diff --git a/cloudinit/net/sysconfig.py b/cloudinit/net/sysconfig.py
index 8bd7e88..810b283 100644
--- a/cloudinit/net/sysconfig.py
+++ b/cloudinit/net/sysconfig.py
@@ -754,7 +754,16 @@ class Renderer(renderer.Renderer):
         # Distros configuring /etc/sysconfig/network as a file e.g. Centos
         if sysconfig_path.endswith('network'):
             util.ensure_dir(os.path.dirname(sysconfig_path))
-            netcfg = [_make_header(), 'NETWORKING=yes']
+            netcfg = []
+            for line in util.load_file(sysconfig_path, quiet=True).split('\n'):
+                if 'cloud-init' in line:
+                    break
+                if not line.startswith(('NETWORKING=',
+                                        'IPV6_AUTOCONF=',
+                                        'NETWORKING_IPV6=')):
+                    netcfg.append(line)
+            # Now generate the cloud-init portion of sysconfig/network
+            netcfg.extend([_make_header(), 'NETWORKING=yes'])
             if network_state.use_ipv6:
                 netcfg.append('NETWORKING_IPV6=yes')
                 netcfg.append('IPV6_AUTOCONF=no')
diff --git a/tests/unittests/test_net.py b/tests/unittests/test_net.py
index 1306a0f..a931a3e 100644
--- a/tests/unittests/test_net.py
+++ b/tests/unittests/test_net.py
@@ -1483,7 +1483,6 @@ pre-down route del -net 10.0.0.0/8 gw 11.0.0.1 metric 3 || true
                 BOOTPROTO=none
                 DEVICE=bond0
                 DHCPV6C=yes
-                IPV6_AUTOCONF=no
                 IPV6INIT=yes
                 MACADDR=aa:bb:cc:dd:ee:ff
                 ONBOOT=yes