Value,Description,Reference
0,Reserved,[RFC2661]
1,Textual username/password exchange,[RFC2661]
2,PPP CHAP,[RFC2661]
3,PPP PAP,[RFC2661]
4,No Authentication,[RFC2661]
5,Microsoft CHAP Version 1 (MSCHAPv1),[RFC2661]
6,Reserved,
7,EAP,[draft-ietf-l2tpext-proxy-authen-ext-eap-00]