All existing domain names of sites can be classified by level. The most common level is the second. A typical example of such a domain is site.com. In this case, the first level is the direct name of the site, and the second is the domain zone, which is separated from the name by a dot.You can also consult with seo consultant.
As a rule, all more or less serious sites (designed for active development and monetization) are placed on such domains. There are several reasons for this – a short URL (useful from the SEO and memorability point of view), more possibilities in terms of the functionality used, the absence of any restrictions (advertising, file upload, internal website policy, etc.).
As for the domains of the third and lower levels, they are much less priority. Such names, along with the domain zone, appear so-called subdomains – prefixes, separated by a dot from the rest of the name. A typical example of a third-level domain is forum.site.ru.
In this case, it is implied that the site hosted on the second-level domain contains a forum with a third-level name. Purely theoretically there can be a lot of levels – here everything is limited only by the maximum length of the entire name (255 characters). However, it is not always advisable to make long multi-level names (again, due to problems with indexing, SEO, memorability, etc.).
However, sometimes there are situations in which it is possible to include a section on the third level domain in the site. Below we list these situations.
1. MANAGEMENT OF THE SITE
Strict division of responsibility between administrators or moderators of the site. As a rule, this problem is solved by creating several user groups in the admin panel. However, a section hosted on a lower level domain is, in fact, a separate site, so no additional groups can be created here.
2. OTHER SEARCHING REQUESTS (SEMANTICS)
Optimization of the section for non-thematic keys to the main site. If there is a forum, the subject of which differs from the subject of the main resource, then when searching for promotion, problems of compatibility of key phrases and words may arise – irrelevant keys from the forum will underestimate the positions of the main site and vice versa.
In order to prevent this, you can place this forum on a third-level domain.
3. Different CMS
Using different software systems when creating a site. For example, the main resource is created on one CMS, and one of the sections on the other. It will be much easier to create two sites, and then one of them (secondary) will be placed on the third level domain.
4. VERSION FOR TESTING NEW FUNCTIONAL
Testing software modules. Some new modules and plug-ins are regularly added to some sites, which must be properly tested before the final launch. Testing on the main site is fraught with consequences (site failure, online deterioration, behavioral factors, etc.).
Therefore, you can make a test section and place it on a third-level domain.
5. INSPECTION OF HYPOTHESIS
Experiments with design and A / B testing. Here, everything is similar to the previous item (the experiment is conducted in the test section on the third level domain).
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