Cisco IOS Software Configuration Guide for Cisco Aironet Access Points, 12.4(3g)JA & 12.3(8)JEB
Chapter 14 - Configuring VLANs
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Configuring VLANs

Table Of Contents

Configuring VLANs

Understanding VLANs

Related Documents

Incorporating Wireless Devices into VLANs

Configuring VLANs

Configuring a VLAN

Using a RADIUS Server to Assign Users to VLANs

Using a RADIUS Server for Dynamic Mobility Group Assignment

Viewing VLANs Configured on the Access Point

VLAN Configuration Example


Configuring VLANs


This chapter describes how to configure your access point to operate with the VLANs set up on your wired LAN

Understanding VLANs

Configuring VLANs

VLAN Configuration Example

Understanding VLANs

A VLAN is a switched network that is logically segmented, by functions, project teams, or applications rather than on a physical or geographical basis. For example, all workstations and servers used by a particular workgroup team can be connected to the same VLAN, regardless of their physical connections to the network or the fact that they might be intermingled with other teams. You use VLANs to reconfigure the network through software rather than physically unplugging and moving devices or wires.

A VLAN can be thought of as a broadcast domain that exists within a defined set of switches. A VLAN consists of a number of end systems, either hosts or network equipment (such as bridges and routers), connected by a single bridging domain. The bridging domain is supported on various pieces of network equipment such as LAN switches that operate bridging protocols between them with a separate group for each VLAN.

VLANs provide the segmentation services traditionally provided by routers in LAN configurations. VLANs address scalability, security, and network management. You should consider several key issues when designing and building switched LAN networks:

LAN segmentation

Security

Broadcast control

Performance

Network management

Communication between VLANs

You extend VLANs into a wireless LAN by adding IEEE 802.11Q tag awareness to the access point. Frames destined for different VLANs are transmitted by the access point wirelessly on different SSIDs with different WEP keys. Only the clients associated with that VLAN receive those packets. Conversely, packets coming from a client associated with a certain VLAN are 802.11Q tagged before they are forwarded onto the wired network.

If 802.1q is configured on the FastEthernet interface of an access point, the access point always sends keepalives on VLAN1 even if VLAN 1 is not defined on the access point. As a result, the Ethernet switch connects to the access point and generates a warning message. There is no loss of function on both the access point and the switch. However, the switch log contains meaningless messages that may cause more important messages to be wrapped and not be seen.

This behavior creates a problem when all SSIDs on an access point are associated to mobility networks. If all SSIDs are associated to mobility networks, the Ethernet switch port the access point is connected to can be configured as an access port. The access port is normally assigned to the native VLAN of the access point, which is not necessarily VLAN1, which causes the Ethernet switch to generate warning messages saying that traffic with an 802.1q tag is sent from the access point.

You can eliminate the excessive messages on the switch by disabling the keepalive function.

Figure 14-1 shows the difference between traditional physical LAN segmentation and logical VLAN segmentation with wireless devices connected.

Figure 14-1 LAN and VLAN Segmentation with Wireless Devices

Related Documents

These documents provide more detailed information pertaining to VLAN design and configuration:

Cisco IOS Switching Services Configuration Guide. Click this link to browse to this document:
http://www.cisco.com/en/US/docs/ios/12_2/switch/configuration/guide/fswtch_c.html

Cisco Internetwork Design Guide. Click this link to browse to this document:
http://www.cisco.com/en/US/docs/internetworking/design/guide/idg4.html

Cisco Internetworking Technology Handbook. Click this link to browse to this document:
http://www.cisco.com/en/US/docs/internetworking/technology/handbook/ito_doc.html

Cisco Internetworking Troubleshooting Guide. Click this link to browse to this document:
http://www.cisco.com/en/US/docs/internetworking/troubleshooting/guide/tr1901.html

Incorporating Wireless Devices into VLANs

The basic wireless components of a VLAN consist of an access point and a client associated to it using wireless technology. The access point is physically connected through a trunk port to the network VLAN switch on which the VLAN is configured. The physical connection to the VLAN switch is through the access point Ethernet port.

In fundamental terms, the key to configuring an access point to connect to a specific VLAN is to configure its SSID to recognize that VLAN. Because VLANs are identified by a VLAN ID, it follows that if the SSID on an access point is configured to recognize a specific VLAN ID, a connection to the VLAN is established. When this connection is made, associated wireless client devices having the same SSID can access the VLAN through the access point. The VLAN processes data to and from the clients the same way that it processes data to and from wired connections. You can configure up to 16 SSIDs on your access point, so you can support up to 16 VLANs. You can assign only one SSID to a VLAN.

