How to ensure old links don't become invalid after changing a website's domain? DNS resolution and redirection strategies.

　　Changing a website's domain name is a systematic project with technical complexity far exceeding what is superficially apparent. Many administrators mistakenly believe that simply binding the new domain name to a new server is sufficient, unaware that the invalidation of old links not only means a direct loss of traffic but can also lead to the loss of years of accumulated search engine ranking. In the internet ecosystem, old links are the contractual proof of users' and search engines' trust in your content. Once this proof fails, at best, an embarrassing "404 Not Found" page will appear; at worst, it will trigger a negative evaluation of the website's stability by search engines. To ensure that old links remain "alive" under the new domain name, a rigorous linkage strategy needs to be built from three dimensions: the DNS layer, the server layer, and the application layer.

　　First, understanding the core mechanism of redirection is the foundation for a smooth transition. When a user enters the old domain name in the browser address bar or clicks on an old link that has already been indexed in a search engine, the server needs to return a specific HTTP status code to inform the client that the resource has been permanently moved. The key phrase here is "301 Moved Permanently," which is fundamentally different from a 302 temporary redirect. A 301 redirect is permanent; upon receiving this signal, the search engine explicitly transfers all page weight, ranking signals, and traffic from the old URL to the new URL. Conversely, if a 302 redirect is misused, the search engine will consider it a temporary measure, failing to transfer weight and potentially causing duplicate content issues, leading to competition between the old and new domains in search results, ultimately harming both. Therefore, before implementing any redirect rules, it's crucial to ensure the use of the 301 status code; this is the legal basis for ensuring old links remain valid.

　　In terms of strategy implementation, the ideal situation is to achieve a precise one-to-one mapping between old and new links. A common mistake is to crudely redirect all requests from the old domain to the new website's homepage, for example, redirecting both "old.com/page1.html" and "old.com/page2.html" to "new.com." While simple, this approach is disastrous for user experience and search engine optimization. Users forced to access a specific article and redirected to the homepage will be confused and leave immediately, causing a surge in bounce rate. Search engine crawlers will also consider the old page unrelated to the homepage and unable to transfer specific page weight to the corresponding new page.

　　The correct approach is to maintain consistent URL paths: if the old link is "/product/123", then the target of a 301 redirect should be "new.com/product/123". This requires the old and new websites to maintain the same directory structure, or to use precise redirect rules written with regular expressions. For example, in the .htaccess file of an Apache server, you can use the rule `RewriteRule ^(.*)$ https://newdomain/$1 [R=301,L]`, where the variable `$1` is used to capture all the path after the forward slash of the old domain name and append it unchanged to the new domain name. For an Nginx server environment, the same effect can be achieved using the directive `return 301 https://newdomain$request_uri;`, where the variable `$request_uri` ensures the complete transmission of request parameters and paths.

　　If a 301 redirect solves the "where to go" problem, then DNS resolution solves the "who to look for" problem. Many people mistakenly believe that after changing a domain name, the old domain is no longer needed, and some even delete the old domain's DNS records, which is extremely dangerous. The DNS records for the old domain must be retained, and the A record or CNAME record needs to point to the old server (or, to save resources, to point to the new server, as long as the old server can respond to requests).

　　Why is this necessary? Because a 301 redirect occurs at the server level. When a user accesses the old domain, it first needs to find the IP address of the server hosting the old domain through DNS. After connecting to that server, the server returns a 301 directive telling the browser to access the new domain. If the DNS records are deleted, the user cannot find the server, the connection will time out, and the redirection will be impossible. Furthermore, there is an easily overlooked detail: the TTL (Time to Live) value setting. About a week before planning to change the domain, it is recommended to lower the TTL value in the old domain's DNS records, for example, to 300 seconds (5 minutes). The purpose of this is to ensure that once you configure redirect rules, DNS caches around the world can be quickly refreshed, allowing users to perceive the change as soon as possible, rather than being redirected to the wrong path for the next 24 to 48 hours.

