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[tech] IPv6 addresses in URLs

Alex // nytpu alex at nytpu.com

Thu Apr 15 19:38:43 BST 2021

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On 2021-04-15 08:07PM, almaember wrote:

Please excuse my lack of knowledge about SNI, but can't clients send

the IP address as a host too?RFC-6066 mandates the use of fully qualified domain names, but says:

...Currently, the only server names supported are DNS hostnames;

however, this does not imply any dependency of TLS on DNS, and other

name types may be added in the future...

It also says:

Literal IPv4 and IPv6 addresses are not permitted in "HostName".https://tools.ietf.org/html/rfc6066#section-3

TLS 1.3 simply says that it's mandatory to implement SNI as specified inRFC6066 §3, so unfortunately no updates therehttps://tools.ietf.org/html/rfc8446#section-9.2

However, right before sending this, I realized that there's a key point that Ididn't realize until reading the spec just now: the HostName field can be 0characters. TLS 1.3 (and Gemini over TLS 1.2) mandates that the SNI extension/exists/ in the ClientHello, but the hostname field itself can be empty,indicating to use some "default" at the operators discresion. If anyone has agitlab account, this might be a good thing to open an issue to clarify.

~nytpu

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