The Old Joel on Software Forum: Part 4 (of 5)

fogcreek.com zone problems

I am no DNS guru at all, but note that the Expire field in the SOA record is set to the unusually low value of 3600 (usually it is within the range 86400 - 3600000), while it should be at least three times bigger than the value of the Refresh field (currently 3600).

The expire value controls how long the secondary server will cache the zone contents in the event that it cannot contact the primary server to refresh the zone. If this value is very small, then it is possible that the secondary server may stop serving the zone during an outage involving the primary server. It is probably desirable to set this value to a week or longer.

Gaspar Torriero
Tuesday, March 9, 2004

Thanks!

I got about 10 helpful suggestions during the few minutes my question was posted on the home page :) The best suggestion was to try dnsreport.com for a full list of warnings and errors, which I'll do now!

Joel Spolsky
Fog Creek Software
Tuesday, March 9, 2004

Indeed. Having an expiry & TTL set that low is going to overload your DNS server and waste lots of bandwidth.

Those DNS entrys will time out after an hour, causing the DNS servers to be queried again and again.

Unless you're planning on changing them soon, I'd set them much higher, at least a week.

Matthew Collins
Tuesday, March 9, 2004

Joel, I note you have increased the Expire values: did it help?

Gaspar Torriero
Tuesday, March 9, 2004

I fixed the TTLs and replaced the entries for dns1 and dns2 to be As instead of CNAMEs. Now dnsreport.com is reporting no errors. We'll see if the problems clear up.

Joel Spolsky
Fog Creek Software
Tuesday, March 9, 2004

Joel,

You may want to post this on your home page as well:

Whatever happened to your DNS yesterday "polluted" my DNS server (bind 9/FreeBSD). As of this morning I could still not access discuss.fogcreek.com...

... until I restarted my name server, at which point everything worked perfectly.

So, put a note on the front page stating that if people still have problems, they should restart their name servers if they are able to do so.

David Jones
Wednesday, March 10, 2004