　　However, server-side 301 rules alone are not enough; content-level "hard link" fixing is equally crucial. Hard links refer to absolute addresses stored in the database. For websites built using content management systems (such as WordPress), after a domain change, the old domain's URL is often hardcoded into fields such as article content, featured images, and category links. Even with well-configured server redirects, when users click on images or links within articles, a request to the old domain is still made. Although this may eventually redirect to the new domain via a 301 redirect, it creates an unnecessary redirect, increases page load time, and is not conducive to search engine crawling of deep links.

　　The correct approach is to log into the database and execute SQL replacement statements to batch change the old domains in the stored content to the new domains. For example, for the post table and metadata table, commands like `UPDATE wp_posts SET post_content = REPLACE(post_content, 'old domain', 'new domain');` can be used to completely remove traces of the old domain from internal links. If you're uneasy about directly manipulating the database, you can use visual plugins like "Better Search Replace," which effectively avoid data loss due to SQL syntax errors and handle serialized data issues.

　　After all the technical steps are completed, the final step is to communicate with the search engine. Even if you perfectly configure 301 redirects, search engine crawlers need time and clear instructions to understand this significant architectural change. Currently, mainstream search engines (such as Baidu, Google, and Bing) provide "website redesign" or "address change" functions in their webmaster tools. You need to verify ownership on both the old and new domain sites, then submit the redesign rules, clearly informing the search engine that all directories under the old domain have permanently pointed to the corresponding directories under the new domain. This action is equivalent to giving the search engine a "map," which can greatly shorten the indexing cycle of the new domain and accelerate the migration of authority. Statistics show that by proactively submitting a redesign tool and using correct 301 sitewide redirects, the indexing speed of a new domain can increase several times. Without this submission, a complete transfer of authority could take several months. Furthermore, the renewal and management of the old domain should not be neglected. It is recommended to retain the old domain for at least one year and maintain 301 redirects throughout this period to prevent it from being registered by others after expiration, which could redirect traffic intended for your website to malicious sites.

　　【Frequently Asked Questions】

　　Q: Can I shut down the old server after changing my website's domain name?

　　A: Absolutely not. As long as the old domain is still resolving DNS and providing 301 redirect services, you need a server capable of responding to requests. If you are no longer renting the old server, you can point the old domain's DNS resolution to the new server's IP address and set up a separate virtual host configuration for the old domain in the new server's site configuration. This virtual host should only contain 301 redirect rules and not store any actual files. This saves resources while maintaining the redirect functionality.

　　Q: What if the URL structures of the old and new websites don't correspond one-to-one?

　　A: In reality, website redesigns can completely change the paths to category pages. Wildcard rules won't work in this case; you'll need to create a "redirect mapping table." List the new URLs corresponding to the old URLs in the server's configuration file. For example, `Redirect 301 /old-about.php https://new.com/about-us/`. Although manual maintenance is tedious, for user experience and SEO, mapping each URL individually is far better than redirecting all URLs to the homepage. For dead links where the corresponding page cannot be found, it's better to return a 404 status code than to redirect to the homepage, as the latter will be considered a soft 404 by search engines, negatively impacting the website's reputation.

　　Q: Is explicit URL forwarding in domain name resolution considered a 301 redirect?

　　A: Most domain registrars' "explicit URL forwarding" functionality is often implemented as a temporary 302 redirect or through a frame page, and is extremely unstable and unfriendly to search engines. The truly professional approach is to resolve the domain name to the server IP address and then manually configure 301 rules in the server software (Apache/Nginx). The forwarding function in the domain control panel is only suitable for non-website purposes or temporary testing scenarios and should never be the primary solution for website migration.

　　Q: Is it normal for rankings to drop in the short term after changing the domain name?

　　A: This is normal. Even with perfect execution, search engines need time to re-evaluate the new domain. There is usually a "shock period" of 2 to 4 weeks or even longer, during which keyword rankings may fluctuate or temporarily disappear. As long as the 301 redirect configuration is correct, the new site's content quality is consistent with the old site, and the redesign has been submitted through webmaster tools, the ranking will usually gradually recover and stabilize within 1 to 3 months. If the ranking still shows no improvement after 3 months, it is necessary to check for issues such as a broken redirect chain, a penalty for the new domain, or a decline in website content quality.