Technical topic: why can I use dual-dial bandwidth? Will there be twice the traffic after Double dial?

Basic conditions for dual-dial:

The port speed of the line must be greater than the port speed of your account (some bandwidth is 2 m for you, and 2 m for the port above, no matter how many times you dial, all bandwidth will not increase, and ADSL can directly open the cat's page for viewing)

Why can I Double dial:

In fact, dual-dial is a vulnerability in pppoe. It uses two PPP ports and simultaneously (1 ms error) dialing. Because pppoe has a certain verification process, it is successfully set up. I will explain the Principles later.

The above is the pppoe user verification diagram. As shown in the figure, when two ports use the same user name and password for dial-up, the user name or password is verified, the radius system first checks whether the user is online? If it is online, it will be 691 directly; otherwise it will pass. Because both of our accounts are dialing at the same time, their process is the same, so they both verify to the radius system, at this time, the user is not online, so it passes.

As it turns out, if you dial three or four times at the same time, it can be successful, because when the user dial verification is successful, there is still a billing process, only after this process, the user's status is updated to the radius system (that is, it is displayed online in the system). Therefore, this vulnerability cannot be prevented currently.

Of course, some abnormal ISP may restrict dual-dial or even trigger by limiting Mac, limiting time (30*24), and port speed.

If you have any questions during dial-up, you can directly add QQ or join the group for discussion.