Help Center/ Web Application Firewall/ User Guide (Paris) / Cloud WAF/ Getting Started/ Allowing WAF Back-to-Source IP Addresses to Access Origin Servers
Updated on 2023-05-16 GMT+08:00
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Allowing WAF Back-to-Source IP Addresses to Access Origin Servers

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. Otherwise, your website visitors will frequently receive 502 or 504 error code when your website is connected to WAF in cloud mode.

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 service scale-out or new clusters. For your legacy domain names, WAF 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 DR 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

WAF Back-to-Source IP Address Check Mechanism

A back-to-source IP address, or WAF IP address, is randomly allocated from the back-to-source IP address range. When WAF forwards requests to the origin server, WAF will check the IP address status. If the IP address is abnormal, WAF will remove it and randomly allocate a normal one to receive or send requests.

WAF back-to-source IP addresses are periodically updated. Whitelist the new IP addresses in time to prevent these IP addresses from being blocked by origin servers.

Why Do I Need to Whitelist the WAF 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 IP addresses are blocked, the website may fail to be accessed or it opens extremely slowly. To fix this, add the WAF 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.

Procedure

  1. Log in to the management console.
  2. Click in the upper left corner of the management console and select a region or project.
  3. Click Service List at the top of the page and choose Security > Web Application Firewall.
  4. In the navigation pane on the left, choose Domains to go to the domain name settings page.
  5. Above the website list, click WAF Back-to-Source IP Addresses.
  6. In the displayed dialog box, click Copy to copy all the addresses.
  7. Open the security software on the origin server and add the copied IP addresses to the whitelist.
Parent topic: Getting Started