, the configuration creates a Layer 3 subinterface rather that an AC.

Step 3

encapsulation dot1q 100

Example:


RP/0//CPU0:router (config-subif)# encapsulation dot1q 100

Sets the Layer 2 encapsulation of an interface.

Note

 

The dot1q vlan command is replaced by the encapsulation dot1q command. It is still available for backward-compatibility, but only for Layer 3 interfaces.

Step 4

end or commit

Example:


RP/0//CPU0:router(config-if-l2)# end

or 


RP/0//CPU0:router(config-if-l2)# commit

Saves configuration changes.

  • When you issue the end command, the system prompts you to commit changes: 

    
Uncommitted changes found, commit them before exiting(yes/no/cancel)?
[cancel]:

    - Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.

    - Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.

    - Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.

  • Use the commit command to save the configuration changes to the running configuration file and remain within the configuration session.

Step 5

show interfaces [GigabitEthernet |FortyGigE|Bundle-Ether | TenGigE] interface-path-id.subinterface

Example:


RP/0//CPU0:router# show interfaces TenGigE 0/0/0/3.1

(Optional) Displays statistics for interfaces on the router.

Removing an 802.1Q VLAN Subinterface

This task explains how to remove 802.1Q VLAN subinterfaces that have been previously configured using the Configuring 802.1Q VLAN subinterfaces section in this module.

Procedure

Step 1

configure

Example:


RP/0/RP0/CPU0:router# configure

Enters global configuration mode.

Step 2

no interface {TenGigE | FortyGigE | HundredGigE | Bundle-Ether] interface-path-id.subinterface

Example:


RP/0/RP0/CPU0:router(config)# no interface TenGigE 0/0/0/4.10

Removes the subinterface, which also automatically deletes all the configuration applied to the subinterface.

  • Replace the instance argument with one of the following instances:

  • Physical Ethernet interface instance, or with an Ethernet bundle instance. Naming notation is rack /slot /module /port , and a slash between values is required as part of the notation.

  • Ethernet bundle instance. Range is from 1 through 65535.

  • Replace the subinterface argument with the subinterface value. Range is from 0 through 2147483647.

Naming notation is instance.subinterface , and a period between arguments is required as part of the notation.

Step 3

Repeat Step 2 to remove other VLAN subinterfaces.

—

Step 4

end or commit

Example:


RP/0/RP0/CPU0:router(config)# end

or 


RP/0/RP0/CPU0:router(config)# commit

Saves configuration changes.

  • When you issue the end command, the system prompts you to commit changes: 

    
Uncommitted changes found, commit them before exiting(yes/no/cancel)?
[cancel]:

    - Entering yes saves configuration changes to the running configuration file, exits the configuration session, and returns the router to EXEC mode.

    - Entering no exits the configuration session and returns the router to EXEC mode without committing the configuration changes.

    - Entering cancel leaves the router in the current configuration session without exiting or committing the configuration changes.

  • Use the commit command to save the configuration changes to the running configuration file and remain within the configuration session.