Add ability to blacklist ip ranges for federation traffic (#5043)

docs/sample_config.yaml

@@ -115,6 +115,24 @@ pid_file: DATADIR/homeserver.pid
 #  - nyc.example.com
 #  - syd.example.com
 
+# Prevent federation requests from being sent to the following
+# blacklist IP address CIDR ranges. If this option is not specified, or
+# specified with an empty list, no ip range blacklist will be enforced.
+#
+# (0.0.0.0 and :: are always blacklisted, whether or not they are explicitly
+# listed here, since they correspond to unroutable addresses.)
+#
+federation_ip_range_blacklist:
+  - '127.0.0.0/8'
+  - '10.0.0.0/8'
+  - '172.16.0.0/12'
+  - '192.168.0.0/16'
+  - '100.64.0.0/10'
+  - '169.254.0.0/16'
+  - '::1/128'
+  - 'fe80::/64'
+  - 'fc00::/7'
+
 # List of ports that Synapse should listen on, their purpose and their
 # configuration.
 #