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802.1X Port-Based Authentication HOWTO

Lars Strand

<lars strand (at) gnist org>

Revision History                                                             
Revision 1.0             2004-10-18            Revised by: LKS               
Initial Release, reviewed by TLDP.                                           
Revision 0.2b            2004-10-13            Revised by: LKS               
Various updates. Thanks to Rick Moen <rick (at) linuxmafia com> for language 
Revision 0.0             2004-07-23            Revised by: LKS               
Initial draft.                                                               

  This document describes the software and procedures to set up and use IEEE
802.1X Port-Based Network Access Control using Xsupplicant as Supplicant with
FreeRADIUS as a back-end Authentication Server.

Table of Contents
1. Introduction
    1.1. What is 802.1X?
    1.2. What is 802.11i?
    1.3. What is EAP?
    1.4. EAP authentication methods
    1.5. What is RADIUS?
2. Obtaining Certificates
3. Authentication Server: Setting up FreeRADIUS
    3.1. Installing FreeRADIUS
    3.2. Configuring FreeRADIUS
4. Supplicant: Setting up Xsupplicant
    4.1. Installing Xsupplicant
    4.2. Configuring Xsupplicant
5. Authenticator: Setting up the Authenticator (Access Point)
    5.1. Access Point
    5.2. Linux Authenticator
6. Testbed
    6.1. Testcase
    6.2. Running some tests
7. Note about driver support and Xsupplicant
8. FAQ
9. Useful Resources
10. Copyright, acknowledgments and miscellaneous
    10.1. Copyright and License
    10.2. How this document was produced
    10.3. Feedback
    10.4. Acknowledgments
A. GNU Free Documentation License
    A.12. ADDENDUM: How to use this License for your documents

1. Introduction

  This document describes the software and procedures to set up and use 
802.1X: Port-Based Network Access Control using Xsupplicant with PEAP (PEAP/
MS-CHAPv2) as authentication method and FreeRADIUS as back-end authentication

  If another authentication mechanism than PEAP is preferred, e.g., EAP-TLS
or EAP-TTLS, only a small number of configuration options needs to be
changed. PEAP/MS-CHAPv2 are also supported by Windows XP SP1/Windows 2000

1.1. What is 802.1X?

The 802.1X-2001 standard states:

  "Port-based network access control makes use of the physical access
characteristics of IEEE 802 LAN infrastructures in order to provide a means
of authenticating and authorizing devices attached to a LAN port that has
point-to-point connection characteristics, and of preventing access to that
port in cases which the authentication and authorization fails. A port in
this context is a single point of attachment to the LAN infrastructure." ---
802.1X-2001, page 1.


Figure 802.1X: A wireless node must be authenticated before it can gain
access to other LAN resources.

 1.   When a new wireless node (WN) requests access to a LAN resource, the
    access point (AP) asks for the WN's identity. No other traffic than EAP
    is allowed before the WN is authenticated (the "port" is closed).
      The wireless node that requests authentication is often called 
    Supplicant, although it is more correct to say that the wireless node 
    contains a Supplicant. The Supplicant is responsible for responding to
    Authenticator data that will establish its credentials. The same goes for
    the access point; the Authenticator is not the access point. Rather, the
    access point contains an Authenticator. The Authenticator does not even
    need to be in the access point; it can be an external component.
      EAP, which is the protocol used for authentication, was originally used
    for dial-up PPP. The identity was the username, and either PAP or CHAP
    authentication [[] RFC1994] was used
    to check the user's password. Since the identity is sent in clear (not
    encrypted), a malicious sniffer may learn the user's identity. "Identity
    hiding" is therefore used; the real identity is not sent before the
    encrypted TLS tunnel is up.
 2.   After the identity has been sent, the authentication process begins.
    The protocol used between the Supplicant and the Authenticator is EAP,
    or, more correctly, EAP encapsulation over LAN (EAPOL). The Authenticator
    re-encapsulates the EAP messages to RADIUS format, and passes them to the
    Authentication Server.
      During authentication, the Authenticator just relays packets between
    the Supplicant and the Authentication Server. When the authentication
    process finishes, the Authentication Server sends a success message (or
    failure, if the authentication failed). The Authenticator then opens the 
    "port" for the Supplicant.
 3.   After a successful authentication, the Supplicant is granted access to
    other LAN resources/Internet.

  See figure 802.1X for explanation.

  Why is it called "port"-based authentication? The Authenticator deals with 
controlled and uncontrolled ports. Both the controlled and the uncontrolled
port are logical entities (virtual ports), but use the same physical
connection to the LAN (same point of attachment).


Figure port: The authorization state of the controlled port.

  Before authentication, only the uncontrolled port is "open". The only
traffic allowed is EAPOL; see Authenticator System 1 on figure port. After
the Supplicant has been authenticated, the controlled port is opened, and
access to other LAN resources are granted; see Authenticator System 2 on
figure port.

