What are the types of domain name redirection and resolution? A summary of important considerations.

　　Have you ever encountered this situation when visiting a website: you type in a URL, and before you even realize it, the content in the address bar automatically changes. Sometimes the "www" prefix suddenly appears, sometimes "http" becomes "https," and sometimes even the entire domain name changes. This phenomenon of "automatic address switching" is technically called domain redirection, also known as URL redirection.

　　Many people think this is simple—just setting up a forwarding function, done in minutes. But in reality, domain redirection is far more complex than you imagine. An incorrect redirection setting can, at best, cause problems with your website's indexing, and at worst, lead to a complete loss of users, or even wipe out your SEO efforts overnight. Today, I'll explain domain redirection in detail, not as a dry technical manual, but as a practical guide from someone who has encountered and corrected these pitfalls.

　　I. First, understand: What exactly does domain redirection do?

　　Before discussing the types, we need to understand a core question: What is the essence of domain redirection?

　　Simply put, when a user enters an address A in their browser, the server or DNS system tells them, "Don't go to A, go to B," and the browser automatically redirects the user to B. This process is domain redirection.

　　Sounds simple, right? But there's a crucial dividing line: at what stage does this "telling them" action occur?

　　Some redirects occur at the DNS level—that is, after you enter the address but before connecting to the server, the DNS server directly returns a new address, telling the browser, "You've got the wrong address, this is the correct one." This is called a DNS-level redirect, also known as an explicit or implicit redirect (more on this later).

　　Some redirects occur at the server level—the browser has already connected to the server, and the server, while processing the request, returns a special instruction telling the browser, "What you're looking for isn't here, look there." This is called an HTTP-level redirect.

　　While these two types of redirects may seem similar in their final effect, their underlying logic, applicable scenarios, and impact on SEO are vastly different.

　　II. Type One: DNS-Level Redirection – The Easiest, But Also the Most Dangerous

　　DNS-level redirection is a "foolproof" feature provided by many domain registrars. You simply click a few buttons in the backend to set old.com to redirect to new.com, and then you don't need to do anything else.

　　This type of redirection is further divided into two types: explicit redirection and implicit redirection.

　　1. Explicit Redirection (Also called 301 Redirect)

　　Explicit redirection means that when a user enters A, the address bar directly changes to B, clearly informing the user that "you've arrived at the new location."

　　This type of redirection is achieved by the domain registrar returning a "status code 301" instruction at the DNS level. Upon receiving this instruction, the browser automatically redirects to the new address and records this redirection.

　　2. Implicit Redirect (Also called Hidden Redirect, Frame Redirect)

　　This is where many people easily fall into the trap.

　　The effect of an implicit redirect is: when a user enters A, the address bar still displays A, but the page content is actually loaded from B. It's implemented by loading the target website within a hidden iframe.

　　Sounds great, right? You protect your own domain and use the target website's content.

　　But here's the problem: search engines see an empty shell page with a frame embedded inside. They can hardly access the actual content of the target website, and therefore cannot give this domain any ranking. Even worse, if your target website itself has SEO authority, an implicit redirect won't transfer any authority to your A domain.

　　Furthermore, this type of redirect provides a terrible user experience on mobile devices—iframe scrolling, adaptation, and loading speed are all problems. Many mobile browsers will even issue warnings for such framed pages.

　　My advice is: unless you have very specific needs, never use implicit redirects. The slight benefit of a "unchanged address bar" is far from enough to offset the losses it causes in SEO and user experience.

　　III. Type Two: HTTP-Level Redirects – Flexible, But Require Manual Control

　　HTTP-level redirects require control over the server, configured at the Nginx, Apache, or code level. While the barrier to entry is higher, the controllability far exceeds that of DNS-level redirects.

　　The three most common status codes at this level are: 301, 302, and 307.

　　1. 301 Permanent Redirect

　　This is the most respected redirect method in the SEO field.

