Wireless Concepts

In this sample chapter from 31 Days Before your CCNA Exam: A Day-By-Day Review Guide for the CCNA 200-301 Certification Exam, you will learn how to explain the role and function of network components, describe wireless principles, compare Cisco Wireless Architectures and AP modes, and more.

CCNA 200-301 Exam Topics

• Explain the role and function of network components

• Describe wireless principles

• Compare Cisco Wireless Architectures and AP modes

• Describe physical infrastructure connections of WLAN components (AP, WLC, access/trunk ports, LAG)

• Describe AP and WLC management access connections (Telnet, SSH, HTTP, HTTPS, console, TACACS+/Radius)

• Describe wireless security protocols (WPA, WPA2, and WPA3)

Key Topics

Wireless specifications are detailed in the IEEE 802.11 family of standards, including wireless topologies, spectrum allocation, and wireless security. Today we review basic wireless network concepts.

Wireless Standards

The IEEE 802.11 WLAN standards define how radio frequencies (RFs) are used for wireless links. To avoid interference, different channels within an RF can be used.

RF Spectrum

The RF spectrum, shown in Figure 22-1, includes all types of radio communications, including the 2.4-GHz and 5-GHz frequencies used by wireless devices.

Channels

A frequency range is typically called a band of frequencies. For example, a wireless LAN device with a 2.4-GHz antenna can actually use any frequency from 2.4000 to 2.4835 GHz. The 5-GHz band lies between 5.150 and 5.825 GHz.

The bands are further subdivided into frequency channels. Channels become particularly important when the wireless devices in a specific area become saturated. Each channel is known by a channel number and is assigned to a specific frequency. As long as the channels are defined by a national or international standards body, they can be used consistently in all locations. Figure 22-2 and Figure 22-3 show the channel layouts for the 2.4- and 5-GHz bands, respectively.

Notice in Figure 22-3 that the 5-GHz band consists of nonoverlapping channels. Each channel is allocated a frequency range that does not encroach on or overlap the frequencies allocated for any other channel. The same is not true of the 2.4-GHz band in Figure 22-2. The only way to avoid any overlap between adjacent channels is to configure access points (APs) to use only channels 1, 6, and 11.

802.11 Standards

Most of the standards specify that a wireless device must have one antenna to transmit and receive wireless signals on the specified radio frequency (2.4 GHz or 5 GHz). Some of the newer standards that transmit and receive at higher speeds require APs and wireless clients to have multiple antennas using the multiple input, multiple output (MIMO) technology. MIMO uses multiple antennas as both the transmitter and receiver to improve communication performance. Up to four antennas can be supported.

Various implementations of the IEEE 802.11 standard have been developed over the years. Table 22-1 highlights these standards.

Table 22-1 Summary of 802.11 Standards

Wireless Topologies

The 802.11 standard identifies two main wireless topology modes: infrastructure mode and Independent Basic Service Set (IBSS). IBSS is also knows as ad hoc mode. With the ubiquity of wireless networks, mesh topologies are now common.

Infrastructure Mode

With infrastructure mode, wireless clients interconnect via an AP. Figure 22-4 illustrates infrastructure mode terminology. Notice that the configuration of the APs to share the same SSID allows wireless clients to roam between BSAs.

Infrastructure mode terminology includes the following:

• Basic service set (BSS): This consists of a single AP interconnecting all associated wireless clients.

• Basic service area (BSA): This is the area that is bound by the reach of the AP’s signal. The BSA is also called a cell (the gray area in Figure 22-4).

• Basic service set identifier (BSSID): This is the unique, machine-readable identifier for the AP that is in the format of a MAC address and is usually derived from the AP’s wireless MAC address.

• Service set identifier (SSID): This is a human-readable, non-unique identifier used by the AP to advertise its wireless service.

• Distribution system (DS): APs connect to the network infrastructure using the wired DS, such as Ethernet. An AP with a wired connection to the DS is responsible for translating frames between 802.3 Ethernet and 802.11 wireless protocols.

• Extended service set (ESS): When a single BSS provides insufficient coverage, two or more BSSs can be joined through a common DS into an ESS. An ESS is the union of two or more BSSs interconnected by a wired DS. Each ESS is identified by its SSID, and each BSS is identified by its BSSID.

IBSS, or Ad Hoc Mode

In the 802.11 standard, Independent Basic Service Set (IBSS) is defined as two devices connected wirelessly in a peer-to-peer (P2P) manner without the use of an AP. One device takes the role of advertising the wireless network to clients. The IBSS allows two devices to communicate directly without the need for any other wireless devices, as shown in Figure 22-5. IBSSs do not scale well beyond 8 to 10 devices.