  802.1X plays a major role in the new IEEE wireless standard 802.11i.

1.2. What is 802.11i?

1.2.1. WEP

  Wired Equivalent Privacy (WEP), which is part of the original 802.11
standard, should provide confidentiality. Unfortunately WEP is poorly
designed and easily cracked. There is no authentication mechanism, only a
weak form of access control (must have the shared key to communicate). Read
more [] here.

  As a response to WEP broken security, IEEE has come up with a new wireless
security standard named 802.11i. 802.1X plays a major role in this new

1.2.2. 802.11i

  The new security standard, 802.11i, which was ratified in June 2004, fixes
all WEP weaknesses. It is divided into three main categories:

 1.   Temporary Key Integrity Protocol (TKIP) is a short-term solution that
    fixes all WEP weaknesses. TKIP can be used with old 802.11 equipment
    (after a driver/firmware upgrade) and provides integrity and
 2.   Counter Mode with CBC-MAC Protocol (CCMP) [[
    rfc3610.txt] RFC2610] is a new protocol, designed from ground up. It uses
    AES [FIPS 197] as its cryptographic algorithm, and, since this is more
    CPU intensive than RC4 (used in WEP and TKIP), new 802.11 hardware may be
    required. Some drivers can implement CCMP in software. CCMP provides
    integrity and confidentiality.
 3.   802.1X Port-Based Network Access Control: Either when using TKIP or
    CCMP, 802.1X is used for authentication.

  In addition, an optional encryption method called "Wireless Robust
Authentication Protocol" (WRAP) may be used instead of CCMP. WRAP was the
original AES-based proposal for 802.11i, but was replaced by CCMP since it
became plagued by property encumbrances. Support for WRAP is optional, but
CCMP support is mandatory in 802.11i.

  802.11i also has an extended key derivation/management, described next.

1.2.3. Key Management Dynamic key exchange and management

  To enforce a security policy using encryption and integrity algorithms,
keys must be obtained. Fortunately, 802.11i implements a key derivation/
management regime. See figure KM.


Figure KM: Key management and distribution in 802.11i.

 1.   When the Supplicant (WN) and Authentication Server (AS) authenticate,
    one of the last messages sent from AS, given that authentication was
    successful, is a Master Key (MK). After it has been sent, the MK is known
    only to the WN and the AS. The MK is bound to this session between the WN
    and the AS.
 2.   Both the WN and the AS derive a new key, called the Pairwise Master Key
    (PMK), from the Master Key.
 3.   The PMK is then moved from the AS to the Authenticator (AP). Only the
    WN and the AS can derive the PMK, else the AP could make access-control
    decisions instead of the AS. The PMK is a fresh symmetric key bound to
    this session between the WN and the AP.
 4.   PMK and a 4-way handshake are used between the WN and the AP to derive,
    bind, and verify a Pairwise Transient Key (PTK). The PTK is a collection
    of operational keys:
    ��+�  Key Confirmation Key (KCK), as the name implies, is used to prove
        the posession of the PMK and to bind the PMK to the AP.
    ��+�  Key Encryption Key (KEK) is used to distributed the Group Transient
        Key (GTK). Described below.
    ��+�  Temporal Key 1 & 2 (TK1/TK2) are used for encryption. Usage of TK1
        and TK2 is ciphersuite-specific.
      See figure PKH for a overview of the Pairwise Key Hierarchy.
 5.   The KEK and a 4-way group handshake are then used to send the Group
    Transient Key (GTK) from the AP to the WN. The GTK is a shared key among
    all Supplicants connected to the same Authenticator, and is used to
    secure multicast/broadcast traffic.


Figure PKH: Pairwise Key Hierarchy
----------------------------------------------------------------------------- Pre-shared Key

  For small office / home office (SOHO), ad-hoc networks or home usage, a
pre-shared key (PSK) may be used. When using PSK, the whole 802.1X
authentication process is elided. This has also been called "WPA Personal"
(WPA-PSK), whereas WPA using EAP (and RADIUS) is "WPA Enterprise" or just 

  The 256-bit PSK is generated from a given password using PBKDFv2 from
[[] RFC2898], and is used as the Master
Key (MK) described in the key management regime above. It can be one single
PSK for the whole network (insecure), or one PSK per Supplicant (more

1.2.4. TSN (WPA) / RSN (WPA2)

  The industry didn't have time to wait until the 802.11i standard was
completed. They wanted the WEP issues fixed now! []
Wi-Fi Alliance felt the pressure, took a "snapshot" of the standard (based on
draft 3), and called it Wi-Fi Protected Access (WPA). One requirement was
that existing 802.11 equipment could be used with WPA, so WPA is basically
TKIP + 802.1X.

  WPA is not the long term solution. To get a Robust Secure Network (RSN),
the hardware must support and use CCMP. RSN is basically CCMP + 802.1X.

