David1978
asked on
Why do sites usually set a low TTL?
Hello!
I've checked about a dozen of web sites and I've noticed that most of them use a low TTL value in their SOA record.
Usually it's up to 1 hour. I set for my site 1 week (604800 sec.) .
So my question is... why for normal operation do sites set such low TTL values? What's the advantage? I can only see disadvantages here. More traffic, latency, more load on the servers. But maybe I'm wrong... Maybe there's something I don't know about the issue?
I've checked about a dozen of web sites and I've noticed that most of them use a low TTL value in their SOA record.
Usually it's up to 1 hour. I set for my site 1 week (604800 sec.) .
So my question is... why for normal operation do sites set such low TTL values? What's the advantage? I can only see disadvantages here. More traffic, latency, more load on the servers. But maybe I'm wrong... Maybe there's something I don't know about the issue?
Simple as it: Load balancing. And faster chance to change DNS records if necessary. e.g. if one IP gots DDoSed. Remove it and put another server on on another subnet/provider.
SOLUTION
membership
This solution is only available to members.
To access this solution, you must be a member of Experts Exchange.
ASKER
Thank you both for your replies!
I didn't quite understand, so let me clarify couple of things here.
andreas, as per load balancing. Under normal operation, what does it mean exactly? Let's say we have a few PC's which share the traffic load. So how is it different vs. just one PC. Frankly, I don't see any difference in the context of TTL.
Malmensa, you mentioned that ISP's often simply ignore the low TTL values. They probably do that to save their resources. That's understandable. Most people use their ISP's DNS servers, not their owns. But:
a) that would mean DNS issues for their customers once in a while;
b) how technically it's possible, say on BIND9 (if you know)? I know that TTL is defined in a zone file which resides on authoritative DNS server, not the ISP's. What, there's a way to "overwrite" it somehow?
I didn't quite understand, so let me clarify couple of things here.
andreas, as per load balancing. Under normal operation, what does it mean exactly? Let's say we have a few PC's which share the traffic load. So how is it different vs. just one PC. Frankly, I don't see any difference in the context of TTL.
Malmensa, you mentioned that ISP's often simply ignore the low TTL values. They probably do that to save their resources. That's understandable. Most people use their ISP's DNS servers, not their owns. But:
a) that would mean DNS issues for their customers once in a while;
b) how technically it's possible, say on BIND9 (if you know)? I know that TTL is defined in a zone file which resides on authoritative DNS server, not the ISP's. What, there's a way to "overwrite" it somehow?
SOLUTION
membership
This solution is only available to members.
To access this solution, you must be a member of Experts Exchange.
ASKER CERTIFIED SOLUTION
membership
This solution is only available to members.
To access this solution, you must be a member of Experts Exchange.