Which statement about blocking NetBIOS traffic on a firewall is true?

• A. Blocking ports 53, 67, and 389 prevents NetBIOS traffic.
• B. Blocking ports 22, 80, and 443 prevents NetBIOS traffic.
• C. Blocking ports 80, 443, and 8080 prevents NetBIOS traffic.
• D. Blocking ports 135, 139, and 445 prevents NetBIOS traffic.

Answer: (D)

Blocking NetBIOS traffic focuses on the channels Windows uses for NetBIOS/SMB communications. NetBIOS over TCP/IP relies on specific ports to establish and carry its sessions, with 139 being the NetBIOS Session Service you’d see used for NetBIOS communications, and 445 carrying SMB over TCP/IP for file sharing and related services. The RPC Endpoint Mapper on port 135 is involved in locating and starting services that enable those network connections. Blocking these three ports blocks the essential pathways NetBIOS/SMB traffic uses to operate, effectively preventing NetBIOS communications across the network. Ports listed in other options correspond to DNS, DHCP, SSH, or web traffic and do not block NetBIOS channel paths, so they don’t achieve the same result.