　　A 301 means "This page has been permanently moved to a new address." When a search engine receives a 301, it will do several things: transfer all the weight (PageRank, traffic value) of the old page to the new page; replace the old address with the new address in search results; and never crawl the old address again unless there are special circumstances.

　　When to use a 301 redirect?

　　Domain change: From oldsite.com to newsite.com

　　HTTP to HTTPS upgrade: Redirect from http:// to https://

　　URL structure change: Change from /?id=123 to /product-name

　　Unifying WWW and non-WWW URLs: Permanently redirect one to the other

　　2. 302 Temporary Redirect

　　A 302 redirect means "This page has been temporarily moved elsewhere and will be back later."

　　When a search engine receives a 302 redirect, it will continue to index the old page and will not transfer its ranking weight to the new page. This is because the search engine considers it temporary and expects the old page to be restored after a period of time.

　　When to use a 302 redirect?

　　A/B testing: Temporarily redirect some traffic to the new version of the page.

　　Promotional activities: Restore the original page after the promotion ends.

　　Website maintenance: Temporarily redirect traffic to the maintenance notification page.

　　A common pitfall is that some people mistakenly use 302 instead of 301, resulting in the new domain not ranking well after a domain migration, while the old domain remains in search results. This is because the search engine hasn't transferred the ranking weight.

　　3. 307 Temporary Redirect (Special Scenario for HTTP to HTTPS)

　　307 is essentially the same as 302, a temporary redirect. However, there is an important difference: 307 guarantees that the request method (GET, POST) will not change during the redirect.

　　This feature is particularly useful when upgrading from HTTP to HTTPS. If you use 302, in some cases a POST request might be changed to a GET, leading to data loss. 307, on the other hand, preserves the original request method.

　　However, in practice, most websites still use 301 redirects when upgrading to HTTPS because it's a permanent change.

　　IV. Easily Overlooked Redirect Type: Meta Refresh

　　There's another type of redirection, neither at the DNS nor HTTP level, but within the page itself—Meta Refresh.

　　It involves adding a line of code to the `<head>` tag in the HTML:

<meta http-equiv="refresh" content="0; url=https：//xxxx.com/">

　　This redirection method has a poor user experience: the old page loads first, then the user is redirected to the new page. Even if you set `content` to 0, this process still produces a "flicker," and the user sees the old page flash by.

　　From an SEO perspective, search engines handle Meta Refresh inconsistently. While Google can recognize it, its weight transfer effect is far less than 301. Baidu's handling of it is even more unstable.

　　Unless you have absolutely no control over the server, it's not recommended to use Meta Refresh. It's like a "last resort"—avoid it if possible.

　　V. Five Common Pitfalls in Domain Redirection

　　Now that the theory is covered, let's talk about practical issues—the pitfalls I've encountered in redirect settings over the years, and how to avoid them.

　　Pitfall 1: Overly Long Redirect Chains

　　What is a redirect chain? It's when A jumps to B, B jumps to C, and C then jumps to D.

　　For example, you might set up http://old.com → https://old.com → https://www.old.com → https://www.new.com.

　　Each redirect means an additional HTTP request, significantly increasing page load time. Furthermore, search engines reduce the efficiency of weight transfer with each redirect.

　　Correct Practice: Jump directly from the old address to the final address, without any intermediate "redirecting stations." All redirect rules should point to the final destination, not to another redirect rule.

　　Pitfall 2: Mixing 301 and 302 Redirects

　　Some people migrate their domains, using a 302 redirect from the old to the new domain, thinking, "It's bypassed anyway." However, months later, the new domain still has no ranking, while the old domain remains in search results.

　　Correct Practice: For permanent changes such as domain migration, HTTPS upgrades, and consistent www redirects, a 301 redirect is mandatory. 302 redirects should only be used for temporary scenarios.

