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Subdomains & Google

Truth about subdomains



3:01 am on Jan 31, 2007 (gmt 0)

5+ Year Member

I have been reading all day about sub domains advantages and disadvantages. Can some one tell me the truth? Is it ok to use sub domain? For example my site is about homes, and I want to create sub domain using brand names, size, cost, and so. I want the site to pretty much look the same but each sub domain targets keywords for that category, is that ok? Can you interlink each sub domain? What about sharing images all from the main domain? Someone please help



4:18 am on Jan 31, 2007 (gmt 0)

WebmasterWorld Senior Member tedster is a WebmasterWorld Top Contributor of All Time 10+ Year Member

It's quite OK to use subdomains, but using them merely to probe for a ranking advantage of some kind is likely to create trouble, sooner or later -- if for no other reason than early success could tempt you to push the envelope even further.

But there are other reasons. In many ways, a subdomain will be treated as a separate domain and will need to establish its own trust signals. My advice is to use subdomains only when the content involved serves a subtantial and distinct business purpose -- to the degree that you might also at least consider using a separate domain name for the purpose.

[edited by: tedster at 5:32 am (utc) on Jan. 31, 2007]


5:10 am on Jan 31, 2007 (gmt 0)

5+ Year Member

Just a thought – in addition to what was already said you can also use subdomains to speed up your page load time, especially if page(s) are image, script, etc intensive. For example, load content from www.example.com, images from images.example.com, css from css.example.com. User’s browser will simultaneously (well, in parallel) open connections to all three subdomains, your page will load faster, your users will be happier,….

[edited by: Tastatura at 5:10 am (utc) on Jan. 31, 2007]


5:08 pm on Jan 31, 2007 (gmt 0)

10+ Year Member

I don't think there is any technical basis to support the idea that subdomains load faster than internal pages, in fact, its just the opposite.

For every domain or subdomain you reference in a document your browser has to do an additional DNS lookup to find the IP for that server. This adds round-trip time to the lookup and actually makes the page load slower.

This only relates to the first lookup however, after that its cached and doesnt take anymore time at all. For the best possible optimization you would put all your images and scripts under the www domain and reference them with a full url.

In regard to the initial post, if you create a separate subdomain for every listing you will most certainly get banned from Yahoo and probably google also. Your better off to keep a good ratio of internal pages - subdomains.

I would say just as a rulew of thumb in my experience, try to keep a minimum of 10 pages for every subdomain. (or under every sub-domain)
- once you get over 100 a subdomain is probably a positive move.



6:20 pm on Jan 31, 2007 (gmt 0)

5+ Year Member

I realize that my prewious answer to the original question about subdomains was a bit “off” - the poster was primerly concerned about using subdomains for branding, and I only responded with possible technical usage of subdomains because of the next to last sentence regarding serving images. So no thread hijacking here but

I don't think there is any technical basis to support the idea that subdomains load faster than internal pages, in fact, its just the opposite.

In a nutshell, and ignoring for a moment differences between HTTP 1.0 and HTTP 1.1, as well as difference between browsers – browsers, by default, restrict two connections per host. So if your site uses one host, all requests are forced to use two connections. It means that all of the content, images, and other objects are forced two use only two connections. Now picture a page with a lot of images (image gallery) – all of the requests for those objects will go through two connections. Idea behind multiple subdomains is to “spread” that load and allow for more then two connections. If you create CNAMEs for each subdomain, you can “trick” the browser into thinking that it is connecting to multiple servers, so if you have images1.example.com and images2.example.com and image3.example.com you would get 6 connections (vs 2) and that would increase your page load time. Note that I am not talking about improved load time for page where you have a little bit of text and nothing else, but rather page which has a lot of objects.

To post a link or not to post a link...the link is to an interesting study so mods might let it fly - One of the Google's engineers did a study relevant to this subject - Optimizing Page Load Time [die.net]

[edited by: Tastatura at 6:31 pm (utc) on Jan. 31, 2007]


7:13 pm on Jan 31, 2007 (gmt 0)

10+ Year Member


Wow, I had no idea that browsers defaulted to 2 connections per hostname! That obviously makes my earlier post obsolete. Thanks for the info, im off to create some cnames :)


8:09 pm on Jan 31, 2007 (gmt 0)

WebmasterWorld Senior Member 10+ Year Member

if you create subdomains google will list multiple versions of your site which is obviously a good thing. For example in one sector google is listing one particular scraper 4 to 12 times over 2 or 3 pages just because they split their pages into subs.


9:22 pm on Jan 31, 2007 (gmt 0)

10+ Year Member

Subdomains are fine. I've been using em for 4-5 years now with very good results.

I think the advice about making sure there is substantial content in them is spot on.

If you created a bunch of 1 page subdomains, that would be dodgy. Would it get you in trouble? I don't know if it would now, but probably eventually...


1:01 am on Feb 1, 2007 (gmt 0)

WebmasterWorld Senior Member 10+ Year Member

I would consider myself somewhat of an expert on the subject of subdomains and I consider myself an expert in only a few areas.

Google considers a subdomain as individual site, for the most part.

The subdomain is unaffected from influence of the top level domain, UNLESS the top level domain links to the subdomain in a prominent manner. [ I.E. About.com ]

When the top level domain links to the subdomain, the subdomain carries the same weight as any page on the top level domain.

If the subdomain is totally separated for the top level domain, its weight is measure by the links pointing directly to the subdomain. [I.E. Blog Hosting Accounts]

As usuall, keywords within the subdomain's name effects rankings.

I hope this made sense.


7:46 pm on Feb 1, 2007 (gmt 0)

5+ Year Member

Minnapple in your opinion do you think it is a good ideal to have the main domain point to the sub-domain? What about having the sub-domains point to the main domain? When you say prominent manner, what do you consider prominent? My plan was to use a left border with a list of text link categories on the main domain and for each text link have it point to the sub-domain matching that category, and do the same thing on each sub-domain? Or should I keep the sub-domains completely separated and work link popularity on each sub-domain. Each sub-domain is going to be its own category. I hope I did not confuse you…thanks for all the help.


8:12 pm on Feb 1, 2007 (gmt 0)

5+ Year Member

Just wanted to say thanks to everyones help

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