You can use the VLAN feature to deploy wireless devices with greater efficiency and flexibility. For example, one access point can now handle the specific requirements of multiple users having widely varied network access and permissions. Without VLAN capability, multiple access points would have to be employed to serve classes of users based on the access and permissions they were assigned.

These are two common strategies for deploying wireless VLANs:

Segmentation by user groups: You can segment your wireless LAN user community and enforce a different security policy for each user group. For example, you can create three wired and wireless VLANs in an enterprise environment for full-time and part-time employees and also provide guest access.

Segmentation by device types: You can segment your wireless LAN to allow different devices with different security capabilities to join the network. For example, some wireless users might have handheld devices that support only static WEP, and some wireless users might have more sophisticated devices using dynamic WEP. You can group and isolate these devices into separate VLANs.

Configuring VLANs

These sections describe how to configure VLANs on your access point:

Configuring a VLAN

Using a RADIUS Server to Assign Users to VLANs

Viewing VLANs Configured on the Access Point

Configuring a VLAN


Note When you configure VLANs on access points, the Native VLAN must be VLAN1. In a single architecture, client traffic received by the access point is tunneled through an IP-GRE tunnel, which is established on the access point's Ethernet interface native VLAN. Because of the IP-GRE tunnel, some users may configure another switch port as VLAN1. This misconfiguration causes errors on the switch port.


Configuring your access point to support VLANs is a three-step process:

1. Enable the VLAN on the radio and Ethernet ports.

2. Assign SSIDs to VLANs.

3. Assign authentication settings to SSIDs.

This section describes how to assign SSIDs to VLANs and how to enable a VLAN on the access point radio and Ethernet ports. For detailed instructions on assigning authentication types to SSIDs, see Chapter 11 "Configuring Authentication Types." For instructions on assigning other settings to SSIDs, see Chapter 7 "Configuring Multiple SSIDs."

You can configure up to 16 SSIDs on the access point, so you can support up to 16 VLANs that are configured on your LAN.

Beginning in privileged EXEC mode, follow these steps to assign an SSID to a VLAN and enable the VLAN on the access point radio and Ethernet ports:

 
Command
Purpose

Step 1 

configure terminal

Enter global configuration mode.

Step 2 

interface dot11radio

Enter interface configuration mode for the radio interface.

Step 3 

ssid ssid-string

Create an SSID and enter SSID configuration mode for the new SSID. The SSID can consist of up to 32 alphanumeric characters. SSIDs are case sensitive.

The SSID can consist of up to 32 alphanumeric, case-sensitive, characters.

The first character can not contain the following characters:

Exclamation point (!)

Pound sign (#)

Semicolon (;)

The following characters are invalid and cannot be used in an SSID:

Plus sign (+)

Right bracket (])

Front slash (/)

Quotation mark (")

Tab

Trailing spaces

Note You use the ssid command authentication options to configure an authentication type for each SSID. See Chapter 11 "Configuring Authentication Types," for instructions on configuring authentication types.

Step 4 

vlan vlan-id

(Optional) Assign the SSID to a VLAN on your network. Client devices that associate using the SSID are grouped into this VLAN. Enter a VLAN ID from 1 to 4095. You can assign only one SSID to a VLAN.

Tip

Step 5 

exit

Return to interface configuration mode for the radio interface.

Step 6 

interface dot11radio

Enter interface configuration mode for the radio VLAN sub interface.

Step 7 

encapsulation dot1q vlan-id [native]

Enable a VLAN on the radio interface.

(Optional) Designate the VLAN as the native VLAN. On many networks, the native VLAN is VLAN 1.

Step 8 

exit

Return to global configuration mode.

Step 9 

interface fastEthernet0.x

Enter interface configuration mode for the Ethernet VLAN subinterface.

Step 10 

encapsulation dot1q vlan-id [native]

Enable a VLAN on the Ethernet interface.

(Optional) Designate the VLAN as the native VLAN. On many networks, the native VLAN is VLAN 1.

Step 11 

end

Return to privileged EXEC mode.

Step 12 

copy running-config startup-config

(Optional) Save your entries in the configuration file.

This example shows how to:

Name an SSID

Assign the SSID to a VLAN

Enable the VLAN on the radio and Ethernet ports as the native VLAN

# configure terminal
(config)# interface dot11radio0
(config-if)# ssid batman
(config-ssid)# vlan 1
(config-ssid)# exit
(config)# interface dot11radio0.1
(config-subif)# encapsulation dot1q 1 native
(config-subif)# exit
(config)# interface fastEthernet0.1
(config-subif)# encapsulation dot1q 1 native
(config-subif)# exit
(config)# end
 
   

Using a RADIUS Server to Assign Users to VLANs

You can configure your RADIUS authentication server to assign users or groups of users to a specific VLAN when they authenticate to the network.


