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802.1X is a standard that is part of 802.1, it consists in access control to a network by allowing/blocking all packets at the clienta given device's point of access into the network, including all broadcast packets, etc. It is possible on Wi-Fi, ethernet and possibly other mediums.
Upon connecting a device to an ethernet port on a switch or associating to a wireless SSID, the network switch or wifi access point (sometimes not necessarily very correctly referred to as wifi router) concerned will initially not allow any data to be transmitted/received by the device. It will request the connected device to identify itself and, upon approval of the supplied credentials by an authentication server, start accepting packets from/to between the newly connected device and the rest of the network it serves, or continue dis-allowing, in the case the authentication server did not approve the credentials.
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EAP itself is an encapsulation protocol, inside it a variety of different protocols can be run to perform authentication. An authentication protocol can be encapsulated directly inside the EAP tunnel or an encryption protocol can be, inside which then, (at least in the cases of EAP-PEAP and EAP-TTLS) eventually another instance of the EAP protocol is encapsulated, inside which, finally, the actually actual authentication protocol is encapsulated. According to the comment in the mods-available/eap config file at the beginning of the 'ttls' section, the hierarchy with EAP-TTLS is RADIUS → EAP → TLS → Diameter (protocol comparable in scope to RADIUS) → again EAP → the actual protocol used for authentication). EAP-PEAP is '@@@'x2 similar in functionality. An example of an authentication protocol that can be used for the actual authentication is MSCHAPv2.
In the case an encrypted tunnel is used, the data/attributes contained directly in the RADIUS conversation are unencrypted. The RADIUS conversation part is called the "Outer Tunnel", whereas the (Diameter?) '@@@' conversation within the TLS encryption encrypted tunnel is called the "Inner Tunnel", data/attributes sent in this conversation are encrypted. At the time of setting up the encrypted tunnel, the authentication server presents a certificate identifying itself which the supplicant may (and should) choose to verify before sending its login credentials to the server.
In the case of an Access-Accept, the wifi router NAS now allows the supplicant to join the network, or, in the case of Access-Reject, will not. Once the NAS has granted access, for 802.1X/RADIUS/authentication server, the job is done, and the supplicant becomes part of the 192.168.254.0/24 network's broadcast domain. The authentication server , can specify attributes in the replying packet to give the NAS additional instructions, for example, it might request the NAS to place the newly connected supplicant in a specific VLAN, or it might specify for how long the supplicant is allowed to remain connected, or It can now initiate a DHCP request for an IP address or any other action as may be appropriate. The authentication server is able to log that the user connected along with information from attributes the NAS might have sent, generally this includes the MAC address of the supplicant, MAC address of the NAS, username (if authentication was done by username/password) and more depending on the NAS model. The supplicant can now initiate a DHCP request for an IP address or any other action as may be appropriate.
EAP and RADIUS have support for a great variety of features or different methods that can be encapsulated there-in 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). EAP, being a tunneling protocol inside which a suitable protocol for performing authentication needs to be used, gives flexibility in usable authentication protocols without requiring specific support for that protocol by the NAS, as long as it 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.
- Please see the "Supplicant configuration" section 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.
- EAP-TLS is an authentication method that can be used to authenticate supplicants based on client certificates.
Things to mention:
Re-auth undesired behavior
Protocols used: EAP, MSCHAP, PEAP, TTLS, TLS Difference between auth systems: PEAP, TTLS, TLS
Re-auth undesired behavior
- Done
features supported by TP-Link NASes - Done
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