In most cases, subdomains are treated as a separate domain name. Sometimes the subdomain has the characteristics of the primary domain name. For example, in the sitelink , the subdomain may be listed at the same time as the primary domain.
Subdomains are penalized or lose weight and generally do not affect the primary domain name. But the reverse is not true, which means that if the primary domain name is punished, it will usually be affected by the subdomain.
In general, a subdomain is created on a domain with a high weight. This subdomain is similar to the new domain, and the weight must be re-established on its own.
This content is roughly the same as the way we know the search engine handles subdomains, so there is no specific introduction.
But on December 7th, when tedster was at the Las Vegas Pubcon (Webmaster’s Webmaster Conference), Matt Cutts told him that Google would soon treat subdomains as if they were subdirectories. That is to say, a maximum of two URLs under a domain name can be listed in a particular search result, and no more than three four or more subdomains will be listed in the search results at the same time as the primary domain URL.
This phenomenon is quite common. Many people open multiple subdomains in domain names with higher weights, trying to control the search ranking. Many big stations often do this.
No. 8 tedster added another sentence, saying that Matt Cutts called him to clarify in the afternoon. The change was not that the URL of a hundred percent domain name could not appear at the same time as the primary domain name. Google’s current plan is to use a damping parameter so that the third URL under the same domain name is difficult to display, and the fourth is more difficult. Matt Cutts may also talk about this issue on other occasions.
Of course, there are exceptions to this kind of treatment. For example, like a blog host, different subdomains are different bloggers and it is unlikely that they will be handled exactly like this.
I feel that if Google does this, it will have a major impact on the SEO strategies and techniques of many websites. Let us wait and see.
Update: Matt Cutts just posted a blog ,this algorithm has been in use for several weeks. No one found out.