As per RFC 3748
All EAP implementations MUST support Types 1-4, which are defined in this document, and SHOULD support Type 254. Implementations MAY support other Types defined here or in future RFCs.
1 Identity
2 Notification
3 Nak (Response only)
4 MD5-Challenge
5 One Time Password (OTP)
6 Generic Token Card (GTC)
254 Expanded Types
255 Experimental use