Because MAB uses the MAC address as a username and password, make sure that the RADIUS server can differentiate MAB requests from other types of requests for network access. This precaution prevents other clients from attempting to use a MAC address as a valid credential. Cisco switches uniquely identify MAB requests by setting Attribute 6 (Service-Type) to 10 (Call-Check) in a MAB Access-Request message. Therefore, you can use Attribute 6 to filter MAB requests at the RADIUS server.
Optionally, Cisco switches can be configured to perform MAB as EAP-MD5 authentication, in which case the Service-Type attribute is set to 1 (Framed). However, because the MAC address is sent in the clear in Attribute 31 (Calling-Station-Id), MAB EAP does not offer any additional security by encrypting the MAC address in the password. In addition, because the service type for MAB EAP is the same as an IEEE 802.1X request, the RADIUS server is not able to easily differentiate MAB EAP requests from IEEE 802.1X requests.
https://www.cisco.com/c/en/us/td/docs/solutions/Enterprise/Security/TrustSec_1-99/MAB/MAB_Dep_Guide.html
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