pip: OpenStack avoids newer eventlet
-eventlet>=0.15
+# NOTE: OpenStack avoids the newer versions of eventlet, because of the
+# following issue.
+# https://github.com/eventlet/eventlet/issues/401
+eventlet!=0.18.3,>=0.18.2,<0.21.0
msgpack-python>=0.3.0 # RPC library, BGP speaker(net_cntl)
netaddr
oslo.config>=1.15.0