Mesh

Having a wired DS connecting all APs is not always practical or necessary. Instead, APs can be configured to connect in mesh mode. In this mode, APs bridge client traffic between each other, as shown in Figure 22-6.

Each AP in the mesh maintains a BSS on one channel used by wireless clients. Then the APs bridge between each other using other channels. The mesh network runs its own dynamic routing protocol to determine the best path to the wired network.

AP Architectures

APs can be networked together in a variety of architectures. The size and scalability of the network determine which architecture is most suited for a given implementation.

Autonomous AP Architecture

An autonomous AP is a self-contained device with both wired and wireless hardware so that it can bridge to the wired VLAN infrastructure wireless clients that belong to SSIDs, as shown in Figure 22-7. Each autonomous AP must be configured with a management IP address so that it can be remotely accessed using Telnet, SSH, or a web interface. Each AP must be individually managed and maintained unless you use a management platform such as Cisco DNA Center.

Cloud-Based AP Architecture

Cloud-based AP management is an alternative to purchasing a management platform. The AP management function is pushed into the Internet cloud. For example, Cisco Meraki is a cloud-based AP management service that allows you to automatically deploy Cisco Meraki APs. These APs can then be managed from the Meraki cloud web interface (dashboard). In Figure 22-8, the same APs shown in Figure 22-7 are now managed in the cloud.

Notice that there are two distinct paths for data traffic and for management traffic, corresponding to the following two functions:

• A control plane: Traffic used to control, configure, manage, and monitor the AP itself

• A data plane: End-user traffic passing through the AP

Lightweight AP Architectures

Wireless LAN controllers (WLCs) use Lightweight Access Point Protocol (LWAPP) to communicate with lightweight APs (LAPs), as shown in Figure 22-9. LAPs are useful in situations where many APs are required in the network. They are “lightweight” because they only perform the 802.11 wireless operation for wireless clients. Each LAP is automatically configured and managed by the WLC.

Notice in Figure 22-9 that the WLC has four ports connected to the switching infrastructure. These four ports are configured as a link aggregation group (LAG) so they can be bundled together. Much like EtherChannel, LAG provides redundancy and load balancing.

CAPWAP Operation

The division of labor between the WLC and LAPs is known as split-MAC architecture. The LAP must interact with wireless clients on some low level, known as the Media Access Control (MAC) layer. These functions must stay with the LAP hardware, closest to the clients. The management functions are not integral to handling frames but are things that should be centrally administered. Therefore, those functions can be moved to a centrally located platform away from the AP. Table 22-2 summarizes MAC functions of the LAP and WLC.

Table 22-2 Split-MAC Functions of the AP and WLC

LWAPP has been replaced with the Control and Provisioning of Wireless Access Points (CAPWAP) tunneling protocol to implement these split-MAC functions. CAPWAP uses two tunnels—one for control and one for data—as shown in Figure 22-10 and described in the list that follows:

• CAPWAP control message tunnel: Carries exchanges that are used to configure the LAP and manage its operation. The control messages are authenticated and encrypted, so the LAP is securely controlled by only the appropriate WLC and then transported over the control tunnel using UDP port 5246.

• CAPWAP data tunnel: Used for packets traveling to and from wireless clients that are associated with the AP. Data packets are transported over the data tunnel using UDP port 5247 but are not encrypted by default. When data encryption is enabled for a LAP, packets are protected with Datagram Transport Layer Security (DTLS).

Wireless Security Protocols

Wireless traffic is inherently different from traffic traveling over a wired infrastructure. Any wireless device operating in the same frequency can hear the frames and potentially read them. Therefore, WLANs need to be secured to allow only authorized users and devices and to prevent eavesdropping and tampering of wireless traffic.

Wireless Authentication Methods

For wireless devices to communicate over a network, they must first associate with the AP. An important part of the 802.11 process is discovering a WLAN and subsequently connecting to it. During this process, transmitted frames can reach any device within range. If the wireless connection is not secured, then others can read the traffic, as shown in Figure 22-11.

The best way to secure a wireless network is to use authentication and encryption systems.

Two types of authentication were introduced with the original 802.11 standard:

• Open system authentication: Should only be used in situations where security is of no concern. The wireless client is responsible for providing security such as by using a virtual private network (VPN) to connect securely.

