ACtE08 · Chapter 8Demo2 · Set 2🏛️ Past Licensure QuestionID: ac7df5cb
According to DNS specifications (RFC 1035 and RFC 1123), what is the maximum permissible total length of a Fully Qualified Domain Name (FQDN) or hostname?
According to DNS specifications (RFC 1035 and RFC 1123), what is the maximum permissible total length of a Fully Qualified Domain Name (FQDN) or hostname?
Multiple Choice Options
- A✓ Correct Option
255 octets
- B
256 octets
- C
125 octets
- D
128 octets
Detailed Technical Solution & Explanation
Under internet standards specified in RFC 1035 (Section 2.3.4) and RFC 1123 (Section 6.1.3.5):
•
The total length of a Fully Qualified Domain Name (FQDN / hostname) can be up to 255 octets (bytes), including label length bytes and the trailing null root octet.
•
Each individual label (subdomain component separated by dots) is limited to a maximum length of 63 octets.
Option Analysis:
•
Option A (255 octets): Correct; the maximum legal length for an FQDN is 255 octets.
•
Option B (256 octets): Incorrect; often confused with 8-bit limits, but DNS reserves one length byte limiting the wire representation to 255.
•
Option C (125 octets): Incorrect; arbitrary value.
•
Option D (128 octets): Incorrect; arbitrary value.
Reference: Demo2 · Set 2NEC Licensure Syllabus