How important is it for DNS servers to be in different geographical locations?

DNS is designed to be a cacheing database, so as long as your TTL is set up right, latency shouldn’t be a problem.

Ah, right, since it’s propagated to all the ISPs.

Yah, I was wondering if you meant in terms of the Internet as a whole? or if you were setting up for internal WAN/LAN?

But then, “propagated to all the ISPs” kinda settled that. ;-)

@cwilbur: Longer TTL means longer propagation, right? Is 3600 more reasonable than 86400?

Longer TTL means that the response will be cached for longer. This means it will take longer to expire if you change something, and a longer window where people will get the old IP address.

A wise thing to do is to keep your TTLs low until your network is settled, because that minimizes the propagation problem, and then crank them up.

Well, “reasonable” depends on what’s going on.

From Wikipedia: Shorter TTLs can cause heavier loads on an authoritative nameserver, but can be useful when changing the address of critical services like web servers or MX records, and therefore are often lowered by the DNS administrator prior to a service being moved, in order to minimize disruptions.

As a default, you’d want longer TTL if you’re not expecting changes to your server(s)... then lower the TTL whilst in transition… ah, just like @cwilbur explained so succinctly.

@cwilbur: But the “default” TTL you set will be the minimum time to propagate, right? Say you have a DNS emergency, but a TTL of 86400. Even if you drop the TTL, that change wouldn’t get propagated until a day later, correct?

Right. The new data won’t be propagated until the old data times out.

The best solution, clearly, is to plan your emergencies a couple days in advance.