Private RADIUS attribute defined by Microsoft. The attribute number is 26, vendor ID is 311, and sub-attribute ranges from 1 to 255. For details, see the following:
MS-CHAP-Response (1)
MS-CHAP-Error (2)
MS-CHAP-CPW-2 (4)
MS-CHAP-NT-Enc-PW (6)
MS-CHAP-Challenge (11)
MS-MPPE-Send-Key (16)
MS-MPPE-Recv-Key (17)
MS-CHAP2-Response (25)
MS-CHAP2-Success (26)
MS-CHAP2-CPW (27)
MS-Primary-DNS-Server (28)
MS-Secondary-DNS-Server (29)