  RSN, which uses TKIP instead of CCMP, is also called Transition Security
Network (TSN). RSN may also be called WPA2, so that the market don't get



��*�TSN = TKIP + 802.1X = WPA(1)
��*�RSN = CCMP + 802.1X = WPA2

In addition comes key management, as described in the previous section.

1.3. What is EAP?

  Extensible Authentication Protocol (EAP) [[
rfc3748.txt] RFC 3748] is just the transport protocol optimized for
authentication, not the authentication method itself:

  " [EAP is] an authentication framework which supports multiple
authentication methods. EAP typically runs directly over data link layers
such as Point-to-Point Protocol (PPP) or IEEE 802, without requiring IP. EAP
provides its own support for duplicate elimination and retransmission, but is
reliant on lower layer ordering guarantees. Fragmentation is not supported
within EAP itself; however, individual EAP methods may support this." --- RFC
3748, page 3

1.4. EAP authentication methods

  Since 802.1X is using EAP, multiple different authentication schemes may be
added, including smart cards, Kerberos, public key, one time passwords, and

  Some of the most-used EAP authentication mechanism are listed below. A full
list of registered EAP authentication types is available at IANA: [http://]

Warning Not all authentication mechanisms are considered secure!             

��*�  EAP-MD5: MD5-Challenge requires username/password, and is equivalent to
    the PPP CHAP protocol [[] RFC1994].
    This method does not provide dictionary attack resistance, mutual
    authentication, or key derivation, and has therefore little use in a
    wireless authentication enviroment.
��*�  Lightweight EAP (LEAP): A username/password combination is sent to a
    Authentication Server (RADIUS) for authentication. Leap is a proprietary
    protocol developed by Cisco, and is not considered secure. Cisco is
    phasing out LEAP in favor of PEAP. The closest thing to a published
    standard can be found [
    2001-September/002042.html] here.
��*�  EAP-TLS: Creates a TLS session within EAP, between the Supplicant and
    the Authentication Server. Both the server and the client(s) need a valid
    (x509) certificate, and therefore a PKI. This method provides
    authentication both ways. EAP-TLS is described in [[
    rfc/rfc2716.txt] RFC2716].
��*�  EAP-TTLS: Sets up a encrypted TLS-tunnel for safe transport of
    authentication data. Within the TLS tunnel, (any) other authentication
    methods may be used. Developed by Funk Software and Meetinghouse, and is
    currently an IETF draft.
��*�  Protected EAP (PEAP): Uses, as EAP-TTLS, an encrypted TLS-tunnel.
    Supplicant certificates for both EAP-TTLS and EAP-PEAP are optional, but
    server (AS) certificates are required. Developed by Microsoft, Cisco, and
    RSA Security, and is currently an IETF draft.
��*�  EAP-MSCHAPv2: Requires username/password, and is basically an EAP
    encapsulation of MS-CHAP-v2 [[]
    RFC2759]. Usually used inside of a PEAP-encrypted tunnel. Developed by
    Microsoft, and is currently an IETF draft.

1.5. What is RADIUS?

  Remote Authentication Dial-In User Service (RADIUS) is defined in [[http://] RFC2865] (with friends), and was primarily used
by ISPs who authenticated username and password before the user got
authorized to use the ISP's network.

  802.1X does not specify what kind of back-end authentication server must be
present, but RADIUS is the "de-facto" back-end authentication server used in

  There are not many AAA protocols available, but both RADIUS and DIAMETER
[[] RFC3588] (including their extensions)
conform to full AAA support. AAA stands for Authentication, Authorization,
and Accounting (IETF's AAA Working Group).

2. Obtaining Certificates

Note OpenSSL must be installed to use either EAP-TLS, EAP-TTLS, or PEAP!     

  When using EAP-TLS, both the Authentication Server and all the Supplicants
(clients) need certificates [[] RFC2459] .
Using EAP-TTLS or PEAP, only the Authentication Server requires certificates;
Supplicant certificates are optional.

  You get certificates from the local certificate authority (CA). If there is
no local CA available, OpenSSL may be used to generate self-signed

  Included with the FreeRADIUS source are some helper scripts to generate
self-signed certificates. The scripts are located under the scripts/ folder
included with the FreeRADIUS source:

  CA.all is a shell script that generates certificates based on some
questions it ask. CA.certs generates certificates non-interactively based on
pre-defined information at the start of the script.

Note The scripts uses a Perl script called, included with OpenSSL. The 
     path to this Perl script in CA.all and CA.certs may need to be changed  
     to make it work.                                                        

Tip More information on how to generate your own certificates can be found in
    the SSL certificates HOWTO.                                              

3. Authentication Server: Setting up FreeRADIUS

  FreeRADIUS is a fully GPLed RADIUS server implementation. It supports a
wide range of authentication mechanisms, but PEAP is used for the example in
this document.

