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Re: [tech] IPv6 addresses in URLs

- Alex // nytpu <alex at nytpu.com>

@ Thu, 15 Apr 2021 12:38 -0600

Full Thread

Reply to almaember <almaember at disroot.org>

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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 in

RFC6066 §3, so unfortunately no updates there

https://tools.ietf.org/html/rfc8446#section-9.2

However, right before sending this, I realized that there's a key point that I

didn't realize until reading the spec just now: the HostName field can be 0

characters. 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 a

gitlab account, this might be a good thing to open an issue to clarify.

~nytpu

Alex // nytpu

alex@nytpu.com

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