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if I want to querey the DNS delegation "manually", I normally start using one of the "DNS-Root-Servers", like b.root-servers.net.

dig @b.root-servers.net test.com

But what if the root servers would change? My question is, is there any possibility to query a "central Server" even being "above" the root servers that returns me the list of Root servers?

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2 Answers 2

up vote 6 down vote accepted

You can 'dig @b.root-servers.net . ns' to get updated root hints (which you should do periodically). Every root DNS server can return the root hints, so as long as all the root servers don't change at once you can always get updates re: those that have changed from those that have not.

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thanks very much!! was not aware of your tip, never did this before but its a great learning and solution. thanks! –  jens Jun 17 '10 at 12:30

The authoritative copy of the root hints file is at:

ftp://ftp.internic.net/domain/named.root

This lists all of the root servers, and includes all relevant A and AAAA records.

Note that Evan's dig @a.root-servers.net . ns is not guaranteed to retrieve all of the records - by default the response is truncated at 512 bytes so some will be missed. You have to add +bufsize=4096 to the dig flags to get the full data, or use a TCP connection (+tcp) instead.

EDIT: BTW, the root zone was actually just updated (17/06/2010). The "I" root server gained an IPv6 address.

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That's always been the way I've been taught to do it. With the addition that you probably don't actually need to do this, you should almost always use an upstream DNS provider instead of the root servers. –  kaerast Jun 17 '10 at 12:55
    
And we should add that the question is assuming that you're on the normal IPv4 "internet" not the thing they use in china or iran or the NSA, which likely has a different list of root servers. –  chris Jun 17 '10 at 13:05
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From my personal experience in China, this is not true, they use the same root servers as everyone (with additional tricks in the resolvers and the middleboxes). –  bortzmeyer Jun 18 '10 at 15:16

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