3.1. Installing FreeRADIUS

Installing FreeRADIUS

 1.   Head over to the FreeRADIUS site, [] http://, and download the latest release.
       # cd /usr/local/src                                                   
       # wget    
       # tar zxfv freeradius-1.0.0.tar.gz                                    
       # cd freeradius-1.0.0                                                 
 2.   Configure, make and install:
        # ./configure                                                        
        # make                                                               
        # make install                                                       
      You can pass options to configure. Use ./configure --help or read the
    README file, for more information.

  The binaries are installed in /usr/local/bin and /usr/local/sbin. The
configuration files are found under /usr/local/etc/raddb.

  If something went wrong, check the INSTALL and README included with the
source. The [] RADIUS FAQ also contains
valuable information.

3.2. Configuring FreeRADIUS

  FreeRADIUS has a big and mighty configuration file. It's so big, it has
been split into several smaller files that are just "included" into the main
radius.conf file.

  There is numerous ways of using and setting up FreeRADIUS to do what you
want: i.e., fetch user information from LDAP, SQL, PDC, Kerberos, etc. In
this document, user information from a plain text file, users, is used.

Tip The configuration files are thoroughly commented, and, if that is not    
    enough, the doc/ folder that comes with the source contains additional   

Configuring FreeRADIUS

 1.   The configuration files can be found under /usr/local/etc/raddb/
        # cd /usr/local/etc/raddb/                                           
 2.   Open the main configuration file radiusd.conf, and read the comments!
    Inside the encrypted PEAP tunnel, an MS-CHAPv2 authentication mechanism
    is used.
     a.   MPPE [[] RFC3078] is responsible
        for sending the PMK to the AP. Make sure the following settings are
            # under MODULES, make sure mschap is uncommented!                
            mschap {                                                         
              # authtype value, if present, will be used                     
              # to overwrite (or add) Auth-Type during                       
              # authorization. Normally, should be MS-CHAP                   
              authtype = MS-CHAP                                             
              # if use_mppe is not set to no, mschap will                    
              # add MS-CHAP-MPPE-Keys for MS-CHAPv1 and                      
              # MS-MPPE-Recv-Key/MS-MPPE-Send-Key for MS-CHAPv2              
              use_mppe = yes                                                 
              # if mppe is enabled, require_encryption makes                 
              # encryption moderate                                          
              require_encryption = yes                                       
              # require_strong always requires 128 bit key                   
              # encryption                                                   
              require_strong = yes                                           
              authtype = MS-CHAP                                             
              # The module can perform authentication itself, OR             
              # use a Windows Domain Controller. See the radius.conf file    
              # for how to do this.                                          
     b.   Also make sure the "authorize" and "authenticate" contains:
            authorize {                                                      
            authenticate {                                                   
                 #  MSCHAP authentication.                                   
                 Auth-Type MS-CHAP {                                         
                 #  Allow EAP authentication.                                
 3.   Then, change the clients.conf file to specify what network it's
       # Here, we specify which network we're serving                        
       client {                                               
            # This is the shared secret between the Authenticator (the       
            # access point) and the Authentication Server (RADIUS).          
            secret          = SharedSecret99                                 
            shortname       = testnet                                        
 4.   The eap.conf should also be pretty straightforward.
     a.   Set "default_eap_type" to "peap":
              default_eap_type = peap                                        
     b.   Since PEAP is using TLS, the TLS section must contain:
            tls {                                                            
                # The private key password                                   
                private_key_password = SecretKeyPass77                       
                # The private key                                            
                private_key_file = ${raddbdir}/certs/cert-srv.pem            
                #  Trusted Root CA list                                      
                CA_file = ${raddbdir}/certs/demoCA/cacert.pem                
                dh_file = ${raddbdir}/certs/dh                               
                random_file = /dev/urandom                                   
     c.   Find the "peap" section, and make sure it contain the following:
              peap {                                                         
                #  The tunneled EAP session needs a default                  
                #  EAP type, which is separate from the one for              
                #  the non-tunneled EAP module.  Inside of the               
                #  PEAP tunnel, we recommend using MS-CHAPv2,                
                #  as that is the default type supported by                  
                #  Windows clients.                                          
                default_eap_type = mschapv2                                  
 5.   The user information is stored in a plain text file users. A more
    sophisticated solution to store user information may be preferred (SQL,
    LDAP, PDC, etc.).
      Make sure the users file contains the following entry:
       "testuser"      User-Password == "Secret149"                          

4. Supplicant: Setting up Xsupplicant

  The Supplicant is usually a laptop or other (wireless) device that requires
authentication. Xsupplicant does the bidding of being the "Supplicant" part
of the IEEE 802.1X-2001 standard.

