Load Balancer Internal IP’s Appearing in IIS/Apache Logs: Quick Fix

If you are NAT’ing public to private addresses with a load balancer in between your web server and your Gateway/FireWall device you might come across the situation where the IIS/Apache logs report the IP of the Load Balancer, when what you really want, is the client IP.

It’s obvious that the biggest issue with this is that any Log Parser/Analytic’s you do against the site will all be relative to the IP of the load balancer. All useful client and geographical information is lost.

Most Load Balancer’s get around this by inserting a Header into the packet that relates to Client IP. In most cases that I have seen, both Juniper and NetScalers the Header is set to rlnclientipaddr.

What needs to be done at the web server configuration level to help pick up on and translate the header info so it can be used to translate the correct client IP into the log files. There are obviously different way to achieve this in Apache, compared to IIS and Apache has a much simply solution than IIS.

Apache:

In your apache.conf go to the LogFormat sections and modify the default format as shown below (Replace the Red text with the green text) and restart the Apache Service.


IIS
:

The IIS 5/6/7/8 solution is a little more involved, but still just as efficient and not overly complicated at the end of the day…in fact for me the hardest part was actually chasing up the DLL’s linked below. It must be noted that while this has worked perfectly for me against both a Juniper DX and NetScaler VPX load balancer I would suggest testing the solution before putting it into production. Reason being is that the ISAPI filters are specifically sourced for the Juniper DX series, but in my testing I found that they worked for the NetScalers as well. Sourcing the x64 DLL’s was a mission, so in this I am saving you a great deal of time by provided the files below.

rllog-ISAPI

Download and extract those files into your Windows root. Go to the Features View -> ISAPI Filters and Click on Add. Enter in the Name and Executable Location and click ok. Note that it’s handy to add both 32 and 64 bit version to a 64bit IIS Web Server just in case you are dealing with legacy Application that are required to run in 32bit mode. Adding the ISAPI Filter at the root config of the Web Server so it propagates down to all existing sites and any newly created sites.

isapi_dll