What is the maximum size of a DNS FQDN?

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Multiple Choice

What is the maximum size of a DNS FQDN?

Explanation:
DNS FQDN length is governed by the protocol: the total length allowed for a domain name in a DNS message is 255 octets, including the root label. Each label can be up to 63 octets, and you can have up to 127 labels (the root is included in that count). So the maximum on-the-wire size of a fully qualified domain name is 255 octets, which corresponds to 127 labels. That's why the correct choice expresses 255 as the total size and 127 as the number of labels. In textual form you often see the trailing dot to indicate the root, but the fundamental limit comes from the 255-octet cap in DNS messages. The other options don't capture both constraints: 512 is a different boundary tied to historical UDP message size, not the FQDN itself; 63 is only the per-label limit; 200 is not the defined maximum.

DNS FQDN length is governed by the protocol: the total length allowed for a domain name in a DNS message is 255 octets, including the root label. Each label can be up to 63 octets, and you can have up to 127 labels (the root is included in that count). So the maximum on-the-wire size of a fully qualified domain name is 255 octets, which corresponds to 127 labels. That's why the correct choice expresses 255 as the total size and 127 as the number of labels. In textual form you often see the trailing dot to indicate the root, but the fundamental limit comes from the 255-octet cap in DNS messages. The other options don't capture both constraints: 512 is a different boundary tied to historical UDP message size, not the FQDN itself; 63 is only the per-label limit; 200 is not the defined maximum.

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