diff --git a/app/authentication/auth.py b/app/authentication/auth.py
index f7866a943..d24153bcd 100644
--- a/app/authentication/auth.py
+++ b/app/authentication/auth.py
@@ -1,14 +1,13 @@
+from ipaddress import IPv4Address, IPv4Network
+
 from flask import request, _request_ctx_stack, current_app, g
+from notifications_python_client.authentication import decode_jwt_token, get_token_issuer
+from notifications_python_client.errors import TokenDecodeError, TokenExpiredError, TokenIssuerError
 from sqlalchemy.exc import DataError
 from sqlalchemy.orm.exc import NoResultFound
 
-from notifications_python_client.authentication import decode_jwt_token, get_token_issuer
-from notifications_python_client.errors import TokenDecodeError, TokenExpiredError, TokenIssuerError
-
 from app.dao.services_dao import dao_fetch_service_by_id_with_api_keys
 
-from ipaddress import IPv4Interface, ip_address
-
 
 class AuthError(Exception):
     def __init__(self, message, code):
@@ -58,36 +57,38 @@ def restrict_ip_sms():
         # Counting backwards and look at the IP at the 3rd last hop - hence, hop(end-3)
         ip_route = request.headers.get("X-Forwarded-For")
         ip_list = ip_route.split(',')
-        if len(ip_list) >= 3:
-            inbound_ip = ip_list[len(ip_list) - 3]
+
         current_app.logger.info("Inbound sms ip route list {}"
                                 .format(ip_route))
+        if len(ip_list) >= 3:
+            inbound_ip = IPv4Address(ip_list[len(ip_list) - 3])
 
-    # IP whitelist
-    allowed_ips = current_app.config.get('SMS_INBOUND_WHITELIST')
-    allowed = False
+            # IP whitelist
+            allowed_ips = current_app.config.get('SMS_INBOUND_WHITELIST')
 
-    for allowed_ip in allowed_ips:
-        masked_bits = ''
-        if (len(allowed_ip.split('/')) > 1):
-            masked_bits = allowed_ip.split('/')[1]
-        inbound_ip_str = inbound_ip + '/' + masked_bits
-        if IPv4Interface(allowed_ip).network == IPv4Interface(inbound_ip_str).network:
-            allowed = True
-            # return
-            break
-        # else:
-            # raise AuthError('Unknown source IP address from the SMS provider', 403)
+            allowed = any(
+                inbound_ip in IPv4Network(allowed_ip)
+                for allowed_ip in allowed_ips
+            )
 
-    current_app.logger.info({
-        'message': 'Inbound sms ip address',
-        'log_contents': {
-            'passed': allowed,
-            'ip_address': ip
-        }
-    })
+            # if allowed:
+            #    return
+            # else:
+            #    raise AuthError('Unknown source IP address from the SMS provider', 403)
 
-    return
+            current_app.logger.info({
+                'message': 'Inbound sms ip address',
+                'log_contents': {
+                    'passed': allowed,
+                    'ip_address': ip
+                }
+            })
+            return
+
+    current_app.logger.error('Traffic from unknown source or route, X-Forwarded-For="{}"'.format(
+        request.headers.get("X-Forwarded-For"))
+    )
+    # raise AuthError('Traffic from unknown source or route', 403)
 
 
 def requires_admin_auth():
diff --git a/tests/app/authentication/test_authentication.py b/tests/app/authentication/test_authentication.py
index 000d08211..15eb7f2ec 100644
--- a/tests/app/authentication/test_authentication.py
+++ b/tests/app/authentication/test_authentication.py
@@ -313,7 +313,7 @@ def __create_token(service_id):
 def restrict_ip_sms_app():
     app = flask.Flask(__name__)
     app.config['TESTING'] = True
-    app.config['SMS_INBOUND_WHITELIST'] = ['111.111.111.111/32', '200.200.200.200/24']
+    app.config['SMS_INBOUND_WHITELIST'] = ['111.111.111.111/32', '200.200.200.0/24']
     blueprint = flask.Blueprint('restrict_ip_sms_app', __name__)
 
     @blueprint.route('/')
@@ -364,7 +364,7 @@ def test_illegitimate_ips(restrict_ip_sms_app):
     assert exc_info.value.short_message == 'Unknown IP route not from known SMS provider'
 
 
-def test_allow_valid_ips_24bits(restrict_ip_sms_app):
+def test_allow_valid_ips_bits(restrict_ip_sms_app):
     # Test an address that match the first 24 bits only
     response = restrict_ip_sms_app.get(
         path='/',