Note Unicast and multicast cipher suites advertised in WPA information element (and negotiated during 802.11 association) may potentially mismatch with the cipher suite supported in an explicitly assigned VLAN. If the RADIUS server assigns a new vlan ID which uses a different cipher suite from the previously negotiated cipher suite, there is no way for the access point and client to switch back to the new cipher suite. Currently, the WPA and CCKM protocols do not allow the cipher suite to be changed after the initial 802.11 cipher negotiation phase. In this scenario, the client device is disassociated from the wireless LAN.


The VLAN-mapping process consists of these steps:

1. A client device associates to the access point using any SSID configured on the access point.

2. The client begins RADIUS authentication.

3. When the client authenticates successfully, the RADIUS server maps the client to a specific VLAN, regardless of the VLAN mapping defined for the SSID the client is using on the access point. If the server does not return any VLAN attribute for the client, the client is assigned to the VLAN specified by the SSID mapped locally on the access point.

These are the RADIUS user attributes used for vlan-id assignment. Each attribute must have a common tag value between 1 and 31 to identify the grouped relationship.

IETF 64 (Tunnel Type): Set this attribute to VLAN

IETF 65 (Tunnel Medium Type): Set this attribute to 802

IETF 81 (Tunnel Private Group ID): Set this attribute to vlan-id

Using a RADIUS Server for Dynamic Mobility Group Assignment

You can configure a RADIUS server to dynamically assign mobility groups to users or user groups. This eliminates the need to configure multiple SSIDs on the access point. Instead, you need to configure only one SSID per access point.

When users associate to the SSID, the access point passes their login information to WLSM, which passes the information to the RADIUS server. Based on the login information, the RADIUS server assigns the users to the appropriate mobility group and sends their credentials back.

To enable dynamic mobility group assignment, you need to configure the following attributes on the RADIUS server:

Tunnel-Type (64)

Tunnel-Medium-Type(65)

Tunnel-Private-Group-ID (81)

Figure 14-2 Dynamic Mobility Group Assignment

Viewing VLANs Configured on the Access Point

In privileged EXEC mode, use the show vlan command to view the VLANs that the access point supports. This is sample output from a show vlan command:

Virtual LAN ID:  1 (IEEE 802.1Q Encapsulation)
 
   
   vLAN Trunk Interfaces:  Dot11Radio0
FastEthernet0
Virtual-Dot11Radio0
 
   
 This is configured as native Vlan for the following interface(s) :
Dot11Radio0
FastEthernet0
Virtual-Dot11Radio0
 
   
   Protocols Configured:   Address:              Received:        Transmitted:
        Bridging        Bridge Group 1             201688                   0
        Bridging        Bridge Group 1             201688                   0
        Bridging        Bridge Group 1             201688                   0
 
   
Virtual LAN ID:  2 (IEEE 802.1Q Encapsulation)
 
   
   vLAN Trunk Interfaces:  Dot11Radio0.2
FastEthernet0.2
Virtual-Dot11Radio0.2
 
   
   Protocols Configured:   Address:              Received:        Transmitted:
 
   

VLAN Configuration Example

This example shows how to use VLANs to manage wireless devices on a college campus. In this example, three levels of access are available through VLANs configured on the wired network:

Management access—Highest level of access; users can access all internal drives and files, departmental databases, top-level financial information, and other sensitive information. Management users are required to authenticate using Cisco LEAP.

Faculty access—Medium level of access; users can access school Intranet and Internet, access internal files, access student databases, and view internal information such as human resources, payroll, and other faculty-related material. Faculty users are required to authenticate using Cisco LEAP.

Student access—Lowest level of access; users can access school Intranet and the Internet, obtain class schedules, view grades, make appointments, and perform other student-related activities. Students are allowed to join the network using static WEP.

In this scenario, a minimum of three VLAN connections are required, one for each level of access. Because the access point can handle up to 16 SSIDs, you can use the basic design shown in Table 14-1.

Table 14-1 Access Level SSID and VLAN Assignment 

Level of Access
SSID
VLAN ID

Management

boss

01

Faculty

teach

02

Student

learn

03


Managers configure their wireless client adapters to use SSID boss, faculty members configure their clients to use SSID teach, and students configure their wireless client adapters to use SSID learn. When these clients associate to the access point, they automatically belong to the correct VLAN.