• Shared key authentication: Provides mechanisms shown in Table 22-3 to authenticate and encrypt data between a wireless client and an AP. However, the password must be pre-shared between the parties to allow connection.

Table 22-3 Shared Key Authentication Methods

WPA and WPA2

Home routers typically have two choices for authentication: WPA and WPA2. WPA2 is the stronger of the two. WPA2 authentication methods included the following:

• Personal: Intended for home or small office networks, users authenticate using a pre-shared key (PSK). Wireless clients authenticate with the wireless router using a pre-shared password. No special authentication server is required.

• Enterprise: Intended for enterprise networks but requires a Remote Authentication Dial-In User Service (RADIUS) authentication server. Although more complicated to set up, it provides additional security. The device must be authenticated by the RADIUS server, and then users must authenticate using the 802.1X standard, which uses Extensible Authentication Protocol (EAP) for authentication.

802.1X/EAP

With open and WEP authentication, wireless clients are authenticated locally at the AP without further intervention. The scenario changes with 802.1X: The client uses open authentication to associate with the AP, and then the client authentication process occurs at a dedicated authentication server. Figure 22-11 shows the three-party 802.1X arrangement, which consists of the following entities:

• Supplicant: The client device that is requesting access.

• Authenticator: The network device that provides access to the network. In Figure 22-11, the AP forwards the supplicant’s message to the WLC.

• Authentication server (AS): The device that permits or denies network access based on a user database and policies (usually a RADIUS server).

WPA3

WPA3 includes four features:

• WPA3-Personal: In WPA2-Personal, threat actors can listen in on the “handshake” between a wireless client and the AP and use brute-force attacks to try to guess the PSK. WPA3-Personal thwarts such attacks by using Simultaneous Authentication of Equals (SAE), a feature specified in the IEEE 802.11-2016. The PSK is never exposed, making it impossible for the threat actor to guess.

• WPA3-Enterprise: WPA3-Enterprise still uses 802.1X/EAP authentication. However, it requires the use of a 192-bit cryptographic suite and eliminates the mixing of security protocols for previous 802.11 standards. WPA3-Enterprise adheres to the Commercial National Security Algorithm (CNSA) suite, which is commonly used in high-security Wi-Fi networks.

• Open networks: Open networks in WPA2 send user traffic in unauthenticated plaintext. In WPA3, open or public Wi-Fi networks still do not use any authentication. However, they do use Opportunistic Wireless Encryption (OWE) to encrypt all wireless traffic.

• IoT onboarding: Although WPA2 included Wi-Fi Protected Setup (WPS) to quickly onboard devices that were not previously configured, WPS is vulnerable to a variety of attacks and is not recommended. Furthermore, IoT devices are typically headless, meaning they have no built-in GUI for configuration and need any easy way to get connected to the wireless network. Device Provisioning Protocol (DPP) was designed to address this need. Each headless device has a hard-coded public key. The key is typically stamped on the outside of the device or its packaging as a Quick Response (QR) code. The network administrator can scan the QR code and quickly onboard the device. Although DPP is not strictly part of the WPA3 standard, it will replace WPS over time.

Wireless Encryption Methods

Encryption is used to protect data. An intruder may be able to captured encrypted data, but he or she would not be able to decipher it in any reasonable amount of time. The following encryption protocols are used with wireless authentication:

• Temporal Key Integrity Protocol (TKIP): TKIP is the encryption method used by WPA. It provides support for legacy WLAN equipment and addresses the original flaws associated with the 802.11 WEP encryption method. It makes use of WEP but encrypts the Layer 2 payload using TKIP and carries out a message integrity check (MIC) in the encrypted packet to ensure that the message has not been altered.

• Advanced Encryption Standard (AES): AES is the encryption method used by WPA2. It is the preferred method because it is a very strong method of encryption. It uses Counter Cipher Mode with Block Chaining Message Authentication Code Protocol (CCMP), which allows destination hosts to recognize if the encrypted and nonencrypted bits have been altered.

• The Galois/Counter Mode Protocol (GCMP): This is a robust authenticated encryption suite that is more secure and more efficient than CCMP. GCMP is used in WPA3.

Table 22-4 summarizes the basic differences between WPA, WPA2, and WPA3. Each successive version is meant to replace prior versions and offer better security features. You should avoid using WPA and use WPA2 instead—at least until WPA3 becomes widely available on wireless client devices, APs, and WLCs.

Table 22-4 Wireless Authentication and Encryption Comparison

Study Resources

For today’s exam topics, refer to the following resources for more study.