Help Center/ Web Application Firewall/ Help Panel/ Tier-2 Help Panel - Website Settings/ Step 2: Whitelist WAF Back-to-Source IP Addresses (Cloud Mode)
Updated on 2025-04-25 GMT+08:00
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Step 2: Whitelist WAF Back-to-Source IP Addresses (Cloud Mode)

To let your cloud WAF instances take effect, configure ACL rules on the origin server to trust only the back-to-source IP addresses of all your cloud WAF instances. This prevents hackers from attacking the origin server through the server IP addresses.

ACL rules must be configured on the origin server to whitelist WAF back-to-source IP addresses, or your website visitors will frequently receive 502 or 504 error code.

What Are Back-to-Source IP Addresses?

From the perspective of a server, all web requests originate from WAF. The IP addresses used by WAF forwarding are back-to-source IP addresses of WAF. The real client IP address is written into the X-Forwarded-For (XFF) HTTP header field.

  • There will be more WAF back-to-source IP addresses due to scale-out or new clusters. For your legacy domain names, WAF back-to-source IP addresses usually fall into several class C IP addresses (192.0.0.0 to 223.255.255.255) of two to four clusters.
  • Generally, these IP addresses do not change unless clusters in use are changed due to disaster recovery switchovers or other scheduling switchovers. Even when WAF cluster is switched over on the WAF background, WAF will check the security group configuration on the origin server to prevent service interruptions.
Figure 1 Back-to-source IP address

Why Do I Need to Whitelist the WAF Back-to-Source IP Address Ranges?

All web requests originate from a limited quantity of WAF IP addresses. The security software on the origin server may most likely regard these IP addresses as malicious and block them. Once WAF back-to-source IP addresses are blocked, the website may fail to be accessed or it opens extremely slowly. To fix this, add the WAF back-to-source IP addresses to the whitelist of the security software.

After you connect your website to WAF, uninstall other security software from the origin server or allow only the requests from WAF to access your origin server. This ensures normal access and protects the origin server from hacking.

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Parent Topic: Tier-2 Help Panel - Website Settings