Google shared a document to help on how HTTP status codes, network and DNS errors affect Google Search. The document covers each type of code & error & shows you how Google bot & Google Search hit by it.

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Users can access this document here.

The Document says:

This page describes how different HTTP status codes, network errors, and DNS errors affect Google Search. We cover the top 20 status codes that Googlebot encountered on the web, and the most prominent network and DNS errors. More exotic status codes, such as 418 (I’m a teapot), aren’t covered. All issues mentioned on this page generate a corresponding error or warning in Search Console’s Crawl Stats report.

Here is a look what Google shows in the Document:

• Googlebot follows up to 10 redirect hops and then after 10, Google Search Console will show a a redirect error
• 301 redirects are a “strong signal” but a 302 is a “weak signal” for a redirect.
• Don’t use 401 and 403 status codes for limiting the crawl rate. The 4xx status codes, except 429, have no effect on crawl rate.
• And you have to love the teapot ? 418 code

The document is wonderful and do have a look at what you can expect from Google Search regarding HTTP status codes, DNS errors and network errors.

Here are some chatter over Twitter:

"We cover the top 20 status codes that Googlebot encountered on the web, and the most prominent network and DNS errors."

— Gary 鯨理／경리 Illyes (@methode) June 26, 2021

I feel like we've been pretty clear for quite some time that the difference is minimal if at all — and that there's no value in switching from 404 to 410. Now I wonder what else we're suggesting is minimal but which folks are over-indexing on in the name of "optimization"…

— ? John ? (@JohnMu) June 27, 2021

The arguments I find useful are that a 410 is "technically correct" in many cases, and that it's easier to separate 410 from 404 in log files. IMO both are good arguments for using 410 & 404; they're non-SEO arguments, but not everything has to be SEO.

— ? John ? (@JohnMu) June 27, 2021

For urgent individual URLs, use the removal tool. For everything else, just let it crawl & drop naturally. If you remove 100k URLs, I doubt a 404 vs a 410 will be noticable for the rest of the site's visibility, even in a best-case scenario. If they're already gone, gone is gone.

— ? John ? (@JohnMu) June 27, 2021