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  1. The RADIUS protocol also includes the possibility for the NAS to send accounting information to the authentication server for the purpose of logging user activity, this is on a separate port, UDP 1813, this has not been investigated as it seems to be not supported by the NASes we have, and presumably is not on any NAS in the price range.
  2. The RADIUS protocol also includes the possibility for the authentication server to initiate a connection to the NAS and inform it to disconnect a currently logged in user, but again, this has not been investigated much as it seems to be not supported by the NASes we have, and presumably is not on any NAS in the price range.

  3. In absence of the above mentioned feature, once a user has connected, there is no way to disconnect them other than rebooting the NAS. If the system administrator chooses to disable a user account on the authentication server, the user will be denied access only from the next time they try to connect, if they are already connected at the time of disabling the account, they will remain connected for the moment. It is possible for the authentication server to specify with the "Session-Timeout" and "Termination-Action" attributes of the Access-Accept packet for how long a user is allowed to remain connected without repeating authentication (again subject to NAS supporting). Depending on the NAS and supplicant models it has been observed that there can be a new authentication request, in the case of wifi, when the supplicant moves out of range of the wifi and then comes back, or when the user switches wifi off and on again on the supplicant, but might also not be the case.
  4. A "User-Name" attribute is usually provided in both the outer and inner tunnels, often referred to as outer identity and inner identity, respectively. It is often suggested to send the real username only in the inner tunnel for privacy reasons as it is encrypted, and send the string 'anonymous' as User-Name in the outer tunnel. It was found, however, to be unreasonably difficult, if at all possible, to configure Mac OS, Windows and iPhone clients to do so. The 'User-Name' attribute in the outer tunnel is still useful as a realm for the user may be specified and a RADIUS server might need to forward the request to another RADIUS server, based on the specified realm and might be unable to read the encrypted inner-tunnel. If the outer user name is anonymized and a realm needs to be specified, the attribute would read 'anonymous@realm'.
  5. It is possible for a FreeRADIUS server to forward a request to an upstream RADIUS server to handle. The answer then gets sent back and the local FreeRADIUS server forwards it to the client. It is possible (or maybe most of the time/always the case?) that intermediary RADIUS servers are not able to decrypt the data within the encrypted inner-tunnel, and do not have access to it. One way for a RADIUS server to determine whether it should answer a given query itself or forward it upstream is to look at the realm part of the outer identity provided in the outer tunnel.
  6. According to Wikipedia, there is a similar protocol evolved from RADIUS, called Diameter:
  7. In Debian, the FreeRADIUS daemon is called freeradius. Apparently, in many other environments it is called radiusd.
  8. When debugging, it is recommended to stop the FreeRADIUS daemon and run freeradius -X in a terminal. A lot of debug information is then printed on the screen, which can be used to see what's happening. This is stressed a lot on the FreeRADIUS wiki and users' mailing list.
  9. A system called RSN pre-authentication (sometimes called WPA2 pre-authentication) can be used, when multiple NASes are installed in a network, which allows the NASes to talk amongst themselves and inform other NASes about supplicants that have authenticated through them. This allows a wireless supplicant that moves within the building to connect to a different NAS without having to repeat RADIUS authentication. This feature has not been investigated much. It might be that it is only available on wireless LAN NASes. It is suspected that this feature is the cause of the Session-Timeout / Termination-Action attributes not working in some corner cases (observed sometimes when the supplicant roamed between different NASes in a particular order), resulting in the supplicant remaining connected to the network longer than the specified limit, without repeating authentication to the RADIUS server.
  10. Through a rather limited amount of research in this regards, it is my understanding that for each supplicant a different key is generated and used to encrypt wireless communication between it and the NAS once authenticated, and is generated in part using also a key provided by the RADIUS server, and supplicant and NAS MAC addresses. A supplicant, during authentication specifies its MAC address as well as login credentials, which is logged in the RADIUS server along with user details. As per tests, it is inferred that, after a supplicant connects to the wifi network, the NAS does not allow the supplicant to send packets with a source MAC address other than the one specified during authentication. This when connecting. This was tested on a TP-Link TL WR740N, with 802.1X wireless security as well as with wireless security disabled, and on a TP-Link Archer C20 with wireless security disabled using 'ostinato' (package available in Debian repositories) to transmit test packets. This protects against MAC spoofing once a user is logged into the network. 
  11. There are two different WPA standards, WPA and WPA2. The latter is the proper one, and the former was released as an interim solution to be applied on existing devices with inadequate hardware for running WPA2 due to the urgency of upgrading from WEP which was at the time discovered to be significantly insecure. Similarly there is an "encryption" setting in most NASes with two possible settings, TKIP and AES, where AES is the proper solution, and TKIP the interim one.
  12. Please see the "Supplicant configuration" and "WiFi access point (NAS) configuration" sections of the "802.1X secured wifi installation" page's "Installation" child page for more information about features supported by and behavior specific to some NAS models and supplicants.
  13. EAP-TLS is an authentication protocol that can be used to authenticate supplicants based on client certificates.
  14. Depending on the chosen authentication method, different encryption algorithms may or may not be supported for storage of the passwords in the user database. A table showing some of the authentication methods with the supported algorithms is here: