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This seems exactly backwards, though. “testserver4.mycorp.example” (no trailing dot) is not fully-qualified and as such could refer to any number of things of

This seems exactly backwards, though. “testserver4.mycorp.example” (no trailing dot) is not fully-qualified and as such could refer to any number of things of differing identities, e.g. “testserver4.mycorp.example.atthomenetwork.com”. On the other hand, “testserver4.mycorp.example.” (trailing dot) is fully-qualified and is not an ambiguous identity.

tialaramex 5y ago
Right, so under your approach they need to add a dot, every single time. This wastes a byte during the handshake, in order to transport the dot which you've decided must be there. Whereas the approach they actually shipped does not waste that byte. If it makes you more comfortable pretend it's an amazing "compression scheme" where they omit that extra byte with a dot in it to save space. See also IEEE 754 floating point where that first 1 in your binary floating point number is omitted entirely because it's implied and so writing it into the 32-bit value anyway would waste an entire order of magnitude.
foxfluff 5y ago
> “testserver4.mycorp.example” (no trailing dot) is not fully-qualified and as such could refer to any number of things of differing identities, e.g. “testserver4.mycorp.example.atthomenetwork.com”. Whether a domain is fully qualified depends on the application. There's no universal syntax. The trailing dot is merely an interface convention followed by some applications to allow the user to indicate that the domain name is complete. It's only useful for applications that don't always deal with fully qualified domains, and perhaps ones that deal with top level domains. RFC1123 6.1.4.3 Interface Abbreviation Facilities: User interfaces MAY provide a method for users to enter abbreviations for commonly-used names. [..] If an abbreviation method is provided, then: (a) There MUST be some convention for denoting that a name is already complete, so that the abbreviation method(s) are suppressed. A trailing dot is the usual method. If you add trailing dots where the dns root would be implied anyway, this could be regarded as an "over-qualified" name. It is considered an error. For example in SMTP. RFC1123 5.2.18 Common Address Formatting Errors: o Some systems over-qualify domain names by adding a trailing dot to some or all domain names in addresses or message-ids. This violates RFC-822 syntax. RFC822 says "The root node is common to all addresses; consequently, it is not referenced." Since SNI always uses fully qualified domain names, there is no purpose to having a trailing dot.

tialaramex 5y ago

Right, so under your approach they need to add a dot, every single time. This wastes a byte during the handshake, in order to transport the dot which you've decided must be there. Whereas the approach they actually shipped does not waste that byte. If it makes you more comfortable pretend it's an amazing "compression scheme" where they omit that extra byte with a dot in it to save space. See also IEEE 754 floating point where that first 1 in your binary floating point number is omitted entirely because it's implied and so writing it into the 32-bit value anyway would waste an entire order of magnitude.

foxfluff 5y ago

> “testserver4.mycorp.example” (no trailing dot) is not fully-qualified and as such could refer to any number of things of differing identities, e.g. “testserver4.mycorp.example.atthomenetwork.com”. Whether a domain is fully qualified depends on the application. There's no universal syntax. The trailing dot is merely an interface convention followed by some applications to allow the user to indicate that the domain name is complete. It's only useful for applications that don't always deal with fully qualified domains, and perhaps ones that deal with top level domains. RFC1123 6.1.4.3 Interface Abbreviation Facilities: User interfaces MAY provide a method for users to enter abbreviations for commonly-used names. [..] If an abbreviation method is provided, then: (a) There MUST be some convention for denoting that a name is already complete, so that the abbreviation method(s) are suppressed. A trailing dot is the usual method. If you add trailing dots where the dns root would be implied anyway, this could be regarded as an "over-qualified" name. It is considered an error. For example in SMTP. RFC1123 5.2.18 Common Address Formatting Errors: o Some systems over-qualify domain names by adding a trailing dot to some or all domain names in addresses or message-ids. This violates RFC-822 syntax. RFC822 says "The root node is common to all addresses; consequently, it is not referenced." Since SNI always uses fully qualified domain names, there is no purpose to having a trailing dot.