You would complete these steps to support the VLANs in this example:

1. Configure or confirm the configuration of these VLANs on one of the switches on your LAN.

2. On the access point, assign an SSID to each VLAN.

3. Assign authentication types to each SSID.

4. Configure VLAN 1, the Management VLAN, on both the fastEthernet and dot11radio interfaces on the access point. You should make this VLAN the native VLAN.

5. Configure VLANs 2 and 3 on both the fastEthernet and dot11radio interfaces on the access point.

6. Configure the client devices.

Table 14-2 shows the commands needed to configure the three VLANs in this example.

Table 14-2 Configuration Commands for VLAN Example 

Configuring VLAN 1
Configuring VLAN 2
Configuring VLAN 3
# configure terminal
(config)# interface dot11radio 
0
(config-if)# ssid boss
(config-ssid)# vlan 01
(config-ssid)# end
# configure terminal
(config)# interface dot11radio 0
(config-if)# ssid teach
(config-ssid)# vlan 02
(config-ssid)# end
# configure terminal
(config)# interface dot11radio 0
(config-if)# ssid learn
(config-ssid)# vlan 03
(config-ssid)# end
 configure terminal
(config) interface 
FastEthernet0.1
(config-subif) encapsulation 
dot1Q 1 native
(config-subif) exit
(config) interface FastEthernet0.2
(config-subif) encapsulation dot1Q 2
(config-subif) bridge-group 2
(config-subif) exit
(config) interface FastEthernet0.3
(config-subif) encapsulation dot1Q 3
(config-subif) bridge-group 3
(config-subif) exit
(config)# interface Dot11Radio 
0.1
(config-subif)# encapsulation 
dot1Q 1 native
(config-subif)# exit
 
        

Note You do not need to configure a bridge group on the subinterface that you set up as the native VLAN. This bridge group is moved to the native subinterface automatically to maintain the link to BVI 1, which represents both the radio and Ethernet interfaces.

(config) interface Dot11Radio 0.2
(config-subif) encapsulation dot1Q 2 
(config-subif) bridge-group 2
(config-subif) exit
(config) interface Dot11Radio 0.3
(config-subif) encapsulation dot1Q 3 
(config-subif) bridge-group 3
(config-subif) exit

Table 14-3 shows the results of the configuration commands in Table 14-2. Use the show running command to display the running configuration on the access point.

Table 14-3 Results of Example Configuration Commands 

VLAN 1 Interfaces
VLAN 2 Interfaces
VLAN 3 Interfaces
interface Dot11Radio0.1
encapsulation dot1Q 1 native
no ip route-cache
no cdp enable
bridge-group 1
bridge-group 1 
subscriber-loop-control
bridge-group 1 
block-unknown-source
no bridge-group 1 source-learning
no bridge-group 1 unicast-flooding
bridge-group 1 spanning-disabled
interface Dot11Radio0.2
encapsulation dot1Q 2
no ip route-cache
no cdp enable
bridge-group 2
bridge-group 2 
subscriber-loop-control
bridge-group 2 
block-unknown-source
no bridge-group 2 source-learning
no bridge-group 2 unicast-flooding
bridge-group 2 spanning-disabled
interface Dot11Radio0.3
encapsulation dot1Q 3
no ip route-cache
bridge-group 3
bridge-group 3 
subscriber-loop-control
bridge-group 3 block-unknown-source
no bridge-group 3 source-learning
no bridge-group 3 unicast-flooding
bridge-group 3 spanning-disabled
interface FastEthernet0.1
encapsulation dot1Q 1 native
no ip route-cache
bridge-group 1
no bridge-group 1 source-learning
bridge-group 1 spanning-disabled
interface FastEthernet0.2
encapsulation dot1Q 2
no ip route-cache
bridge-group 2
no bridge-group 2 source-learning
bridge-group 2 spanning-disabled
interface FastEthernet0.3
encapsulation dot1Q 3
no ip route-cache
bridge-group 3
no bridge-group 3 source-learning
bridge-group 3 spanning-disabled

Notice that when you configure a bridge group on the radio interface, these commands are set automatically:

bridge-group 2 subscriber-loop-control
bridge-group 2 block-unknown-source
no bridge-group 2 source-learning
no bridge-group 2 unicast-flooding
bridge-group 2 spanning-disabled
 
   

When you configure a bridge group on the FastEthernet interface, these commands are set automatically:

no bridge-group 2 source-learning
bridge-group 2 spanning-disabled