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Forum Discussion

rmoss25's avatar
rmoss25
Icon for Altostratus rankAltostratus
Mar 11, 2021

Preserve Original Source IP thats not just Web Traffic

Hi, Is there a way to preserve the original source IP of traffic passing through an LTM Virtual server? We have enabled the Insert X-Forwarded-For option in the HTTP profile and while this works fo...
BIG-IP
devops
LTM
security
eey0re's avatar
eey0re
Icon for Cirrostratus rankCirrostratus
Mar 16, 2021

Obviously other protocols don't have "X-Forwarded-For", so the only way to preserve the source IP is to actually preserve the source IP: turn off SNAT in the Virtual Server so that the source address is not translated.

 

This is a "routed" configuration, rather than a "SNAT" configuration, and means the backend server will see the connection as from the real client IP.

 

  • All the return traffic still needs to pass back through the BIG-IP, so the backend server must now use the BIG-IP's floating Self IP as its gateway. (For Internet traffic, this generally means the BIG-IP becomes the server's default route.)

 

  • The backend server therefore needs to be on the same subnet as a BIG-IP Self IP to be able to use it as a gateway.

 

  • The server still needs to be able to reach everything else that didn't come via the Virtual Server. Usually this means:
    • some more specific routes on the server to keep using its regular router, and/or
    • a wildcard Virtual Server on the BIG-IP of type "Forwarding (IP)" combined with appropriate routes on the BIG-IP so it knows where to forward to.

 

As you can see this is quite a different design. For more information see About Virtual Servers in the BIG-IP Local Traffic Management: Basics manual.