Ingrained practices are the sort of thing that change one funeral at a time (see constant password rotation).

It's a reasonable mitigation for certain environments and does leak information that makes structuring attacks easier, but it's certainly not a hard wall of any sort. The main problem for most people is articulating the realistic threat models they are trying to address and because that rarely resolves well assuming the conversation is had at all, there is little rational pushback against "everything and the kitchen sink" approaches based on whatever blog the implementer last read.

Personally I tend to advocate assuming your attacker knows everything about you except specific protected secrets (keys, passphrases, unique physical objects) and working back from there, but that's a lot of effort for organizations where security is rarely anything but a headache for a subset of managers.

You'll see similar opinions about things like port-knocking puzzles and consumer ipv4 NAT, which provide almost zero security benefit but do greatly reduce the incidence of spurious noise in logs.

One of the examples given wasn't a server name, it was leaking potentially confidential information via the domain olympics-campaign.staging.example.org - in many environments its fine if people know project names, but NDAs are a thing, and you could end up in hot water if you accidentally leak a partnership between two companies before it's been announced.

Well, if instead of making a lot of effort in hiding your names you just didn't, you wouldn't use a name like that.

Every single person that connects to any of your networks (very likely the sandboxed mobile one too) can find that name. Basically no place hides it internally. There is very little difference between disclosing it to thousands of the people that care the most about you and disclosing it to everybody on the world.

The other examples are better. Say a never-before-seen name appears, cisco520.internal.foo.bar. Suddenly, a well-formed email appears, “Re: Cisco Support Ticket #7779311” about some additional steps to provision your new appliance. It is trivial to automate that phish by crawling the CT log.

Is this valuable enough to resist every real advancement in network security since the late 00's? Because for each one of them it's certain that people will pop-up making a lot of noise about hidden server names.

It's mostly because of them that DNS is still not reliable. Well, at least this article isn't against certificate transparency, just about how to avoid it.

I don’t think anyone is arguing that Certificate Transparency defeats “every real advancement in network security”. If you want to avoid your internal hostnames, and maybe Subject and SAN, ending up in LE, then you’re free to run your own CA.

But getting back to your parent post, maybe we can see a nontrivial real-world list of a big network to make sure it’s leaking nothing of value?

It is a perfectly valid concern. Internal domain names can contain confidential information. They become vectors for attack (especially if running vulnerable software). Obfuscation doesn't mean perfect security but it still goes a long way towards it.

I think many of us, myself included, have been conditioned to be paranoid—just because I can’t think of/don’t know of any way some data could be abused doesn’t mean I’m going to make it public.

It's mainly mitigating exposure. Some possible vulnerabilities would be social engineering(i.e. it'd be easier to send a targeted phishing URL to gain recon on an employee of a company if you know an internal domain), or injection into a public facing service that has access to internal services.

So, security through obscurity?

Security is not boolean. What’s local can be public some day. Everything should be disclosed on a need to know basis.