How Does robots.txt Behave on Domains and Subdomains?

Jun 18, 2007 - 9:36 am 0 by

In a Google Groups thread, a member has set up a subdomain on a domain and has duplicate content on the main domain:

in a nutshell, domainB.domainA.com and domainB.com is pointing to the same content

To avoid duplicate content issues, he's looking for a way to implement the robots.txt file so that the subdomain (domainB.domainA.com) is not indexed by Google, but that the main domain itself (domainA.com) is still indexed.

Bergy, one of Google's newest Webmaster Central representatives, offers some insights.

When a spider finds a URL, it takes the whole domain name (everything between 'http://' and the next '/'), then sticks a '/robots.txt' on the end of it and looks for that file. If that file exists, then the spider should read it to see where it is allowed to crawl.

In your case, Googlebot, or any other spider, should try to access three URLs: domainA.com/robots.txt, domainB.domainA.com/robots.txt, and domainB.com/robots.txt. The rules in each are treated as separate, so disallowing robots from domainA.com/ should result in domainA.com/ being removed from search results while domainB.domainA.com/ remains unaffected, which does not sound like not something you want.

When in doubt, Bergy suggests that you use the Google robots.txt Analysis Tool to see if robots.txt is doing what the webmasters would typically expect.

Forum discussion continues at Google Groups.

 

Popular Categories

The Pulse of the search community

Search Video Recaps

 
Video Details More Videos Subscribe to Videos

Most Recent Articles

Google Ads

Confirmed: Google Ads Errors & High Latency Issues

Jul 2, 2025 - 7:55 pm
Search Forum Recap

Daily Search Forum Recap: July 2, 2025

Jul 2, 2025 - 10:00 am
Google Updates

Google June 2025 Core Update Volatility Just Began - Do You See It?

Jul 2, 2025 - 8:35 am
Google Search Engine Optimization

July 2025 Google Webmaster Report

Jul 2, 2025 - 7:51 am
Google Search Engine Optimization

Google On Links & Core Updates

Jul 2, 2025 - 7:41 am
Bing Search

Bing Places Copilot Search As First Tab & Replaces All With Web

Jul 2, 2025 - 7:31 am
Previous Story: What's the Best Format to Name Images for Search Engines?