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EAP and RADIUS are both general purpose protocols that take care of communication. They have support for a great variety of features or different methods to perform authentication (e.g. it is possible to use different protocols that authenticate the user using a username and password, or using client certificates, or even SIM cards), but it is still up to the supplicant, NAS and authentication server implementations to choose which ones they support or not (even different NASes have been seen to send MAC addresses in different format, e.g. TP-Link Archer C20 sends 01-23-45-67-89-AB, while TP-Link TD-W8968 sends 0123456789ab. TP-Link TL-WR740N, in the case of the NAS MAC address, sends 01-23-45-67-89-AB:SSID, where SSID is the configured wireless SSID). In fact, EAP is only a tunneling protocol inside which a suitable protocol for performing authentication needs to be used. This makes it possible to have flexibility in usable authentication protocols whilst maintaining compatibility with any NAS, as long as the authentication protocol is supported by both the supplicant and authentication server.

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• 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.

• 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.

• 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.
• 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 necessary as a realm for the user may be specified which might need to be accessed by a RADIUS server which might forward the request and be unable to read the encrypted part. If the user name is anonymized and a realm needs to be specified, the attribute would read 'anonymous@realm'.
• 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. Usually intermediary RADIUS servers are not able to decrypt the data within the SSL 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 domain part of the outer identity provided in the outer tunnel.
• According to Wikipedia, there is a similar protocol evolved from RADIUS, called Diameter: https://en.wikipedia.org/wiki/Diameter_(protocol)
• In Debian, the FreeRADIUS daemon is called freeradius. Apparently, in many other environments it is called radiusd.
• 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.
• 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. I have not explored this feature much. It might be that it is only available on wireless LAN NASes.
• Through a rather limited amount of research in this regards, it is my understanding that for each supplicant a different key is used to encrypt traffic between it and the NAS, and is generated partly using information provided by the RADIUS, partly using the supplicant's and NAS MAC addresses, and presumably more information. A supplicant, during authentication specifies its MAC address as well as login credentials, which is logged in the RADIUS server along with user details. After authentication, the NAS does not allow the supplicant to send packets with a source MAC address other than the one specified during authentication. '@@@' (to be verified) This protects against MAC spoofing once a user is logged into the network.
• 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 are two encryption algorithms '@@@', TKIP and AES, where AES is the proper one, and TKIP the interim one.

Things to mention:

Proxying

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Difference between auth systems: PEAP, TTLS, TLS

CertificatesWifi keying, session timeout, etc. protections against MAC-spoofing, etc.

SSL tunnel

Terminology: AP, wifi routerWPA2 preauthentication (RSN)

Re-auth undesired behavior

WPA/WPA2

TKIP/AES

Terminology: NAS, RADIUS, FreeRADIUS, Authenticator, Supplicant, Authentication server - Done

Diameter - Done

Wifi keying, session timeout, etc. protections against MAC-spoofing, etc. - Done

Outer and inner identity and MAC/Windows support - Done

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freeradius -X. radiusd vs freeradius - Done

WPA/WPA2 - Done

TKIP/AES - Done

FreeRADIUS configuration files

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