[uug] DNS and name servers for top-level domain
jefferya at programmerq.net
Thu Apr 9 18:16:36 MDT 2009
Brent Thomson wrote:
> If you run
> dig apple.com
> you'll get a response with an authority section like this:
> ;; AUTHORITY SECTION:
> apple.com. 233959 IN NS nserver.apple.com.
> apple.com. 233959 IN NS nserver2.apple.com.
> apple.com. 233959 IN NS nserver3.apple.com.
> apple.com. 233959 IN NS nserver4.apple.com.
> apple.com. 233959 IN NS nserver.asia.apple.com.
> apple.com. 233959 IN NS nserver.euro.apple.com.
> My understanding is that the NS records for the top-level domain have to
> be stored in the root DNS servers. Does this mean that those root DNS
> servers also have the A records for looking up the IP addresses of the
> NS records in the authority section above? If not (meaning they're only
> available in Apple's DNS servers), how do you get around the
> chicken-and-egg problem of having the root servers point at the domain
> *name* of a DNS authority for a domain, but not having the A record to
> look up the address of that record?
If I'm not mistaken, this problem that you are describing is solved with
what is called a glue record. The root nameserver (or more specifically
the nameserver for the tld) should and does store the nameserver's IP
address. For example, if I ask a root nameserver about apple.com, I'm
told that I need to ask a gtld-servers.net nameserver. If I try to look
up nserver2.apple.com, which is a nameserver, and ask 220.127.116.11 which
is a tld server for .com, I get an answer section because the .com tld
nameservers store A records for nameservers.
Hopefully my tired-ness hasn't completely voided my explanation.
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