4.1. Installing Xsupplicant

Installing Xsupplicant

 1.   Download the latest source from from [] http://
        # cd /usr/local/src                                                               
        # wget 
        # tar zxfv xsupplicant-1.0.tar.gz                                                 
        # cd xsupplicant                                                                  
 2.   Configure, make, and install:
        # ./configure                                                        
        # make                                                               
        # make install                                                       
 3.   If the configuration file wasn't installed (copied) into the "etc"
    folder, do it manually:
        # mkdir -p /usr/local/etc/1x                                         
        # cp etc/tls-example.conf /usr/local/etc/1x                          

  If installation fails, check the README and INSTALL files included with the
source. You may also check out the official documentation.

4.2. Configuring Xsupplicant

Configuring Xsupplicant

 1.   The Supplicant must have access to the root certificate.
      If the Supplicant needs to authenticate against the Authentication
    Server (authentication both ways), the Supplicant must have certificates
    as well.
      Create a certificate folder, and move the certificates into it:
        # mkdir -p /usr/local/etc/1x/certs                                   
        # cp root.pem /usr/local/etc/1x/certs/                               
        # (copy optional client certificate(s) into the same folder)         
 2.   Open and edit the configuration file:
       # startup_command: the command to run when Xsupplicant is first started.    
       #   This command can do things such as configure the card to associate with 
       #   the network properly.                                                   
       startup_command = <BEGIN_COMMAND>/usr/local/etc/1x/<END_COMMAND>  
      The will be created shortly.
 3.   When the client is authenticated, it will transmit a DHCP request or
    manually set an IP address. Here, the Supplicant sets its IP address
    manually in
       # first_auth_command: the command to run when Xsupplicant authenticates to     
       #   a wireless network for the first time.  This will usually be used to       
       #   start a DHCP client process.                                               
       #first_auth_command = <BEGIN_COMMAND>dhclient %i<END_COMMAND>                  
       first_auth_command = <BEGIN_COMMAND>/usr/local/etc/1x/<END_COMMAND> 
 4.   Since "-i" is just for debugging purpose (and may go away according to
    the developers), "allow_interfaces" must be set:
       allow_interfaces = eth0                                               
       deny_interfaces = eth1                                                
 5.   Next, under the "NETWORK SECTION", we'll configure PEAP:
       # We'll be using PEAP                                                    
       allow_types = eap_peap                                                   
       # Don't want any eavesdropper to learn the username during the           
       # first phase (which is unencrypted), so 'identity hiding' is            
       # used (using a bogus username).                                         
       identity = <BEGIN_ID>anonymous<END_ID>                                   
       eap-peap {                                                               
          # As in tls, define either a root certificate or a directory          
          # containing root certificates.                                       
          root_cert = /usr/local/etc/1x/certs/root.pem                          
          #root_dir = /path/to/root/certificate/dir                             
          #crl_dir = /path/to/dir/with/crl                                      
          chunk_size = 1398                                                     
          random_file = /dev/urandom                                            
          #cncheck =   # Verify that the server certificate 
                                           # has this value in its CN field.    
          #cnexact = yes                   # Should it be an exact match?       
          session_resume = yes                                                  
          # Currently 'all' is just mschapv2.                                   
          # If no allow_types is defined, all is assumed.                       
          #allow_types = all # where all = MSCHAPv2, MD5, OTP, GTC, SIM         
          allow_types = eap_mschapv2                                            
          # Right now, you can do any of these methods in PEAP:                 
          eap-mschapv2 {                                                        
            username = <BEGIN_UNAME>testuser<END_UNAME>                         
            password = <BEGIN_PASS>Secret149<END_PASS>                          
 6.   The Supplicant must first associate with the access point. The script does that job. It is also the first command Xsupplicant
    Note Notice the bogus key we give to iwconfig (enc 000000000)! This key  
         is used to tell the driver to run in encrypted mode. The key gets   
         replaced after successful authentication. This can be set to enc off
         only if encryption is disabled in the AP (for testing purposes).    
      Both and must be saved under /usr/local/etc/1x/.
       echo "Starting"                                             
       # Take down interface (if it's up)                                     
       /sbin/ifconfig eth0 down                                               
       # To make sure the routes are flushed                                  
       sleep 1                                                                
       # Configuring the interface with a bogus key                           
       /sbin/iwconfig eth0 mode managed essid testnet enc 000000000           
       # Bring the interface up and make sure it listens to multicast packets 
       /sbin/ifconfig eth0 allmulti up                                        
       echo "Finished"                                             
 7.   This next file is used to set the IP address statically. This can be
    omitted if a DHCP server is present (as it typically is, in many access
       echo "Starting"                                           
       # Assigning an IP address                                             
       /sbin/ifconfig eth0 netmask                 
       echo "Finished"                                           

5. Authenticator: Setting up the Authenticator (Access Point)

  During the authentication process, the Authenticator just relays all
messages between the Supplicant and the Authentication Server (RADIUS). EAPOL
is used between the Supplicant and the Authenticator; and, between the
Authenticator and the Authentication Server, UDP is used.

5.1. Access Point

  Many access point have support for 802.1X (and RADIUS) authentication. It
must first be configured to use 802.1X authentication.

