「xl2tpd」- l2tp-secrets

	l2tp-secrets - L2TPD secrets file
	The l2tp-secrets file contains challenge-response authentication information for xl2tpd, the implementation of l2tp protocol.
	The format of the file is derived from the **pap** and **chap** secrets file format used in **pppd**.
	The secrets file is composed of zero or more lines with **3 fields each**.
	Each line represents an authentication secret.
	The 3 fields represent **our hostname**, the **remote hostname** and **the secret** used in the authentication process.
		* The **first** field is for our hostname, a "*" may be used as a wildcard.
		* The **second** field is for the remote system's hostname.  Again, a "*" may be used as a wildcard.
		* The **third** field is the secret used if the previous two fields match the hostnames of the systems involved.  The secret should, ideally, be at 16 characters long (the length of an MD5 digest output), and should probably be longer to ensure sufficient security.  There is no minimum length requirement, however.


man 5 l2tp-secrets