diff --git a/PKG-INFO b/PKG-INFO
index fd57a49..0a66b71 100644
--- a/PKG-INFO
+++ b/PKG-INFO
@@ -1,6 +1,6 @@
 Metadata-Version: 2.1
 Name: certbot-dns-rfc2136
-Version: 1.18.0
+Version: 1.21.0
 Summary: RFC 2136 DNS Authenticator plugin for Certbot
 Home-page: https://github.com/certbot/certbot
 Author: Certbot Project
diff --git a/certbot_dns_rfc2136/__init__.py b/certbot_dns_rfc2136/__init__.py
index 3c57483..077a731 100644
--- a/certbot_dns_rfc2136/__init__.py
+++ b/certbot_dns_rfc2136/__init__.py
@@ -33,7 +33,7 @@
    :name: credentials.ini
    :caption: Example credentials file:
 
-   # Target DNS server
+   # Target DNS server (IPv4 or IPv6 address, not a hostname)
    dns_rfc2136_server = 192.0.2.1
    # Target DNS port
    dns_rfc2136_port = 53
diff --git a/certbot_dns_rfc2136/_internal/dns_rfc2136.py b/certbot_dns_rfc2136/_internal/dns_rfc2136.py
index 77007a9..98687e6 100644
--- a/certbot_dns_rfc2136/_internal/dns_rfc2136.py
+++ b/certbot_dns_rfc2136/_internal/dns_rfc2136.py
@@ -15,6 +15,7 @@
 from certbot import errors
 from certbot.plugins import dns_common
 from certbot.plugins.dns_common import CredentialsConfiguration
+from certbot.util import is_ipaddress
 
 logger = logging.getLogger(__name__)
 
@@ -54,7 +55,11 @@
         return 'This plugin configures a DNS TXT record to respond to a dns-01 challenge using ' + \
                'RFC 2136 Dynamic Updates.'
 
-    def _validate_algorithm(self, credentials):
+    def _validate_credentials(self, credentials):
+        server = credentials.conf('server')
+        if not is_ipaddress(server):
+            raise errors.PluginError("The configured target DNS server ({0}) is not a valid IPv4 "
+                                     "or IPv6 address. A hostname is not allowed.".format(server))
         algorithm = credentials.conf('algorithm')
         if algorithm:
             if not self.ALGORITHMS.get(algorithm.upper()):
@@ -69,7 +74,7 @@
                 'secret': 'TSIG key secret',
                 'server': 'The target DNS server'
             },
-            self._validate_algorithm
+            self._validate_credentials
         )
 
     def _perform(self, _domain, validation_name, validation):
diff --git a/certbot_dns_rfc2136.egg-info/PKG-INFO b/certbot_dns_rfc2136.egg-info/PKG-INFO
index fd57a49..0a66b71 100644
--- a/certbot_dns_rfc2136.egg-info/PKG-INFO
+++ b/certbot_dns_rfc2136.egg-info/PKG-INFO
@@ -1,6 +1,6 @@
 Metadata-Version: 2.1
 Name: certbot-dns-rfc2136
-Version: 1.18.0
+Version: 1.21.0
 Summary: RFC 2136 DNS Authenticator plugin for Certbot
 Home-page: https://github.com/certbot/certbot
 Author: Certbot Project
diff --git a/certbot_dns_rfc2136.egg-info/requires.txt b/certbot_dns_rfc2136.egg-info/requires.txt
index 6bdfd92..94ab74a 100644
--- a/certbot_dns_rfc2136.egg-info/requires.txt
+++ b/certbot_dns_rfc2136.egg-info/requires.txt
@@ -1,8 +1,7 @@
-dnspython
+dnspython>=1.15.0
 setuptools>=39.0.1
-zope.interface
-acme>=1.18.0
-certbot>=1.18.0
+acme>=1.21.0
+certbot>=1.21.0
 
 [docs]
 Sphinx>=1.0
diff --git a/setup.py b/setup.py
index b7f84bc..7e105e4 100644
--- a/setup.py
+++ b/setup.py
@@ -4,12 +4,11 @@
 from setuptools import find_packages
 from setuptools import setup
 
-version = '1.18.0'
+version = '1.21.0'
 
 install_requires = [
-    'dnspython',
+    'dnspython>=1.15.0',
     'setuptools>=39.0.1',
-    'zope.interface',
 ]
 
 if not os.environ.get('SNAP_BUILD'):
diff --git a/tests/dns_rfc2136_test.py b/tests/dns_rfc2136_test.py
index ec424c6..72ea6d9 100644
--- a/tests/dns_rfc2136_test.py
+++ b/tests/dns_rfc2136_test.py
@@ -74,6 +74,27 @@
 
         self.auth.perform([self.achall])
 
+    def test_invalid_server_raises(self):
+        config = VALID_CONFIG.copy()
+        config["rfc2136_server"] = "example.com"
+        dns_test_common.write(config, self.config.rfc2136_credentials)
+
+        self.assertRaises(errors.PluginError,
+                          self.auth.perform,
+                          [self.achall])
+
+    @test_util.patch_display_util()
+    def test_valid_server_passes(self, unused_mock_get_utility):
+        config = VALID_CONFIG.copy()
+        dns_test_common.write(config, self.config.rfc2136_credentials)
+
+        self.auth.perform([self.achall])
+
+        config["rfc2136_server"] = "2001:db8:3333:4444:cccc:dddd:eeee:ffff"
+        dns_test_common.write(config, self.config.rfc2136_credentials)
+
+        self.auth.perform([self.achall])
+
 
 class RFC2136ClientTest(unittest.TestCase):