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					                                         Re: www Needed in URL?

Re: www Needed in URL?

Source: http://sci.tech−archive.net/Archive/sci.electronics.design/2008−07/msg04333.html



      • From: Jeff Liebermann <jeffl@xxxxxxxxxx>
      • Date: Sun, 27 Jul 2008 15:37:55 −0700

On Sun, 27 Jul 2008 14:43:53 −0700 (PDT), mpm <mpmillard@xxxxxxx>
wrote:


        OMG, my head is going to explode!


Put a plastic bag over your head. It will contain the explosion and
make cleanup somewhat easier.


        microsoft.com and www.microsoft.com
        Are they the same thing, or are they different?


Different.
www.microsoft.com is a FQDN (fully qualified domain name). The three
parts shown are:
com The TLD (top level domain).
microsoft The domain.
www The server, hose, or machine.
In order to specify a FQDN, you need all three.

If you only specifiy microsoft.com, that's only the domain and can
refer to any of Microsoft's servers.

However, many DNS servers are configured to redirect calls to the
domain, to a specific server. That's why just microsoft.com works.
For example:

C:\>nslookup
Default Server: DD−WRT
Address: 192.168.1.1


        microsoft.com

Server: DD−WRT
Address: 192.168.1.1


Re: www Needed in URL?                                                                     1
                                        Re: www Needed in URL?


Non−authoritative answer:
Name: microsoft.com
Addresses: 207.46.197.32, 207.46.232.182


        www.microsoft.com

Server: DD−WRT
Address: 192.168.1.1

Non−authoritative answer:
Name: lb1.www.ms.akadns.net
Addresses: 65.55.21.250, 207.46.19.190, 207.46.19.254, 207.46.192.254
207.46.193.254
Aliases: www.microsoft.com, toggle.www.ms.akadns.net
g.www.ms.akadns.net

Note that the lookup points to the Akamai DNS redirectors.
<http://news.cnet.com/2100−1001−251686.html>
You picked a rather bad example becuase MS uses a load balancing
system, where the DNS (domain name service) redirects lookups of
www.microsoft.com to a localized pool of available servers to avoid
overloading any particular server.


        Can one always take you to destination−A, and the other always to
        destination−B?


No. With load balancing and DNS redirection, the decision is not
yours. You can select a specific server ONLY by IP address, not name.


        Can they be owned by different entities?


No. All sub−domains and server names under microsoft.com are owned by
whomever owns microsoft.com. You can delegate ownership and control
of subdomains, as is common in the geographic domains, such as .US,
but I doubt that Microsoft will tolerate that. For example, my office
FQDN server is comix.comix.santa−cruz.ca.us. The US domain is owned
by Network Solutions. The .ca.us domain is also run by them.
santa−cruz.ca.us is run by chime.com. I own the sub−domain of
comix.santa−cruz.ca.us. The gateway server is non−cleverly named
comix.comix.santa−cruz.ca.us. There's also
smtp.comix.santa−cruz.ca.us and www.comix.santa−cruz.ca.us, but
they're local only in my office.


        How would a DNS resolve this?

Re: www Needed in URL?                                                      2
                                      Re: www Needed in URL?


How DNS redirection works:
<http://www.cse.iitk.ac.in/users/braman/courses/cs625−fall2003/lec−notes/lec−notes30−1.html>
Note that there are various algorithms to impliment load balancing. In
most case, the DNS server will do a reverse DNS lookup on your IP
address, determine the approximate geographic location, and assign the
"nearest" web server to the DNS lookup for www.microsoft.com.

Note that DNS redirection is NOT required to perform load balancing.
It can be done by the router:
<http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094820.shtml>

How DNS works:
<http://www.howstuffworks.com/dns.htm>
<http://www.faqs.org/docs/linux_network/x−087−2−resolv.howdnsworks.html>
<http://technet2.microsoft.com/windowsserver/en/library/19a63021−cc53−4ded−a7a3−abaf82e7fb7c1033.mspx?mfr=t

−−
Jeff Liebermann jeffl@xxxxxxxxxx
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831−336−2558
.




Re: www Needed in URL?                                                                            3

				
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