+.B require-mppe
+Require the use of MPPE (Microsoft Point to Point Encryption). This
+option disables all other compression types. This option enables
+both 40\-bit and 128\-bit encryption. In order for MPPE to successfully
+come up, you must have authenticated with either MS-CHAP or MS-CHAPv2.
+This option is presently only supported under Linux, and only if your
+kernel has been configured to include MPPE support.
+.TP
+.B require-mppe-40
+Require the use of MPPE, with 40\-bit encryption.
+.TP
+.B require-mppe-128
+Require the use of MPPE, with 128\-bit encryption.
+.TP
+.B require-mschap
+Require the peer to authenticate itself using MS-CHAP [Microsft Challenge
+Handshake Authentication Protocol] authentication.
+.TP
+.B require-mschap-v2
+Require the peer to authenticate itself using MS-CHAPv2 [Microsft Challenge
+Handshake Authentication Protocol, Version 2] authentication.
+.TP