Tuesday, August 11, 2009


Security, privacy, and an inconvenience

Redirects are often discussed only in the context of search engine optimization (SEO). Here is a good example how redirects affect users as well, and why it is important to choose your redirects wisely.

The Central Intelligence Agency (CIA) in 2006 began serving its Website encrypted in an effort to improve security and privacy of the communication.

This is a clear case for a 301 redirect from the unencrypted URL http://www.cia.gov/page to the equivalent encrypted URL https://www.cia.gov/page. Instead, except for the homepage and very few other pages, all requests get redirected to a splash page informing visitors about the site changes:

CIA Site Redirect. CIA.gov has changed its Web address. CIA.gov is now encrypted, except for our Electronic Reading Room, to assure visitor confidentiality. As a result, the Web address for pages and documents in our site has changed from http:// to https://. In addition, CIA Careers has moved to a new location within the Web site. Please use the links or the search form below to find the information you seek. …

Not only is this a bad idea for search since all those links out there on various sites now transfer link weight to a splash page which is marked as non-indexable. It is also an inconvenience to users who need to navigate to the specific content or go back to the previous page and try again with an edited link.

Even the old URL for the World Factbook, arguably one of the most popular resources on the site, no longer goes to the desired World Factbook homepage directly.

The CIA press release states: “We believe the inconveniences of implementing SSL for the entire website will be offset by increased visitor confidence that they are, in fact, connected to the CIA website and that their visits are secure and confidential.”

The effort to increased security and privacy is commendable, and encrypting all communication with the agency certainly isn't a bad idea. Doing so without the inconveniences would be even better though, and perfectly feasible, too.

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Monday, August 10, 2009


SEO advice: Redirect wisely

More often than not you will see someone recommend switching all redirects on your site to 301s because they pass “link equity” in Google. There is the simple and neat solution for search engine optimization, and it could be plain wrong. At the risk of diverging from the consensus in your favorite discussion forum or offending your SEO consultant, read on and decide for yourself.

Redirects instruct browsers and search engine crawlers that content is available under a different URL. They often go unnoticed as we access Websites. Along with the new location of the content, the server also sends a response code indicating the type of redirect. From an SEO perspective, you generally care about two response codes, 301 Moved permanently and 302 Found:
  • 301 Moved permanently indicates that the resource has been assigned a different URL permanently, and the original URL should no longer be used. What this means for Search engines is that should index the new URL only. Google also transfers full link equity with a 301 redirect, which is the very reason why you will often see the advice to use 301 redirects.
  • 302 Found indicates that the originally requested URL is still valid, and should continue to be used. Search engines vary in how they treat 302 redirects and which URL they show in search result pages, but generally will continue to crawl the original URL as recommended in the HTTP/1.1 specification: “The requested resource resides temporarily under a different URI. Since the redirection might be altered on occasion, the client SHOULD continue to use the Request-URI for future requests.”
Redirects are often used allow the publication of shorter or prettier “vanity” URLs. Shorter URLs are easier to scan and look much more enticing in the search engine results pages, and generally perform better according to MarketingSherpa's 2007 search marketing study and anecdotal evidence.

Choosing the right redirect response code

So which redirect response code should you use? Matt Cutts' description how Google treats on-domain and off-domain 302 redirects covers the basic principles and the heuristics that Google used at the time, which to a large extent still apply.

Let's summarize the effects of the two most common redirect status codes again:
  • 301 redirects transfer link equity to the new URL.
  • 301 redirects remove the original URL from the search index.
  • 302 redirects often keep the original URL in the index.
The transfer of link equity is desirable in almost all cases. So the deciding factor really is whether you prefer the original URL in the index, and if that outweighs the disadvantages of potentially losing some link equity (more on that later).

The 301 redirect response is appropriate for the following scenarios:
  • Content has moved to a different location permanently, for example to a different server name or a different directory structure of the same server. This may be triggered by the rebranding of content where you want all references to the original content to disappear.
  • A Website is accessible under multiple host names, such as example.com and www.example.com, or typo catchers like eggsample.com and example.org, but only one name should be indexed.
  • A temporary campaign URL is published in direct mail or print advertising, but the landing page has a different permanent URL that will remain accessible beyond the lifetime of the campaign.
  • The requested URL does not match the canonical URL for the resource. Often extraneous session and tracking parameters can be stripped, or path information gets added to help with search rankings, for example http://www.amazon.com/Software-Development-Principles-Patterns-Practices/dp/0135974445
The 302 redirect response is the best choice for the following scenarios:
  • The original URL is shorter, prettier, more meaningful, etc. and therefore should show on the search engine results page.
  • Temporary session or tracking information gets added to the canonical URL. Those URL parameters should not be indexed since they will not apply to other visitors.
  • Multiple load balanced servers deliver the content. Indexing an individual server would defeat the purpose of using load balancing. (There are better ways to load balance than having multiple server names, though.)

The “canonical” meta tag

How can you keep the short URL in the index and still transfer link equity? In summer 2008, we started observing that Google somehow “merged” related URLs and treated them as a single entity, showing identical page rank and identical number of inbound links to all of the URLs.

When Google introduced the “canonical” meta tag in February 2009, this suddenly made sense. Once multiple URLs are known to refer to the same page, or a slight variation of a page, the index only needs to keep one instance of the page.

The canonical meta tag helps the webmaster of a site who give search engines a hint about the preferred URL. The canonical meta tag also helps search engines since mapping multiple crawled URLs to the same page and indexing it only once just became easier.

Whether link equity fully transfers between multiple URLs mapped to the same page remains to be seen. At least within the same domain, this unification process may allow keeping the vanity URL in the index with a 302 redirect response while still transferring link equity.

PS. For an excellent and detailed description how redirects work, how to configure your Web server and what each status code does, see Sebstian's pamphlet The anatomy of a server sided redirect: 301, 302 and 307 illuminated SEO wise.

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