Internet access is slow after a PPPoE dialup link on an AR router is switched over

Modify the TCP MSS value of the device, and set the state of the Dialer interface protocol after PPPoE dialup fails to Down for link switchover.
Example: Modify the TCP MSS value.
[Huawei]interface Dialer 1
[Huawei-Dialer1]tcp adjust-mss 1200
Example: Set the state of the Dialer interface protocol after PPPoE dialup fails to Down.
[Huawei]interface Dialer 1
[Huawei-Dialer1]dialer number 1 autodial
The causes are as follows:
The TCP MSS value is used to control the maximum transmission load of TCP packets, and it is determined according to the negotiation between the client and server. Generally, it is set to 1460. Plus 20-byte IP header, 20-byte TCP header, and 8-byte PPPoE header, the MTU of TCP packets is 1508 bytes. However, the MTU of network device interfaces is 1500 bytes generally. Since TCP packets cannot be fragmented (according to DF flag in the IP header of the packets defined in the protocol), they will be discarded. As a result, Internet access slows down. Modify the TCP MSS value to enable the router to join in the MSS value negotiation process, and therefore avoid packet discarding during TCP transmission.
The Dialer interface is a virtual service bearing interface of devices, and it is invisible on the device panel. This interface is snooping up, which causes switchover failures if the router attempts to switch over to a normal physical interface after dialup fails. Run the dialer number 1 autodial command to ensure that the state of the interface is Down after dialup fails and the route to the Dialer interface is canceled. Then, link switchover can be implemented.

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