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Say I have two domains, foo.com and bar.com, and I initially have an A record for:

www.foo.com → 1.2.3.4

I then decide I want www.bar.com to resolve to this IP, so I delete www.foo.com's A record, and add an A record for bar:

www.bar.com → 1.2.3.4

This looks fine via dig. However, when I do a reverse DNS lookup on that IP, I still see www.foo.com.

Any idea how long reverse DNS takes to propagate?

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DNS does NOT propagate! Records are cached, the TTL controls the caching. cache!=propagation –  Zoredache Aug 24 '11 at 20:35
    
fair enough. i think you get my point though. –  Joe batista Aug 24 '11 at 20:40

2 Answers 2

up vote 1 down vote accepted

Propagation depends on the TTL set for the DNS hosts involved and may also be hindered by local caching on your client. Also, depending on how you're making your changes, you may have to independently enter the reverse entry.

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Most of the time you need to do an RDNS entry manually, or have whoever hosts the DNS to do it. –  MaQleod Aug 24 '11 at 20:11
    
Thanks -- the TTL on the original entries were 3600, so after >24 hours I would have expected it to be fully expired. I'm using Amazon route 53 for DNS, I'll look to see if they have a way to edit RDNS entries. –  Joe batista Aug 24 '11 at 20:16
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-1 DNS does not propagate. –  Zoredache Aug 24 '11 at 20:36

This is nothing to do with the mythical idea of "DNS propagation". As Zoredache has quite rightly said, this is an erroneous concept (based, if it is based upon anything at all, upon the long-since-altered behaviour of some domain name registries). The DNS does not work that way. Your data were available from your content DNS servers to the world as soon as you entered them.

This is everything to do with the fact that you have name→address conflated with address→name. You've entered a name→address mapping but you've expected that to magically affect the lookup of an address→name mapping. You're spending days at a time waiting for things to "propagate" when you haven't in fact enacted any changes to the relevant data in the first place.

If you want to look up the new name→address mapping that you've just entered, look up the domain name. If you want to change what an address→name lookup returns, change the address→name mapping data in your database. Address→name mappings do not involve either A or AAAA resource record sets.

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