Zyxel NBG6515 Router Manual PDF (Setup & Configuration Guide)

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Preamble Type

Preamble is used to signal that data is coming to the receiver. Short and long refer to the length of

the synchronization field in a packet.

Short preamble increases performance as less time sending preamble means more time for sending

data. All IEEE 802.11 compliant wireless adapters support long preamble, but not all support short

preamble.

Use long preamble if you are unsure what preamble mode other wireless devices on the network

support, and to provide more reliable communications in busy wireless networks.

Use short preamble if you are sure all wireless devices on the network support it, and to provide

more efficient communications.

Use the dynamic setting to automatically use short preamble when all wireless devices on the

network support it, otherwise the NBG uses long preamble.

Note: The wireless devices MUST

use the same preamble mode in order to communicate.

Wireless Security Overview

Wireless security is vital to your network to protect wireless communication between wireless

clients, access points and the wired network.

Wireless security methods available on the NBG are data encryption, wireless client authentication,

restricting access by device MAC address and hiding the NBG identity.

The following figure shows the relative effectiveness of these wireless security methods available on

your NBG.

Note: You must enable the same wireless security settings on the NBG and on all wireless

clients that you want to associate with it.

Table 92

Wireless Security Levels

SECURITY

LEVEL

SECURITY TYPE

Least

Secure

Most Secure

Unique SSID (Default)

Unique SSID with Hide SSID Enabled

MAC Address Filtering

WEP Encryption

IEEE802.1x EAP with RADIUS Server Authentication

Wi-Fi Protected Access (WPA)

WPA2

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IEEE 802.1x

In June 2001, the IEEE 802.1x standard was designed to extend the features of IEEE 802.11 to

support extended authentication as well as providing additional accounting and control features. It

is supported by Windows XP and a number of network devices. Some advantages of IEEE 802.1x

are:

•

User based identification that allows for roaming.

•

Support for RADIUS (Remote Authentication Dial In User Service, RFC 2138, 2139) for

centralized user profile and accounting management on a network RADIUS server.

•

Support for EAP (Extensible Authentication Protocol, RFC 2486) that allows additional

authentication methods to be deployed with no changes to the access point or the wireless

clients.

RADIUS

RADIUS is based on a client-server model that supports authentication, authorization and

accounting. The access point is the client and the server is the RADIUS server. The RADIUS server

handles the following tasks:

• Authentication

Determines the identity of the users.

• Authorization

Determines the network services available to authenticated users once they are connected to the

network.

• Accounting

Keeps track of the client’s network activity.

RADIUS is a simple package exchange in which your AP acts as a message relay between the

wireless client and the network RADIUS server.

Types of RADIUS Messages

The following types of RADIUS messages are exchanged between the access point and the RADIUS

server for user authentication:

• Access-Request

Sent by an access point requesting authentication.

• Access-Reject

Sent by a RADIUS server rejecting access.

• Access-Accept

Sent by a RADIUS server allowing access.

• Access-Challenge

Sent by a RADIUS server requesting more information in order to allow access. The access point

sends a proper response from the user and then sends another Access-Request message.

The following types of RADIUS messages are exchanged between the access point and the RADIUS

server for user accounting:

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• Accounting-Request

Sent by the access point requesting accounting.

• Accounting-Response

Sent by the RADIUS server to indicate that it has started or stopped accounting.

In order to ensure network security, the access point and the RADIUS server use a shared secret

key, which is a password, they both know. The key is not sent over the network. In addition to the

shared key, password information exchanged is also encrypted to protect the network from

unauthorized access.

Types of EAP Authentication

This section discusses some popular authentication types: EAP-MD5, EAP-TLS, EAP-TTLS, PEAP and

LEAP. Your wireless LAN device may not support all authentication types.

EAP (Extensible Authentication Protocol) is an authentication protocol that runs on top of the IEEE

802.1x transport mechanism in order to support multiple types of user authentication. By using EAP

to interact with an EAP-compatible RADIUS server, an access point helps a wireless station and a

RADIUS server perform authentication.

The type of authentication you use depends on the RADIUS server and an intermediary AP(s) that

supports IEEE 802.1x. .

For EAP-TLS authentication type, you must first have a wired connection to the network and obtain

the certificate(s) from a certificate authority (CA). A certificate (also called digital IDs) can be used

to authenticate users and a CA issues certificates and guarantees the identity of each certificate

owner.

EAP-MD5 (Message-Digest Algorithm 5)

MD5 authentication is the simplest one-way authentication method. The authentication server

sends a challenge to the wireless client. The wireless client ‘proves’ that it knows the password by

encrypting the password with the challenge and sends back the information. Password is not sent in

plain text.

However, MD5 authentication has some weaknesses. Since the authentication server needs to get

the plaintext passwords, the passwords must be stored. Thus someone other than the

authentication server may access the password file. In addition, it is possible to impersonate an

authentication server as MD5 authentication method does not perform mutual authentication.

Finally, MD5 authentication method does not support data encryption with dynamic session key. You

must configure WEP encryption keys for data encryption.

