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Comment by xg15 | Hacker News Reader

> Instead, very rudely, some resolvers will ignore your TTL and just cache your record for as long as you feel like! Like 24 hours!

Kinda surprised to hear about this one. Wouldn't this instantly break DynDNS domains that rely on short TTLs so they can keep the server's IP address in sync?

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This is more common than you might think. I have encountered cheap home routers that have dumb dns proxy caches on them that simply cache everything for a fixed time period. I heard of one that simply flushed its cache at the same time every hour.

You find out all sorts of bad DNS behavior when you run anything CDN related.

That and “ALIAS” records.

It’s way less of a problem now than it was 20 years ago (at least in the Western countries I have services in my career) but it has traditionally also been an issue for a hard cutover of services, especially for SMB and even small enterprise businesses doing things like MX cutovers.

For hard cutovers it might be a viable strategy to forward or redurect traffic inbetween changes. That is, either let the old destination forward to the new, or vice versa, then update the records to the new destination, or have an intermediary forwarding destination where you can change the destination address on an an instant and once settled move the record to that.

24h seems overly excessive but some resolvers may refuse to adhere to arbitrary low TTL and chose to answer with stale records from cache for as long as they deem necessary. 24h certainly would make many issues with that strategy very apparent.

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