Note Configuring and setting up 802.1X on the AP may differ between vendors. 
     Listed below are the required settings to make a Cisco AP350 work. Other
     settings to TIKP, CCMP etc. may also be configured.                     

  The AP must set the ESSID to "testnet" and must activate:


Figure AP350: The RADIUS configuration screen for a Cisco AP-350

��*�  802.1X-2001: Make sure the 802.1X Protocol version is set to 
    "802.1X-2001". Some older Access Points support only the draft version of
    the 802.1X standard (and may therefore not work).
��*�  RADIUS Server: the name/IP address of the RADIUS server and the shared
    secret between the RADIUS server and the Access Point (which in this
    document is "SharedSecret99"). See figure AP350.
��*�  EAP Authentication: The RADIUS server should be used for EAP


Figure AP350-2: The Encryption configuration screen for a Cisco AP-350

��*�  Full Encryption to allow only encrypted traffic. Note that 802.1X may
    be used without using encryption, which is nice for test purposes.
��*�  Open Authentication to make the Supplicant associate with the Access
    Point before encryption keys are available. Once the association is done,
    the Supplicant may start EAP authentication.
��*�  Require EAP for the "Open Authentication". That will ensure that only
    authenticated users are allowed into the network.

5.2. Linux Authenticator

  An ordinary Linux node can be set up to function as a wireless Access Point
and Authenticator. How to set up and use Linux as an AP is beyond the scope
of this document. Simon Anderson's Linux Wireless Access Point HOWTO may be
of guidance.

6. Testbed

6.1. Testcase


figure testbed: A wireless node request authentication.

  Our testbed consists of two nodes and one Access Point (AP). One node
functions as the Supplicant (WN), the other as the back-end Authentication
Server running RADIUS (AS). The Access Point is the Authenticator. See figure
testbed for explanation.

Important It is crucial that the Access Point be able to reach (ping) the    
          Authentication Server, and vice versa!                             

