Why is there a delay in accessing the private network after successful L2TP dialup

The possible causes are as follows:
-L2TP encapsulates IP packets. As a result, the IP packet length becomes longer. If the IP packet length exceeds the MTU during transmission, the IP packets are fragmented and sent. The receiver needs to reassemble and parse the fragments. Fragmentation and reassembly consume CPU resources. When there are many fragments, CPU resources may be insufficient. In this case, the access is slow and packets are discarded.
The MTU of the virtual template interface must be smaller than or equal to the L2TP packet header length (42 bytes with the sequence number or 38 bytes without the sequence number) subtracted from the MTU value on the physical outbound interface (1500 bytes by default). For example, when the default MTU on the physical outbound interface is 1500 bytes and the L2TP packet header length is 42 bytes, the MSS must be smaller than or equal to 1458.
-For TCP packets, when the length of TCP packets encapsulated with the L2TP header is larger than the MTU, there is a delay in performing the ping operation for the private network. As a result, an exception occurs in web page opening and remote login fails. You are advised to adjust the MSS of the virtual template interface so that the length of TCP packets encapsulated with the L2TP header is not larger than the MTU.

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