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Philippe_Page_2's avatar
Philippe_Page_2
Icon for Cirrus rankCirrus
Jan 22, 2019

Error 521: Web server is down - Cloudflare generated error

I have an virtual server created with many websites hosted in it. It has one public IP assigned to it and is NATed to a private IP. The websites are accessible via HTTP and HTTPS. However one website uses Cloudflare, there are times that when we are browsing that website we sometimes come across with error 521. Sometimes after refreshing the web page, the error will no longer present itself sometimes the error is still present even after refreshing several times. I have whitelisted the cloudflare IP addresses onto F5 via Network ›› Packet Filters : Rules

 

I am running software version 12.1.3

 

application delivery
BIG-IP
cloudflare
LTM
security

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  • JG's avatar
    JG
    Icon for Cumulonimbus rankCumulonimbus
    Jan 23, 2019

    "521" is a Cloudflare-specific error code, issued when its reverse proxy server's connection to the origin content server was refused. You might want to investigate the issue on the origin content server itself.