6.2. Running some tests

Running some tests

 1.   The RADIUS server is started in debug mode. This produces a lot of
    debug information. The important snippets are below:
      # radiusd -X                                                           
      Starting - reading configuration files ...                             
      reread_config:  reading radiusd.conf                                   
      Config:   including file: /usr/local/etc/raddb/proxy.conf              
      Config:   including file: /usr/local/etc/raddb/clients.conf            
      Config:   including file: /usr/local/etc/raddb/snmp.conf               
      Config:   including file: /usr/local/etc/raddb/eap.conf                
      Config:   including file: /usr/local/etc/raddb/sql.conf                
      Module: Loaded MS-CHAP                                                 
       mschap: use_mppe = yes                                                
       mschap: require_encryption = no                                       
       mschap: require_strong = no                                           
       mschap: with_ntdomain_hack = no                                       
       mschap: passwd = "(null)"                                             
       mschap: authtype = "MS-CHAP"                                          
       mschap: ntlm_auth = "(null)"                                          
      Module: Instantiated mschap (mschap)                                   
      Module: Loaded eap                                                     
       eap: default_eap_type = "peap" (1)                                    
       eap: timer_expire = 60                                                
       eap: ignore_unknown_eap_types = no                                    
       eap: cisco_accounting_username_bug = no                               
      rlm_eap: Loaded and initialized type md5                               
       tls: rsa_key_exchange = no (2)                                        
       tls: dh_key_exchange = yes                                            
       tls: rsa_key_length = 512                                             
       tls: dh_key_length = 512                                              
       tls: verify_depth = 0                                                 
       tls: CA_path = "(null)"                                               
       tls: pem_file_type = yes                                              
       tls: private_key_file = "/usr/local/etc/raddb/certs/cert-srv.pem"     
       tls: certificate_file = "/usr/local/etc/raddb/certs/cert-srv.pem"     
       tls: CA_file = "/usr/local/etc/raddb/certs/demoCA/cacert.pem"         
       tls: private_key_password = "SecretKeyPass77"                         
       tls: dh_file = "/usr/local/etc/raddb/certs/dh"                        
       tls: random_file = "/usr/local/etc/raddb/certs/random"                
       tls: fragment_size = 1024                                             
       tls: include_length = yes                                             
       tls: check_crl = no                                                   
       tls: check_cert_cn = "(null)"                                         
      rlm_eap: Loaded and initialized type tls                               
       peap: default_eap_type = "mschapv2" (3)                               
       peap: copy_request_to_tunnel = no                                     
       peap: use_tunneled_reply = no                                         
       peap: proxy_tunneled_request_as_eap = yes                             
      rlm_eap: Loaded and initialized type peap                              
       mschapv2: with_ntdomain_hack = no                                     
      rlm_eap: Loaded and initialized type mschapv2                          
      Module: Instantiated eap (eap)                                         
      Module: Loaded files                                                   
       files: usersfile = "/usr/local/etc/raddb/users" (4)                   
      Module: Instantiated radutmp (radutmp)                                 
      Listening on authentication *:1812                                     
      Listening on accounting *:1813                                         
      Ready to process requests. (5)                                         
    (1)   Default EAP type is set to PEAP.
    (2)   RADIUS's TLS settings are initiated here. The certificate type,
        location, and password are listet here.
    (3)   Inside the PEAP tunnel, MS-CHAPv2 is used.
    (4)   The username/password information is found in the users file.
    (5)   RADIUS server started successfully. Waiting for incoming requests.
    The radius server is now ready to process requests!
      The most interesting output is included above. If you get any error
    message instead of the last line, go over the configuration (above)
 2.   Now the Supplicant is ready to get authenticated. Start Xsupplicant in
    debug mode. Note that we'll see output produced by the two startup
    scripts: and
      # xsupplicant -c /usr/local/etc/1x/1x.conf -i eth0 -d 6                
      Starting /etc/1x/                                            
      Finished /etc/1x/                                            
      Starting /etc/1x/                                           
      Finished /etc/1x/                                           
 3.   At the same time, the RADIUS server is producing a lot of output. Key
    snippets are shown below:
      rlm_eap: Request found, released from the list                                                   
      rlm_eap: EAP/peap                                                                                
      rlm_eap: processing type peap                                                                    
      rlm_eap_peap: Authenticate                                                                       
      rlm_eap_tls: processing TLS (1)                                                                  
      eaptls_verify returned 7                                                                         
      rlm_eap_tls: Done initial handshake                                                              
      eaptls_process returned 7                                                                        
      rlm_eap_peap: EAPTLS_OK (2)                                                                      
      rlm_eap_peap: Session established.  Decoding tunneled attributes.                                
      rlm_eap_peap: Received EAP-TLV response.                                                         
      rlm_eap_peap: Tunneled data is valid.                                                            
      rlm_eap_peap: Success                                                                            
      rlm_eap: Freeing handler                                                                         
      modcall[authenticate]: module "eap" returns ok for request 8                                     
    modcall: group authenticate returns ok for request 8                                               
    Login OK: [testuser/<no User-Password attribute>] (from client testnet port 37 cli 0002a56fa08a)   
    Sending Access-Accept of id 8 to (3)                                              
            MS-MPPE-Recv-Key = 0xf21757b96f52ddaefe084c343778d0082c2c8e12ce18ae10a79c550ae61a5206 (4)  
            MS-MPPE-Send-Key = 0x5e1321e06a45f7ac9f78fb9d398cab5556bff6c9d003cdf8161683bfb7e7af18      
            EAP-Message = 0x030a0004                                                                   
            Message-Authenticator = 0x00000000000000000000000000000000                                 
            User-Name = "testuser"                                                                     
    (1)   TLS session startup. Doing TLS-handshake.
    (2)   The TLS session (PEAP-encrypted tunnel) is up.
    (3)   The Supplicant has been authenticated successfully by the RADIUS
        server. An "Access-Accept" message is sent.
    (4)   The MS-MPPE-Recv-Key [[] RFC2548
        section 2.4.3] contains the Pairwise Master Key (PMK) destined to the
        Authenticator (access point), encrypted with the MPPE Protocol
        [[] RFC3078], using the shared
        secret between the Authenticator and Authentication Server as key.
        The Supplicant derives the same PMK from MK, as described in Key
 4.   The Authenticator (access point) may also show something like this in
    its log:
      00:02:16 (Info): Station 0002a56fa08a Associated                         
      00:02:17 (Info): Station=0002a56fa08a User="testuser" EAP-Authenticated  

  That's it! The Supplicant is now authenticated to use the Access Point!

7. Note about driver support and Xsupplicant

  As described in Key Management, one of the big advantages of using Dynamic
WEP/802.11i with 802.1X is the support for session keys. A new encryption key
is generated for each session.

  Xsupplicant only supports "Dynamic WEP" as of this writing. Support for WPA
and RSN/WPA2 (802.11i) is being worked on, and is estimated to be supported
at the end of the year/early next year (2004/2005), according to Chris
Hessing (one of the Xsupplicants developers).

  Not all wireless drives support dynamic WEP, nor WPA. To use RSN (WPA2),
new support in hardware may even be required. Many older drivers assume only
one WEP key will be used on the network at any time. The card is reset
whenever the key is changed to let the new key take effect. This triggers a
new authentication, and there is a never-ending loop.

  At the time of writing, most of the wireless drivers in the base Linux
kernel require patching to make dynamic WEP/WPA work. They will, in time, be
upgraded to support these new features. Many drivers developed outside the
kernel, however, support for dynamic WEP; HostAP, madwifi, Orinoco, and atmel
should work without problems.

  Instead of using Xsupplicant, []
wpa_supplicant may be used. It has support for both WPA and RSN (WPA2), and a
wide range of EAP authentication methods.