　　Pitfall 3: Incomplete HTTPS Redirects

　　Many people only implement "HTTP redirect to HTTPS," forgetting to implement "HTTPS non-www redirect to HTTPS with www" (or vice versa). The result is that your website has four versions existing concurrently in the search engine's eyes:

• http://example.com
• http://www.example.com
• https://example.com
• https://www.example.com

　　These four versions are seen as four different websites by the search engine, resulting in diluted ranking and a large amount of duplicate content.

　　Correct Practice: Keep only one valid URL, and redirect the other three URLs to this valid URL using a 301 redirect.

　　Pitfall 4: Overly Broad Redirect Rules

　　For example, you might want to redirect old.com/a.html to new.com/a.html, but mistakenly write "Redirect all pages under old.com to the new.com homepage."

　　The problem is that users who want to see page A are redirected to the homepage, leaving them confused. Search engines will also consider this redirect "irrelevant," affecting the transfer of page ranking.

　　Correct Practice: Maintain a consistent URL structure to achieve precise "one-to-one" redirects. If this isn't possible, at least ensure the redirected page is highly relevant to the original page's theme.

　　Pitfall 5: Failure to Update Sitemap and Internal Links After Redirection

　　Many people think they're done after setting up redirect rules. However, if your website's internal links still point to the old address, clicking these links will still trigger a redirect, increasing loading time.

　　Correct practice: After setting up the redirect rules, update all URLs in the sitemap (sitemap.xml) as soon as possible, and change all internal links on the website to the new addresses. Although this step is tedious, it has real benefits for user experience and SEO.

　　VI. Suggestions for Handling Several Special Scenarios

　　Scenario 1: Domain Change

　　This is the scenario that most tests your redirection skills. Besides setting up 301 redirects, there are a few other things you must do:

• Submit a "Change Domain" or "Address Change" application in Google Search Console and Baidu Webmaster Tools.
• Ensure the content of the old and new domains corresponds one-to-one, avoiding widespread 404 errors.
• Keep the old and new domains running concurrently for at least 6 months, until the search engine fully recognizes the new domain.

　　Scenario Two: HTTPS Upgrade

　　While this scenario is already standard, details can easily lead to problems:

• The certificate must cover all domains that need to be redirected (including those with and without www).
• Enable HSTS (HTTP Strict Transport Security) to tell browsers to always use HTTPS, reducing the number of redirects.
• Check mixed content carefully, ensuring that images, scripts, and stylesheets referenced on the page are also HTTPS.

　　Scenario Three: Mobile and PC Separation

　　If your website has a mobile-only site, you need to redirect users on the server side based on their device. However, there's a crucial point: never use JavaScript for redirects, as search engine crawlers may not execute JavaScript.

　　The correct approach is to return a 302 temporary redirect on the server side (Nginx, Apache) by checking the User-Agent, and simultaneously add a Vary: User-Agent response header to tell the search engine that this is a redirect based on the device type.

　　Scenario 4: Redirects in a CDN Environment

　　If you're using a CDN, the location of your redirect rules becomes very important. Some CDNs handle redirects directly at edge nodes, bypassing your origin server. In this case, you need to ensure that the CDN's redirect rules and the origin server's redirect rules do not conflict; otherwise, a "redirect loop" may occur.

　　VII. After Redirecting, Don't Forget to Check and Monitor

　　The final step, and the most easily overlooked, is to verify that the redirect is correct.

　　You can use online tools to test this. Enter the old address and see if the returned status code is the expected 301 and if the final landing address is correct. More importantly, monitor the data changes after the redirect takes effect: Is the traffic to the old address gradually decreasing? Is the traffic to the new address steadily increasing? Are there any widespread 404 errors?

　　If, within a month of the redirect taking effect, the traffic to the new address does not recover to more than 80% of the old address, then your redirect settings likely have a problem and need to be checked again.

　　Domain redirection may seem like a small part of website operations, but its impact is very broad—user experience, SEO ranking, brand consistency, and even security are all closely related to it. A good redirect strategy should be: seamless for users and search engine friendly.