Configuring Custom Domains in Multisite

Configuring Custom Domains in WordPress Multisite

WordPress Multisite is a powerful feature that allows you to run multiple sites from a single WordPress installation. While subdomains or subdirectories are the default configurations, mapping custom domains to individual sites within the network provides a professional, brand-aligned experience. This article provides a comprehensive guide—covering prerequisites, step-by-step instructions, SSL considerations, troubleshooting, and best practices—to help you implement and manage custom domains on your Multisite network.

1. Understanding Domain Mapping

Domain mapping connects a custom domain (e.g., www.example.com) to a specific subsite in your network (e.g., site1.network.com). There are two primary approaches:

• Plugin-Based Mapping: Uses third-party plugins to handle URL rewriting and admin settings.
• Domain Mapping in Core: Since WordPress 4.5, domain mapping capabilities are built into core Multisite, reducing plugin reliance.

2. Prerequisites

• A WordPress Multisite installation (subdomain or subdirectory mode enabled).
  Official Guide: Creating a Network
• Access to your DNS management console (domain registrar or hosting control panel).
• Server configuration allowing wildcard domains or individual virtual hosts (Apache/nginx).
  WP Developer Handbook: Domain Mapping
• SSL certificate for each custom domain or a wildcard certificate.

3. DNS Configuration

Proper DNS records ensure your custom domain points to your Multisite server IP. Use either a wildcard record or individual A/CNAME records:

Record Type	Host/Name	Value	Use Case
A	@ or site1	123.45.67.89	Direct mapping for apex or subdomain
CNAME	www	network.com	Alias pointing to primary domain
A (wildcard)		123.45.67.89	Catches all subdomains

4. Enabling Domain Mapping in Core

1. Enable Multisite: Add define(WP_ALLOW_MULTISITE, true) to wp-config.php.
2. Follow the network setup instructions (subdomain/subdirectory mode).
3. Ensure SUNRISE is set only if using legacy plugins otherwise skip:
   • define(SUNRISE, on) in wp-config.php.
4. Network Admin → Sites → Edit a site → Site Address (URL): enter your custom domain (e.g., https://www.example.com).

5. Plugin-Based Mapping (Optional)

If you prefer a GUI and advanced features (redirect management, SSL automation), consider a plugin:

• WordPress MU Domain Mapping: Lightweight, widely used. Plugin Page.
• Mercator: Modern alternative supporting IPv6, WP-CLI. GitHub Repository.

General installation steps:

1. Upload plugin to wp-content/plugins and network‐activate.
2. Configure settings under Network Admin → Settings → Domain Mapping.
3. Add each domain to its corresponding subsite via Sites → Edit → Domains.

6. SSL Certificate Management

Secure custom domains with TLS/SSL. Choose one of the following:

• Wildcard Certificate: Covers .network.com but not external domains.
• Individual Certificates: One certificate per mapped domain. Use Let’s Encrypt for free automation.
• SAN Certificate: Single certificate listing multiple domains in SAN fields.

Implement via your web server:

• Apache: ltVirtualHost :443gt ServerName www.example.com SSLCertificateFile …lt/VirtualHostgt
• nginx: server { listen 443 server_name www.example.com ssl_certificate … }

7. Advanced Considerations

7.1 Session Cookies Cross-Domain

To maintain admin sessions across domains, add in wp-config.php:

define(COOKIE_DOMAIN, false)
define(ADMIN_COOKIE_PATH, /)
define(COOKIEPATH, )
define(SITECOOKIEPATH, )

7.2 Email Delivery

Custom domains must align with your mail service to avoid SPF/DKIM/DMARC issues. Update DNS with:

• SPF record: v=spf1 include:yourmailprovider.com -all
• DKIM and DMARC as per provider instructions.

8. Troubleshooting Common Issues

• 404 Not Found: Verify DNS propagation and web-server virtual host mapping.
• Mixed Content: Ensure https:// is forced network-wide (Network Admin → Settings → HTTPS).
• Login Redirect Loop: Clear browser cookies confirm COOKIE_DOMAIN settings.
• Admin Bar Missing: Check if DOCUMENT_ROOT is correctly set in server config.

9. Best Practices

1. Plan domain naming conventions centrally to avoid conflicts.
2. Use automated SSL tools (Certbot, acme.sh) for renewals.
3. Document each site’s DNS settings and SSL expiration dates.
4. Regularly update WordPress core, themes, and plugins for security.
5. Monitor DNS propagation and certificate health via uptime services.

10. References

• WordPress.org: Create a Network
• WordPress Developer Handbook: Domain Mapping
• WordPress MU Domain Mapping Plugin
• Let’s Encrypt Official Site