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myyis

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DNS failover

I am thinking to use this service
http://www.dnsmadeeasy.com/services/dns-failover-system-monitoring/
There it says

"How Quickly Will My IP Change?
This is dependent on the TTL of your record as well as cache on local resolving name servers of querying clients who accessed your IP recently. Records that use DNS Failover should have a short TTL between 180-300 seconds. This will minimize the amount of time the record caches in resolving name servers decreasing the amount of time it takes for your new IP to populate when an outage occurs. Clients who have not accessed your IP recently will reach the new IP instantly thanks to DNS Made Easy’s instant IP updates. Clients who accessed the IP before the change was made will have about a 10 minute wait until the cache expires on the resolving name server and the new IP is populated."


But here says that
http://en.wikipedia.org/wiki/Time_to_live
"Newer DNS methods that are part of a DR (Disaster Recovery) system may have some records deliberately set extremely low on TTL. For example a 300 second TTL would help key records expire in 5 minutes to help ensure these records are flushed quickly worldwide. This gives administrators the ability to edit and update records in a timely manner. TTL values are "per record" and setting this value on specific records is sometimes honored automatically by all standard DNS systems worldwide. However a problem persists in that many caching DNS nameservers set their own TTLs regardless of the authoritative records, so it cannot be guaranteed that all downstream DNS servers have the new records after the TTL has expired."

My question is even with dnsmadeeasy the user will see a down site for hours. Is that right?
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Kimputer

No, you didn't read correctly. It's clearly stated, the worst case scenario is this: "Clients who accessed the IP before the change was made will have about a 10 minute wait until the cache expires on the resolving name server and the new IP is populated".
If you have everything in order (2 seperate servers on different backbones), it's about 10 minutes max.
Avatar of myyis

ASKER

But wiki says

"However a problem persists in that many caching DNS nameservers set their own TTLs regardless of the authoritative records"

If they set their own TTL's let's say 14400 they will see the server down for 4 hrs? No?
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Kimputer

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