The extranet of the library, like other places, needs to use tunet's account, which is the one that the main building has to pay. I don't know what you mean by this extranet. If it is an off-campus domestic network, you can log in directly with your account. The charge is 1.5 per month, regardless of traffic. But if you mean the external network, you have to choose the "open (international)" item on tunet, charge according to the traffic and deduct it from the account in the main building. However, it is recommended to use Sogou browser. Access to foreign networks is free, and domestic (restricted) access is generally enough.