EAP-TLS (Transport Layer Security)

With EAP-TLS, digital certifications are needed by both the server and the wireless clients for

mutual authentication. The server presents a certificate to the client. After validating the identity of

the server, the client sends a different certificate to the server. The exchange of certificates is done

in the open before a secured tunnel is created. This makes user identity vulnerable to passive

attacks. A digital certificate is an electronic ID card that authenticates the sender’s identity.

However, to implement EAP-TLS, you need a Certificate Authority (CA) to handle certificates, which

imposes a management overhead.

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EAP-TTLS (Tunneled Transport Layer Service)

EAP-TTLS is an extension of the EAP-TLS authentication that uses certificates for only the server-

side authentications to establish a secure connection. Client authentication is then done by sending

username and password through the secure connection, thus client identity is protected. For client

authentication, EAP-TTLS supports EAP methods and legacy authentication methods such as PAP,

CHAP, MS-CHAP and MS-CHAP v2.

PEAP (Protected EAP)

Like EAP-TTLS, server-side certificate authentication is used to establish a secure connection, then

use simple username and password methods through the secured connection to authenticate the

clients, thus hiding client identity. However, PEAP only supports EAP methods, such as EAP-MD5,

EAP-MSCHAPv2 and EAP-GTC (EAP-Generic Token Card), for client authentication. EAP-GTC is

implemented only by Cisco.

LEAP

LEAP (Lightweight Extensible Authentication Protocol) is a Cisco implementation of IEEE 802.1x.

Dynamic WEP Key Exchange

The AP maps a unique key that is generated with the RADIUS server. This key expires when the

wireless connection times out, disconnects or reauthentication times out. A new WEP key is

generated each time reauthentication is performed.

If this feature is enabled, it is not necessary to configure a default encryption key in the wireless

security configuration screen. You may still configure and store keys, but they will not be used while

dynamic WEP is enabled.

Note: EAP-MD5 cannot be used with Dynamic WEP Key Exchange

For added security, certificate-based authentications (EAP-TLS, EAP-TTLS and PEAP) use dynamic

keys for data encryption. They are often deployed in corporate environments, but for public

deployment, a simple user name and password pair is more practical. The following table is a

comparison of the features of authentication types.

Table 93

Comparison of EAP Authentication Types

EAP-MD5

EAP-TLS

EAP-TTLS

PEAP

LEAP

Mutual Authentication

Yes

Certificate – Client

Yes

Optional

Certificate – Server

Yes

Dynamic Key Exchange

Yes

Credential Integrity

None

Strong

Moderate

Deployment Difficulty

Easy

Hard

Moderate

Client Identity Protection

Yes

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WPA and WPA2

Wi-Fi Protected Access (WPA) is a subset of the IEEE 802.11i standard. WPA2 (IEEE 802.11i) is a

wireless security standard that defines stronger encryption, authentication and key management

than WPA.

Key differences between WPA or WPA2 and WEP are improved data encryption and user

authentication.

If both an AP and the wireless clients support WPA2 and you have an external RADIUS server, use

WPA2 for stronger data encryption. If you don't have an external RADIUS server, you should use

WPA2-PSK (WPA2-Pre-Shared Key) that only requires a single (identical) password entered into

each access point, wireless gateway and wireless client. As long as the passwords match, a wireless

client will be granted access to a WLAN.

If the AP or the wireless clients do not support WPA2, just use WPA or WPA-PSK depending on

whether you have an external RADIUS server or not.

Select WEP only when the AP and/or wireless clients do not support WPA or WPA2. WEP is less

secure than WPA or WPA2.

Encryption

WPA improves data encryption by using Temporal Key Integrity Protocol (TKIP), Message Integrity

Check (MIC) and IEEE 802.1x. WPA2 also uses TKIP when required for compatibility reasons, but

offers stronger encryption than TKIP with Advanced Encryption Standard (AES) in the Counter

mode with Cipher block chaining Message authentication code Protocol (CCMP).

TKIP uses 128-bit keys that are dynamically generated and distributed by the authentication server.

AES (Advanced Encryption Standard) is a block cipher that uses a 256-bit mathematical algorithm

called Rijndael. They both include a per-packet key mixing function, a Message Integrity Check

(MIC) named Michael, an extended initialization vector (IV) with sequencing rules, and a re-keying

mechanism.

WPA and WPA2 regularly change and rotate the encryption keys so that the same encryption key is

never used twice.

The RADIUS server distributes a Pairwise Master Key (PMK) key to the AP that then sets up a key

hierarchy and management system, using the PMK to dynamically generate unique data encryption

keys to encrypt every data packet that is wirelessly communicated between the AP and the wireless

clients. This all happens in the background automatically.

The Message Integrity Check (MIC) is designed to prevent an attacker from capturing data packets,

altering them and resending them. The MIC provides a strong mathematical function in which the

receiver and the transmitter each compute and then compare the MIC. If they do not match, it is

assumed that the data has been tampered with and the packet is dropped.

By generating unique data encryption keys for every data packet and by creating an integrity

checking mechanism (MIC), with TKIP and AES it is more difficult to decrypt data on a Wi-Fi

network than WEP and difficult for an intruder to break into the network.

The encryption mechanisms used for WPA(2) and WPA(2)-PSK are the same. The only difference

between the two is that WPA(2)-PSK uses a simple common password, instead of user-specific

credentials. The common-password approach makes WPA(2)-PSK susceptible to brute-force

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