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I'm using Ubunutu 10.04 and doing whois queries on a list of domains. I've got very limited knowledge about the whois system and have some specific questions that I've found difficult to find specific answers on. I'm not even sure if this is the right place to ask the question, if its not please direct me to where I should ask it, thanks.

As far as I understand it ubuntu's whois service queries a set (or maybe 1) known whois server on port 43 for the parameter passed in. This server in turn keeps a database of whois information. I've heard of thick vs. thin whois servers where thick servers have the information locally and thin servers knowing where to get it.

Is there a rate limit to utilizing this service, and if so what is it? Is it known? Who sets it? Is it per ip address? How do "they" handle determining who the rate limit is coming from?

I'm trying to better understand the whois service and how it works.

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Is the limit build into the whois request timing itself? I notice it takes a few seconds per request. – Travis Aug 31 '10 at 9:10

The OS/Whois utility doesnt rate limit queries, however the registrars do.

IANA Delegate the control of all TLD's, in the case of .com thats delegated to VeriSign, they in turn rate limit the queries allowed - the mechanism they use to do it and the amount to which they limit however isn't public knowledge.

Almost all registry's do this to stop people continually querying domains in the hope that one of them "drops" and that they can then hijack the domain for profit.

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Many resellers provide APIs so you can continually query without using the WHOIS. A good example is OpenSRS who provide details at – Richard Holloway Aug 31 '10 at 10:24
Yeah but tucows/opensrs API results are cached ;-) and their whois server rate limits : – Geraint Jones Aug 31 '10 at 10:41
+1 @c10k: Thanks for that information. I hadn't looked into it enough. This is useful. – Richard Holloway Aug 31 '10 at 14:47

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