Please always follow these steps:

[x] Confirmed this is a problem with brew installing one, specific formula (not cask) and not every time you run brew? If it's a general brew problem please file this issue at https://github.com/Homebrew/brew/issues/new. If it's a brew cask problem please file this issue at https://github.com/Homebrew/caskroom/homebrew-cask/new
[x] Ran brew update and retried your prior step?
[x] Ran brew doctor, fixed all issues and retried your prior step?
[x] Ran brew gist-logs <formula> (where <formula> is the name of the formula that failed) and included the output link?
[x] If brew gist-logs didn't work: ran brew config and brew doctor and included their output with your issue?

The geoip formula installs without the required data files for geoiplookup to work correctly. The data files will not be downloaded by the accompanying geoipupdate program without some modifification to the /usr/local/Cellar/geoipupdate/{VERSION}/etc/GeoIP.conf file, as documented here. The conf file needs these two lines before geoipupdate will work correctly:

UserId 999999
ProductIds GeoLite2-City GeoLite2-Country GeoLite-Legacy-IPv6-City GeoLite-Legacy-IPv6-Country 506 517 533

brew config && brew doctor:

[q@x/0 ~] brew config
HOMEBREW_VERSION: 1.2.4-27-gf1fa475c4
ORIGIN: https://github.com/Homebrew/brew.git
HEAD: f1fa475c4fc6f82312368114bdd604d5752e743b
Last commit: 4 days ago
Core tap ORIGIN: https://github.com/Homebrew/homebrew-core
Core tap HEAD: e1f1ba00224ec173fa0334b1613182ed5ec2d6f0
Core tap last commit: 3 days ago
HOMEBREW_PREFIX: /usr/local
HOMEBREW_REPOSITORY: /usr/local/Homebrew
HOMEBREW_CELLAR: /usr/local/Cellar
HOMEBREW_BOTTLE_DOMAIN: https://homebrew.bintray.com
CPU: quad-core 64-bit broadwell
Homebrew Ruby: 2.0.0-p648
Clang: 8.1 build 802
Git: 2.13.2 => /usr/local/bin/git
Perl: /usr/local/bin/perl => /usr/local/Cellar/perl/5.26.0/bin/perl
Python: /usr/local/bin/python => /usr/local/Cellar/python/2.7.13/Frameworks/Python.framework/Versions/2.7/bin/python2.7
Ruby: /usr/local/bin/ruby => /usr/local/Cellar/ruby/2.4.1_1/bin/ruby
Java: N/A
macOS: 10.12.5-x86_64
Xcode: N/A
CLT: 8.3.2.0.1.1492020469
X11: N/A
[q@x/0 ~] brew doctor
Please note that these warnings are just used to help the Homebrew maintainers
with debugging if you file an issue. If everything you use Homebrew for is
working fine: please don't worry and just ignore them. Thanks!

Warning: You have a curlrc file
If you have trouble downloading packages with Homebrew, then maybe this
is the problem? If the following command doesn't work, then try removing
your curlrc:
  curl https://github.com

Homebrew / homebrew-core

geoip package doesn't work without config changes #15539

Please always follow these steps: