What are the causes of the L2TP dialup failure

The causes of the L2TP dialup failure are as follows:

-The firewall deployed on the public network or the built-in firewall on the PC discards L2TP packets.
-The corresponding L2TP port, usually UDP port 1701, is disabled or occupied. For example: ACL or NAT is configured on the port.
-The user name and password configured on the LAC are incorrect, or no related user is configured on the LNS.
-The configuration address, such as the static address of the VT interface, is incorrect.
-The tunnel authentication modes are different.
-LCP renegotiation is not configured.
-The address pool cannot meet user requirement or no address pool is configured.
-No gateway address is reserved in the IP address pool, so that the gateway address is allocated to users.
-The LAC and LNS have no reachable routes to each other.
-An incorrect remote tunnel name is specified in the L2TP group view.
-The authentication domain is incorrectly configured.
-The control packets sent by the PC client do not carry the SQ number, so that the L2TP negotiation fails.
-When IPSec encryption is used, the IPSec parameters on both ends are different.

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