Comprehensive and Detailed 200 to 250 words of Explanation From HCIP Datacom Campus Network documents knowledge without any URL or Links:

In Huawei campus access authentication designs, network access is divided intopre-authentication,isolation, andpost-authenticationdomains to control user access at different stages of authentication.

Thepre-authentication domainprovides users with only the most basic network services required to initiate authentication. These services typically includeDHCPandDNS. DHCP allows unauthenticated terminals to obtain IP addresses and basic network parameters, while DNS enables domain name resolution so that users can reach authentication portals or admission servers. Therefore,DHCP and DNS servers are essential components of the pre-authentication domain, making optionsC and D correct.

AnFTP serveris a general-purpose file transfer service and is not required for user authentication. Anantivirus serverbelongs to theisolation domain, where users are redirected if authentication fails or if their devices do not meet security posture requirements, such as outdated virus signatures. These servers provide remediation resources but are not part of the pre-authentication process.

According to HCIP Datacom Campus Network documentation, limiting the pre-authentication domain to only essential services reduces security risks while ensuring successful user onboarding.