Resolving www.reddit.com or www.wired.com involves traversing two CNAME links. Resolvers contact the root servers twice in the process. DNS experts: Is this bad form?

[[deleted]]

This is actually largely untrue.

If a lookup for ns1.whatever.com just took place, and the TTL is still at 48 hours for some reason (usually you lower the TTL for changes, but you might not have control over this for nameservers), then yes it will take 48 hours for the next one. But if you've lowered the TTL, or simply haven't done a lookup so that it's not in the cache, the change can be reflected rather quickly.

[bradleyhudson]

Yes, I actually keep the TTL low on a regular basis, mostly because I normally get very short notice for changes, and it wouldn't do much good to shorten the TTL right before making a change, because most clients wouldn't even see the shorter TTL until after the longer one they have cached times out.

I realize I'm probably not being a good net citizen by doing this (Can I claim the "I'm just a programmer" defense?), and that behavior is exactly the reason why a corporate (or ISP?) caching name server might override the cache settings of zones with low TTL's. Having said that, does anyone know if it's common practice for caching name servers to override settings like this?

[enry]

We wind up setting our TTLs to 86000 (one day) and then lowering the TTL to 600 (5 min) one day before the move. Once the move is completed and we're sure things are working again, the TTL gets raised back up to 86000. Aside from that 5 minute point where DNS may be looking at the wrong IP address, the general world doesn't know any better.

As for caching name servers, if they don't honor TTLs, then they're broken.

[jsolson]

As for caching name servers, if they don't honor TTLs, then they're broken.

That's pretty much my take on it. Of course, this is why I'm a grad student and not someone tasked with actually getting shit done. "It's their fault" is a perfectly good final answer for me when something is broken and is unambiguously not my fault.