What are possible causes for L2TP dial-up failures of the AR router

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Possible causes for L2TP dialup failures are as follows:
- The firewall is configured on the public network or the local PC has the firewall, so L2TP packets are discarded.
- When corresponding L2TP port is disabled or occupied, UDP port 1701 is often used. For example, ACL and NAT are configured. - The user name and password of the LAC are incorrect, or no users are specified for the LNS.
- The configured address is incorrect. For example, the statically configured address of the VT interface is incorrect.
- Tunnel authentication modes are different.
- LCP renegotiation is not configured.
- The IP address allocation is improper. The IP address pool has a small address range or not configured.
- Gateway addresses are not configured in the IP address pool, so gateway addresses are allocated to clients.
- There are unreachable routes.
- In the L2TP group view, the specified tunnel name at the remote end is incorrect.
- The configured authentication domain is incorrect.
- L2TP negotiation fails because control packets sent by clients of the local PC do not carry the SQ.
- When IPSec encryption is used, the IPSec parameters on the two ends of the tunnel are inconsistent.

Other related questions:
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.

Possible causes of a failure of an interconnection between WDM equipment and a router
The possible causes are as follows: Possible cause 1: The line between the WDM equipment and the data equipment is faulty. Possible cause 2: The client-side parameters of the interconnected boards on WDM products are incorrectly configured. Possible cause 3: An interconnected board is faulty.

Causes for the L2TP dialup failure
The possible causes are as follows: - L2TP packets are discarded because the firewall or the PC with built-in firewall on the public network discards L2TP packets. - The corresponding ports of L2TP are disabled or occupied. Generally, UDP port 1701 is used. For example, ACL and NAT use this port. - The user name and password are incorrectly configured on the LAC, or no user is configured on the LNS. - The address is incorrectly configured. For example, the static address of the VT interface is incorrect. - Tunnel authentication modes are different. - LCP renegotiation is not configured. - The addresses are improperly allocated. The address pool is small or is not set. - The IP address pool is not configured with the gateway address, so that the gateway address is also allocated to the clients. - Unreachable routes exist at both ends. - In the L2TP group view, the specified remote tunnel name is incorrect. - The authentication domain is configured incorrectly. - Control packets sent by the built-in client of the PC do not carry the SQ serial number. As a result, L2TP negotiation fails. - IPSec parameters configured at both ends are inconsistent.

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