diff --git a/lib/logstash/filters/cidr.rb b/lib/logstash/filters/cidr.rb
new file mode 100644
index 000000000..afa979901
--- /dev/null
+++ b/lib/logstash/filters/cidr.rb
@@ -0,0 +1,75 @@
+require "logstash/filters/base"
+require "logstash/namespace"
+require "ipaddr"
+
+# The CIDR filter is for checking IP addresses in events against a list of
+# network blocks that might contain it. Multiple addresses can be checked
+# against multiple networks, any match succeeds. Upon success additional tags
+# and/or fields can be added to the event.
+
+class LogStash::Filters::CIDR < LogStash::Filters::Base
+
+  config_name "cidr"
+  plugin_status "experimental"
+
+  # The IP address(es) to check with. Example:
+  #
+  #     filter {
+  #       %PLUGIN% {
+  #         add_tag => [ "testnet" ]
+  #         address => [ "%{src_ip}", "%{dst_ip}" ]
+  #         network => [ "192.0.2.0/24" ]
+  #       }
+  #     }
+  config :address, :validate => :array, :default => []
+
+  # The IP network(s) to check against. Example:
+  #
+  #     filter {
+  #       %PLUGIN% {
+  #         add_tag => [ "linklocal" ]
+  #         address => [ "%{clientip}" ]
+  #         network => [ "169.254.0.0/16", "fe80::/64" ]
+  #       }
+  #     }
+  config :network, :validate => :array, :default => []
+
+  public
+  def register
+    # Nothing
+  end # def register
+
+  public
+  def filter(event)
+    return unless filter?(event)
+
+    address = @address.collect do |a|
+      begin
+        IPAddr.new(event.sprintf(a))
+      rescue ArgumentError => e
+        @logger.warn("Invalid IP address, skipping", :address => a, :event => event)
+        nil
+      end
+    end
+    address.compact!
+
+    network = @network.collect do |n|
+      begin
+        IPAddr.new(event.sprintf(n))
+      rescue ArgumentError => e
+        @logger.warn("Invalid IP network, skipping", :network => n, :event => event)
+        nil
+      end
+    end
+    network.compact!
+
+    # Try every combination of address and network, first match wins
+    address.product(network).each do |a, n|
+      @logger.debug("Checking IP inclusion", :address => a, :network => n)
+      if n.include?(a)
+        filter_matched(event)
+        return
+      end
+    end
+  end # def filter
+end # class LogStash::Filters::CIDR