Cisco® CCNA Exam Cram Notes : Wireless Architecture and AP modes

VI. Network Access

1. Wireless Architecture and AP modes

Cisco dCloud content include support for wireless clients and devices. Wireless connectivity is provided by Cisco Access Points (APs). Client connectivity to the AP is determined by how the AP is configured.

Access Point Mode of Operation: A Cisco Access Point (AP) is configured to operate in either Lightweight mode or Autonomous mode.

LAP (Lightweight AP Protocol [LWAPP]): A Cisco LAP is part of the Cisco Unified Wireless Network architecture. An LAP is an AP designed to be connected to a wireless LAN controller (WLC). The WLC manages the AP configurations and firmware; therefore, the LAP cannot act independently of a WLC. This mode is sometimes called controller-based. Enterprise Networking and Security content require lightweight mode. On a lightweight AP, the MAC function is divided between the AP hardware and the wireless LAN controller (WLC). Therefore, the architecture is known as split-MAC. LAP forwards data between the wired and wireless LAN, and specifically forwarding data through the WLC using a protocol like Control And Provisioning of Wireless Access Points (CAPWAP)

Split-MAC Architecture: The LAP-WLC division of labor is known as a split-MAC architecture, where the normal MAC operations are pulled apart into two distinct locations. This occurs for every LAP in the network, each one must boot and bind itself to a WLC to support wireless clients. The WLC becomes the central hub that supports a number of LAPs scattered about in the network. The two devices must use a tunneling protocol between them, to carry 802.11-related messages and also client data. Remember that the AP and WLC can be located on the same VLAN or IP subnet, but they do not have to be. Instead, they can be located on two entirely different IP subnets in two different locations.

A Lightweight Access Point (LAP) can work in one of the following modes based on the user requirement.

a. Local: This is default mode of lightweight access point. In local mode lightweight access point acts as if controller and AP are in same location. And it sends all the traffic (control and data) to controller. If we loose connection to controller, access point will dissociate. It offers one or more functioning BSSs on a specific channel.

b. Flex-connect mode:This is a mode where AP join the controller but switch data packet locally. In this mode AP and controller could be or could not be on same site. With Flex connect mode we can have more resiliency as even if we loose connection to controller, AP continues serving the existing associated clients.

c. Sniffer Mode: It is the mode required to take over the air packet captures. In this mode AP listens the communication between nearby client and AP. To capture the traffic AP listens on specific channel. We need to set the AP in sniffer mode.

d. Monitor Mode: AP in this mode is dedicated for scanning the rogue devices all the time. This can only detect wireless rogues devices. In monitor mode AP does not serve the clients.

e. Rogue Mode: This mode is also for detecting the rogue devices on wired network. This AP connects to wired infrastructure using trunk port and listens for all the traffic coming from all VLANs. If there is any MAC address declared as rogue device by another AP than this AP reports it to controller. And it can also trigger the alerts for rogue devices.

Autonomous AP: A Cisco IOS Software-based AP that functions independently of a WLC. This mode is sometimes called standalone. Collaboration and Customer Collaboration content require autonomous mode. The Cisco Meraki APs are autonomous APs that are managed through a centralized platform in the Meraki cloud.

Cloud based Architecture: To help and manage more and more autonomous APs as the wireless network grows you can place an AP management platform such as Cisco Prime infrastructure in a central location within enterprise. A simple approach is a cloud based AP architecture., where the AP management function is pushed out of the enterprise and into the internet cloud. Cisco Meraki is cloud-based and offers centralized management of wireless, switched and security networks built from meraki products. Cisco Meraki APs can be deployed automatically once you register with the Meraki cloud.

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