HP World - Demystifying DNS

[Sundar_7]

I just have a quick question here on a HP World 2004 document

ftp://198.151.251.239/pub/conference/hpworld2004/presentations04/3025.pdf

May be somebody can help me understand Page 34 in the document.

The author is trying to explain how DNS requests are resolved. I see something contradicting to my understanding of how DNS works.

PC is looking to resolve www.novell.ca (First of all, it should NOT BE http://www.novell.ca, it should be just www.novell.ca ??!?). The local DNS server is forwarding the request to ISP's DNS server. Now the ISP DNS server is contacting the TLD for the .ca domain.

Here is the thing. Document says TLD itself will return the IP address of www.novell.ca. My understanding is that, ISP DNS server will be returned the Primary DNS server IP address of novell.ca, which in turn should be queried for the www.novell.ca IP address.

I don’t believe name caching will come in to the picture here.

any useful inputs/comments will be appreciated with bunnies :-)

[Steven E. Protter]

I'm going to give this a shot because hp is probably going to edit your post and take out the url. Apparently they are not ready to have that one public.

yes the http:// part is stripped out. What goes to the dns server is the same as you'd put in a dig or nslookup command

What you get back is the numeric ip address which if the dns server is set up right lets the browser go to www.website.ca

cacheing can come into the picture though.

If there has been a recent requeset from you or another user fow website.ca then the local DNS server will in effect say, i know that and provide a faster answer without going all the way up the DNS chain toward the root servers.

I hope this helps.

SEP

[Sundar_7]

I understand caching will come in to picture if there was a recent query from my local DNS sever for the www.website.ca.

But I was referring to the scenario mentioned in the document. Document assumes www.website.ca is not in the cache and thus the ISP DNS server queries the TLD server.
I intended to say it is highly unlikely the TLD server has www.website.ca in the cache (if at all
it has some kind of caching). I agree it is reasonable to presume TLD has the DNS servers responsible for the domain website.ca in the cache.

I havenâ t got the answer for my query yet. Anyone ?

[Mark Greene_1]

"I don't believe name caching will come in to the picture here"

Sure it will. The local DNS server will first examine its name cache to see if the host is in there before even looking in its tables, let alone jumping out on the 'Net. It will then check its named.boot records to see if it's authoritative for the domain. In thise case we presume not, so then it looks in its seed cache for likely suspects to query to find out what server is the TLD for the domain in question.

You can test this yourseft. Point your browser at, say, espn.com. Then on a unix box, nslookup espn.com. You should get a non-authoritative answer, because it was resolved from the local cache (assuming the Unix box and your browser are feeding from the same local DNS server).

If you have a system where you can run 'dig" (i.e., any linux box), you'll get much more helpful and complete info.

Running dig for monnaiedeparis.com. (the French Mint's website, not likely to be in your local DNS cache), we see this:

$ dig monnaiedeparis.com.

; <<>> DiG 9.2.1 <<>> monnaiedeparis.com.
;; global options: printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 15174
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 0

;; QUESTION SECTION:
;monnaiedeparis.com. IN A

;; AUTHORITY SECTION:
monnaiedeparis.com. 6298 IN SOA ns.easynet.fr. hostmaster.easynet.fr. 2003112001 3600 1800 2419200 7200

;; Query time: 28 msec
;; SERVER: 198.212.0.242#53(198.212.0.242)
;; WHEN: Thu Sep 23 12:16:58 2004
;; MSG SIZE rcvd: 96

If we thend dig on the server that gave us the answer, we see it is indeed a TLD server and not the Primary DNS for monnaiedeparis.com:

]$ dig 198.212.0.242

; <<>> DiG 9.2.1 <<>> 198.212.0.242
;; global options: printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: 57011
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 0

;; QUESTION SECTION:
;198.212.0.242. IN A

;; AUTHORITY SECTION:
. 10800 IN SOA a.root-servers.net. nstld.verisign-grs.com. 2004092300 1800 900 604800 86400

;; Query time: 111 msec
;; SERVER: 198.212.0.242#53(198.212.0.242)
;; WHEN: Thu Sep 23 12:23:05 2004
;; MSG SIZE rcvd: 106


But whether the anser came from cache or the table, I cannot tell.

mark

[Rgomes]

I guess, here both 'recursive' and non-recursive' name resolution should come in the picture, too.

regards,
Richard

[Sridhar Bhaskarla]

Sundar,

I assume you are talking about a scenario where there is no cached entry for host.domain.root anywhere.

In theory, if the 'caching' is taken out from the picture, even it is my understanding that TLD returns the IP address of novell.ca but not the IP addresses of the machines under that domain. The intended function of LTDs is not to keep track of every machine down below it's tree. It has to work in hierarchial way.

I think author might have generalized it.

-Sri