4 ms·

':' is also a perfectly valid character in a domain name, so the naive splitting already does not work in the IPv4 ecosystem.

tatersolid 8y ago
No, a colon is not legal in a domain name or host name. See RFC 1123. Only alphanumerics and the hyphen character are allowed in DNS labels, which are separated by full-stop characters. Non-hostnames in DNS may also allow the underscore character as part of a DNS label.
- peanut-walrus 8y ago
  RFC 1123 specifies the preferred format, not what is mandatory. This is clarified in RFC 2181: "The DNS itself places only one restriction on the particular labels that can be used to identify resource records. That one restriction relates to the length of the label and the full name. The length of any one label is limited to between 1 and 63 octets. A full domain name is limited to 255 octets (including the separators). The zero length full name is defined as representing the root of the DNS tree, and is typically written and displayed as ".". Those restrictions aside, any binary string whatever can be used as the label of any resource record. Similarly, any binary string can serve as the value of any record that includes a domain name as some or all of its value (SOA, NS, MX, PTR, CNAME, and any others that may be added). Implementations of the DNS protocols must not place any restrictions on the labels that can be used." You are correct that it can not be used in a hostname and I am not sure how it should be encoded when used in a URI, but for a domain name it is perfectly valid. Indeed, I tested this on my local DNS server running Knot and I can create a domain name with colons in it and it also resolves using dig.
  - tatersolid 8y ago
    I can’t register “foo:bar.com” on Hover, GoDaddy, or anywhere else. There’s a difference between how DNS software is supposed to treat label data as opaque octet strings for forward-compatibility reasons, versus the standards for valid host and domain names enforced by the rest of the Internet standards.

tatersolid 8y ago

No, a colon is not legal in a domain name or host name. See RFC 1123. Only alphanumerics and the hyphen character are allowed in DNS labels, which are separated by full-stop characters. Non-hostnames in DNS may also allow the underscore character as part of a DNS label.

peanut-walrus 8y ago
RFC 1123 specifies the preferred format, not what is mandatory. This is clarified in RFC 2181: "The DNS itself places only one restriction on the particular labels that can be used to identify resource records. That one restriction relates to the length of the label and the full name. The length of any one label is limited to between 1 and 63 octets. A full domain name is limited to 255 octets (including the separators). The zero length full name is defined as representing the root of the DNS tree, and is typically written and displayed as ".". Those restrictions aside, any binary string whatever can be used as the label of any resource record. Similarly, any binary string can serve as the value of any record that includes a domain name as some or all of its value (SOA, NS, MX, PTR, CNAME, and any others that may be added). Implementations of the DNS protocols must not place any restrictions on the labels that can be used." You are correct that it can not be used in a hostname and I am not sure how it should be encoded when used in a URI, but for a domain name it is perfectly valid. Indeed, I tested this on my local DNS server running Knot and I can create a domain name with colons in it and it also resolves using dig.
- tatersolid 8y ago
  I can’t register “foo:bar.com” on Hover, GoDaddy, or anywhere else. There’s a difference between how DNS software is supposed to treat label data as opaque octet strings for forward-compatibility reasons, versus the standards for valid host and domain names enforced by the rest of the Internet standards.