The myth of DNS “propagation” needs to die. Changed DNS entries do not “propagate”. The old cached DNS entries in DNS resolvers simply expire, in an arbitrary order. DNS resolvers are not linked geographically; there is no “propagation”.

If this tool was querying a list of widely-used public (and/or private) DNS resolvers, it might be useful. But pretending that DNS entries propagate geographically does not do anyone any favors.

> The myth of DNS “propagation” needs to die.

What's the actual issue? Are you being frustrated by people laboring under the assumption that DNS records are being sent by carrier pidgeon or something?

> There is no geographical connection whatsoever.

DNS censorship will presumably be based on geopolitical boundaries, which in turn are bound by geography. And I wouldn't be entirely suprised if poor network connections - including those potentially geographically bound (poor weather / flooding / tornados severing or degrading links or power) had some (minor, infrequent) impact on the rate stale cache entries are evicted in favor of fresh ones.

Granted, none of that means a DNS resolver halfway across the globe from the authoritative servers can't typically get updated results <200ms (≈light speed), which is safely ignorable / won't be visible as records propagating from geographic neighbor to geographic neighbor. And granted further, I'm both too boring to censor, and too smart to be on call for anything that would make me aware of global outage reports - so the map is admittedly useless to me beyond farming that hacker vibe aura.

But I imagine there's at least one or two dudes out there that'll see a red dot in, say, Australia - and that'll save them a few minutes, by giving them a shortcut to determining the root cause of some issue reported in Australia by letting them correctly guess/blame stale DNS records.

a) different DNS systems get the change out to all the authoritatives different ways. Some of them with much delay. Delays are hopefully minimal on modern systems, but I've worked with bad systems where you change dns in the api and it takes minutes and sometimes hours for the authoritatives to start returning new results; traditional notify/axfr based systems often have a queue of several seconds at least.

b) as resolver caches expire, new queries will hopefully get new answers (as long as the authoritatives get updated per a), and eventually you get the new results everywhere except for resolvers that do terrible things...

When the change is made and it takes time for the results to show up everywhere, I think propagate is a reasonable verb. You could use disperse or diffuse or something else, but you need a verb to let people know it's going to take time for your changes to be visible everywhere.

I don't know that propagate necessary implies the change becomes visible in an orderly way. 'Around the globe' doesn't really either, it's just observing from around the globe as resolvers get new data.

What verb do you prefer to use to describe how unsychronized caches obtain new values?

That's what the tool is doing - querying a bunch of public resolvers around the world to see the state of what they resolve to. Since end users usually use DNS servers close to their location, this gives an idea, around the world, of who sees what.

Agreed, this is a cache that expires and refreshes from the source DNS server. It just looks like a virus that propagates when the cache expires.

Thank you. I have this discussion all the time. The argument I get back "Right, but it seems like the change takes awhile because of the DNS cache expiring, so it's the same as propagating". My counter to that is to say "If I punch you in the mouth, would you just tell people I'd asked you be to be quiet, or would you use the right explanation as to what'd happened?"

(It's a stupid counterargument, btw, but it ends the discussion)

Ehh do you remember the defaults back in the day? And how long local vs intermediary vs backbone TTLs could be cached for, even above and beyond the set TTL?

The propagation part refers to how long it would take for all those cached requests to expire and when you could tell some random client they should be able to see the new value. Especially when you forgot to lower the TTL ahead of time.

It’s a term of art and it’s fine.

Oh that reminds me. I made a bunch of DNS changes a while ago and left all the TTLs set to 5 minutes. I should up them.

There is no such myth that I'd be aware of, and I seriously doubt the author behind this would be operating under such a misunderstanding either. Maybe you used to at some point, but then that's a separate issue.

Propagation is just an incremental spread across a topology. Doesn't need to be a physical topology whatsoever.

It may seem like this program suggests a physical propagation as far as its elevator pitch goes, but one glance at the readme clears it up pretty quickly that that's not actually the case.

Changes do propagate, and seeing funny blinking lights on a world map is cool. Doesn't mean there'd be an intent to convey the process as a geographical spread.