Hi Jon,
An analogy... let's say you decided to move from your current
residence, and you wanted all of your mail to come to the new house.
You have two alternatives:
1) Tell all of your friends that you've moved, and they should use the
new address.
2) Tell the post office your new address, and have them redirect all of
your mail to the new place.
Well, at first, #1 might seem like a hassle. After all, it takes time
to reach all of your friends/contacts. How do you even figure out all
of the different places that have your address, in order to contact them
and get them changed properly? In other words, it takes time to propagate.
#2 is much easier. Set it up once, and presto, the problem is solved.
Only problem is, mail delivery is slower because the mail is delivered
to the wrong post office at first, and then the post office has to find
the mail that's for you and redirect it. Worse, they'll only do this
for a limited time... imagine the nightmare it would create for the
post office employees if they had to keep track of everyone who ever
moved in all of history... they _have_ to impose a limit, or it'd be
impossible to manage.
Also, there's a more basic problem with leaving a "forwarding address"
at the post office. Your address might be used by someone for something
that's *not* mail. Maybe UPS. Maybe a friend stopping by!
The analogy holds true for DNS vs. URL redirect. When you change DNS,
you have to wait for everyone's DNS cache to expire so they'll go back
to _your_ server to get a new address... this "propagation" delay might
be unpleasant for a short while. But once it's done, it's done...
people come to your new site, and all is well. (And, frankly, it's not
nearly as difficult as getting all of your contacts to use your new
mailing address!)
By contrast, a URL redirect requires someone to connect to the OLD HTTP
server first, that server then gives them a new URL, and sends them to
the new server. That's twice as many connections, so it's slower. And
that old server, like the post office, would have to keep track of your
old and new URLs "forever", which might not be practical to manage.
(Depending on the circumstance, I guess.)
Furthermore, a URL direct is part of HTTP, and will only work for HTTP
requests. It won't help you with E-mail, FTP, Telnet, SSH, or any of
the other ways of contacting your site.
So a URL redirect makes sense as a temporary measure while DNS is
propagating, but it makes no sense in the long run... (Unless i've
completely misunderstood your scenario, which is probably likely.)
On 12/2/2010 2:43 PM, Jon Paris wrote:
Question for all you web gurus out there.
What is the difference in effect between using URL forwarding and a
CNAME DNS entry?
Is it simply that URL forwarding doesn't have to propagate but CNAME
does?
Jon Paris
www.Partner400.com
www.SystemiDeveloper.com
midrange.com