8. FAQ

  Do not forget to check out the FAQ section of both the [http://] FreeRADIUS (highly recommended!) and [http://]  
Xsupplicant Web sites!

8.1.   Is it possible to allow user-specific Xsupplicant configuration, to
    avoid having a global configuration file?
8.2. I don't want to use PEAP; can I use EAP-TTLS or EAP-TLS instead?
8.3.   Can I use a Windows Supplicant (client) instead of GNU/Linux?
8.4.   Can I use a Active Directory to authenticate users?
8.5.   Is there any Windows Supplicant clients available?

8.1. Is it possible to allow user-specific Xsupplicant configuration, to
avoid having a global configuration file?

No, not at the moment.

8.2. I don't want to use PEAP; can I use EAP-TTLS or EAP-TLS instead?

Yes. To use EAP-TTLS, only small changes to the configuration used in this
document are required. To use EAP-TLS, client certificates must be used as

8.3. Can I use a Windows Supplicant (client) instead of GNU/Linux?

Yes. Windows XP SP1/Windows 2000 SP3 has support for PEAP MSCHAPv2 (used in
this document). A Windows HOWTO can be found here: FreeRADIUS/WinXP
Authentication Setup

8.4. Can I use a Active Directory to authenticate users?

Yes. FreeRADIUS can authenticate users from AD by using "ntlm_auth".

8.5. Is there any Windows Supplicant clients available?

Yes. As of Windows XP SP1 or Windows 2000 SP3, support for WPA (PEAP/
MS-CHAPv2) is supported. Other clients include (not tested) [http://] Secure W2 (free for non-commercial) and [http://] WIRE1X. [] Funk Software also
has a commercial client available.

9. Useful Resources

  Only IEEE standards older than 12 months are available to the public in
general (through the "Get IEEE 802 Program"). So the new 802.11i and 
802.1X-2004 standards documents are not available. You must be a IEEE
participant to get hold of any drafts/work in progress papers (which actually
isn't that hard - just join a mailing list and say you are interested).


 1. FreeRADIUS Server Project[]   http://
 2. Open1x: Open Source implementation of IEEE 802.1X (Xsupplicant)[http://]
 3. The Open1x User's Guide
 4. Port-Based Network Access Control (802.1X-2001)[
 5. RFC2246: The TLS Protocol Version 1.0
 6. RFC2459: Internet X.509 Public Key Infrastructure - Certificate and CRL
 7. RFC2548: Microsoft Vendor-specific RADIUS Attributes
 8. RFC2716: PPP EAP TLS Authentication Protocol
 9. RFC2865: Remote Authentication Dial-In User Service (RADIUS)[http://]
10. RFC3079: Deriving Keys for use with Microsoft Point-to-Point Encryption
11. RFC3579: RADIUS Support For EAP[]
12. RFC3580: IEEE 802.1X RADIUS Usage Guidelines[
13. RFC3588: Diameter Base Protocol[]
14. RFC3610: Counter with CBC-MAC (CCM)[]
15. RFC3748: Extensible Authentication Protocol (EAP)[
16. Linux Wireless Access Point HOWTO [
17. SSL Certificates HOWTO
18. OpenSSL: x509(1)

10. Copyright, acknowledgments and miscellaneous

10.1. Copyright and License

Copyright (c) 2004 Lars Strand.

  Permission is granted to copy, distribute and/or modify this document under
the terms of the GNU Free Documentation License, Version 1.2 or any later
version published by the Free Software Foundation; with no Invariant
Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the
license is included in the section entitled "GNU Free Documentation License".

10.2. How this document was produced

This document was written in DocBook XML using Emacs.

10.3. Feedback

  Suggestions, corrections, additions wanted. Contributors wanted and
acknowledged. Flames not wanted.

  I can always be reached at <lars strand at gnist org>

  Homepage: []

10.4. Acknowledgments

  Thanks to Andreas Hafslund <andreha at unik no> and Thales Communication
for initial support.

  Also thanks to Artur Hecker <hecker at enst fr>, Chris Hessing <chris
hessing at utah edu>, Jouni Malinen <jkmaline at cc hut fi> and Terry Simons
<galimore at mac com> for valuable feedback!

  Thanks to Rick Moen <rick at linuxmafia com> for doing a language review!

A. GNU Free Documentation License

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    Back-Cover Texts. A copy of the license is included in the section
    entitled "GNU Free Documentation License".
If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts,
replace the "with...Texts." line with this:

      with the Invariant Sections being LIST THEIR TITLES, with the
    Front-Cover Texts being LIST, and with the Back-Cover Texts being LIST.
If you have Invariant Sections without Cover Texts, or some other combination
of the three, merge those two alternatives to suit the situation.

If your document contains nontrivial examples of program code, we recommend
releasing these examples in parallel under your choice of free software
license, such as the GNU General Public License, to permit their use in free

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