DNS: Why not just *always* use very short TTLs?

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df-sean

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Feb 8, 2007
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I often see the question posted in these forums and elsewhere about how to minimize the pain of transfering a site to a new server/IP address. And the answer is always to lower the TTLs to about 5 mins or 1 hour. Then after everything is stable on the new server, raise the TTLs back up to 4 hours or 24 hours or whatever.

But why? Why not just leave it very short so that in case of some unforeseen disaster sometime down the road, you can quickly point the domain somewhere else if you need to.

Is there any significant advantage to using long TTLs?
 
The longer the TTL the less the load on the internet, which transmits requests, your authoritative servers, which must answer requests, and caching nameservers, which must ask more often.

Years ago when the Internet was less robust and servers less powerful, this was an issue. It's really not anymore.

But ...

Some ISPs (AOL was infamous for this in the past; I don't know if they still do it) for replacing low TTLs with their own much higher ones.

And some (self-proclaimed?) Internet experts will complain if they find out you're doing what they consider abusing the system.

However, all that said, we use 600 as default for TTL; we've done it for at least ten years, and we haven't gotten any complaints on it for at least five years.

Jeff
 
I would agree with Jeff I dont really see an issue with using low TTLs as a permanent setting.
 
Thank for the speedy input guys. So... 600 huh? That sounds fairly reasonable.

While we're on the topic. Are there any *known* networks that will disregard these settings or "punish" you for setting them to low?

Anyone got a definitive answer about how AOL handles low TTLs these days?

In your experience, are these low TTLs respected pretty much everywhere these days?
 
No, this is not a definitive answer. It's been our experience that we've seen no complaints.

However keep in mind that your local server, router, or even your browser, may cache stale IP#s for as long as forever, if they're not restarted.

Jeff
 
I think it would be great to have a lower TTL by default (in /usr/local/directadmin/data/templates/named.db), don't you think so?
 
It doesn't really matter what I think; what matters is what the folks who consider themselves authoritative on the DNS system think; they're the ones who will or won't like what you do.

What I'd prefer is that DirectAdmin have a way to make changes to the TTL; perhaps to the entire SOA record.

Jeff
 
You can lower the TTL and the SOA here by editing the named.db file:
http://help.directadmin.com/item.php?id=87
Doing it through the interface isn't possible at the moment due to how the storage classes are currently setup.. adding the ability to edit them would require a full module rewrite. It may happen eventually, just not in the near future.

John
 
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