+* NF_LINK_DOWN. This is called when the link goes down.
+
+* NF_FORK. Called for each time pppd exists as a new process (child).
+
+
+Regarding MPPE keys and key-material for 2.5.0 release
+
+Sometimes it is necessary for a plugin to access details related to
+the authentication process. The NF_AUTH_UP callback notifier (client only)
+allows a plugin to inspect e.g. key details after authentication has been
+completed, but before the key material is cleared from memory for security
+reasons.
+
+There are in particularly 3 functions that allow one to inspect these
+keys:
+
+* bool mppe_keys_isset()
+* int mppe_get_recv_key(unsigned char *key, int length)
+* int mppe_get_send_key(unsigned char *key, int length)
+
+The first function indicates whether or not the key material is set and
+is valid. The two latter functions will allow one to obtain a copy
+of the respective receive and send keys. The return value of these
+functions is the length of the valid key material. For security reasons,
+one should take care to clear these copies when work is complete. The
+max length of MPPE receive ands send keys are up to 32 bytes long, or
+of MPPE_MAX_KEY_SIZE length.
+
+The previous definitions of MPPE_MAX_KEY_LEN is the maximum length in
+which the Linux kernel will accept for MPPE key lengths. Plugins would
+access the MPPE keys directly via the: