Option D is correct. The AAA configuration binds the domain huawei.com to the authentication scheme auth1, which uses RADIUS as the authentication mode, and to the accounting scheme acc1, which also uses RADIUS. Therefore, when a user logs in with a user name in the format hcia-datacom@huawei.com, the device parses the suffix @huawei.com, matches the domain, and applies the configured RADIUS authentication method.

Option A is false because RADIUS does support accounting, and UDP port 1813 is commonly used for that purpose. Option B is false because a separate authorization server IP is not strictly required in this context; RADIUS can carry authorization attributes together with authentication/accounting processing depending on server behavior and device configuration. Option C is false because standard RADIUS communication uses UDP, not TCP, with authentication typically on port 1812 and accounting on 1813. HCIA-Datacom teaches domain-based AAA processing as a key concept, where the user name suffix determines which authentication, authorization, and accounting policies are applied on the NAS device.