CCNP Exam Prep Tips and Must Knows about WLANs

Wireless Local Area Networks (WLANs)

• A WLAN is a shared network
• An access point is a shared device that functions like a shared Ethernet hub
• Data is transmitted over radio waves
• Two-way radio communication (half-duplex) is used
• The same radio frequency is used for transmitting and receiving

WLANs vs. LANs

• WLANs use radio waves as the physical layer
  • WLANs transmit data over the air instead of over wires
  • WLANs use CSMA/CA instead of CSMA/CD to access the media
• Radio waves have problems that are not encountered in wires
  • Connectivity issues
  • Coverage problems
  • Multipath issues
  • Interference, noise
• Privacy issues
• WLANs use mobile clients
  • Battery-powered
• WLANs must meet country-specific RF regulations

SSIDs

• An SSID (network name) is used to logically separate WLANs
• APs are configured with SSIDs
• An AP broadcasts the SSID
• An SSID must match on the client and the AP
• A client can be configured with an SSID (hotspot mode)

SSID and VLAN support

• One SSID per VLAN
• SSID mapped to a VLAN, security, and QoS configuration
• 802.1Q trunk on the wired side
• Cisco currently supports 16 SSIDs and 16 VLANs

Client Roaming

• Roaming occurs when a client moves out of a wireless cell and into new wireless cell
• Client initiates roaming when signal strength decreases and error rate increases
• MAC address table of the switches is updated when the client roams into a new AP
• Roaming without interruption requires the same as SSID and security configuration on all APs

Security on the WLANs and LANs

• Data can be encrypted on a wireless link (WLAN)
• Data is unencrypted on unwired link (LAN)
• Open wireless networks allow access in the text to the wired network
• Solutions
  • Implement authentication to control access to the wireless network
  • Encrypt data on the wireless link
  • Implement firewall, IPS, and NAC to secure access to the network
  • Use of VPN encryption on the wired network is required

Stand-Alone WLAN Solution

• ACS: RADIUS or TACACS+ Server
• Cisco WLSE: Centralized management and monitoring
• WDS: Management support for Cisco WLSE
• Network infrastructure: PoE switch and router
• Stand-alone AP
• Traffic between wireless clients flows via switch SSIDs, VLANs, and Trunks
• Mapping SSID, VLAN, and subnet at stand-alone AP
• The client becomes a station within a VLAN connected to the AP
• The client gets an IP address from a VLAN for subnet connected to the AP
• The same VLANs or subnets on all APs
• Layer 2 connection between APs
• Layer 2 roaming only

Controller-Based WLAN Solution

• ACS: RADIUS or TACACS+ Server
• Cisco WCS: Centralized management and monitoring
• Cisco Wireless Location Appliance: Location tracking
• Cisco WLC: AP and WLAN configuration
• Network infrastructure: PoE switch and router
• Controller-based AP
• Traffic between wireless clients flows via Controller

AP MAC Functions

• 802.11: Beacons, probe responses
• 802.11 control: Packet acknowledgement and transmission
• 802.11e: Frame queuing and packet prioritization
• 802.11i: MAC layer data encryption and decryption

Controller MAC Functions

• 802.11: MAC management association requests and actions
• 802.11e: Resource reservation
• 802.11i: Authentication and key management

SSIDs, VLANs, and Trunks

• Mapping of SSID, VLAN, and subnet at the WLAN controller
• The client becomes a station within a VLAN for subnet connected to the WLAN controller
• Any VLAN or subnets can be connected to the APs
• APs and W.LAN controller can be on same or different subnet
• Layer 3 IP connection between APs and WLAN controller
• Layer 2 and layer 3 roaming are supported via WLAN controller

SSIDs, VLANs, and Trunks with the H.-REAP

• AP needs to connect to the WLC
• Some WLANs are Locally Switched
• Some WLANs are centrally switched
• Trunk needs to allow locally switched VLANs
• Native VLAN is the AP VLAN

WLC ports and protocols

• The WLC uses these ports and protocols for communication with APs and management
• These ports and protocols must be allowed in the ACLs and firewall
• Other ports and protocols may be used in future

• CAPWAP: UDP ports 5246, 5247
• LWAPP: UDP ports 12222, 12223
• HTTPS: TCP Port 443
• SSH: TCP Port 22
• RADIUS: UDP ports 1812, 1813
• SNMP: UDP ports 161, 162
• Mobility: UDP ports 16666, 16667, EoIP protocol

AP and Controller Placement

• The APs are connected to access switches
• The WLC is connected to the network
  • Distribution switches
  • Server farm or data center

• Centralized deployment is recommended
• Minimize inter-controller roaming
• Implement deterministic redundancy

Centralized deployment with the integrated platforms

• Catalyst 3750G Integrated Wireless LAN Controller for small to medium deployments
• Catalyst 6500 series WiSM for medium to large deployments
• Distributed deployment can be an alternative for existing networks

Configuration for Stand-Alone AP and H-REAP

• Switch(config)# interface fa 0/1
• Switch(config-if)# switchport encapsulation dot1q
• Switch(config-if)# switchport trunk native vlan 10
• Switch(config-if)# switchport trunk allowed vlan 10, 20
• Switch(config-if)# switchport mode trunk
• Switch(config-if)# spanning-tree portfast trunk
• Switch(config-if)# mls qos trust [cos | dscp]

Configuration for Controller-Based AP

• Switch(config)# interface fa0/2
• Switch(config-if)# switchport access the vlan 10
• Switch(config-if)# switchport mode access
• Switch(config-if)# spanning — tree portfast
• Switch(config-if)# mls qos trust dscp

Configuration for WLAN Controller

• Switch(config)# interface fa 0/3
• Switch(config-if)# switchport encapsulation dot1q
• Switch(config-if)# switchport trunk native vlan 99
• Switch(config-if)# switchport trunk allowed vlan 10, 20
• Switch(config-if)# switchport mode trunk
• Switch(config-if)# spanning-tree portfast trunk
• Switch(config-if)# mls qos trust cos

4400 Series Controller with link aggregation

• One link aggregation group (LAG) for Cisco Wireless LAN Controller
• Packets are forwarded from the controller on the same port on which they arrived
• Load balancing is performed on the switch
• A connection is made to a single switch or stack
• EtherChannel configuration on switch is required

Implementation Plan

• Collect the required
• Check the existing network
• Plan for additional equipment
• Plan the implementation
• Implement the new network components
• Test the implemented network

Test Plan

• Can you reach the AP or WLC from management station
• Can the AP reach the DHCP server
• Does the AP get an IP address
• Can the WLC reach RADIUS server
• Do the clients get an IP address
• Can the client access the network, server, Internet

Make sure you can configure:

• Stand-alone AP and H-REAP
• Controller-based AP
• WLAN controller

Make sure you are familiar with:

• Differences between WLAN and LAN
• Client roaming
• Security on the WLAN and LAN
• Stand-alone WLAN solution
• Controller-based WLAN solution
• AP MAC functions
• Controller MAC function
• WLC ports and protocols
• AP and Controller placement
• H-REAP
• LAG
• WLAN Implementation and test plans