diff --git a/hooks/hooks.py b/hooks/hooks.py
index dcbbd54..98cdd34 100755
--- a/hooks/hooks.py
+++ b/hooks/hooks.py
@@ -48,7 +48,8 @@ from utils import (
     render_template,
     get_public_addr,
     assert_charm_supports_ipv6,
-    get_host_ip
+    get_host_ip,
+    get_network
 )
 
 hooks = Hooks()
@@ -84,6 +85,14 @@ def emit_cephconf():
         'ceph_public_network': config('ceph-public-network'),
         'ceph_cluster_network': config('ceph-cluster-network')
     }
+
+    if config('prefer-ipv6'):
+        network = get_network()
+        if not config('ceph-public-network'):
+            cephcontext['ceph_public_network'] = network
+        if not config('ceph-cluster-network'):
+            cephcontext['ceph_cluster_network'] = network
+
     # Install ceph.conf as an alternative to support
     # co-existence with other charms that write this file
     charm_ceph_conf = "/var/lib/charm/{}/ceph.conf".format(service_name())
diff --git a/hooks/utils.py b/hooks/utils.py
index 825c079..791dc54 100644
--- a/hooks/utils.py
+++ b/hooks/utils.py
@@ -98,3 +98,33 @@ def assert_charm_supports_ipv6():
     if lsb_release()['DISTRIB_CODENAME'].lower() < "trusty":
         raise Exception("IPv6 is not supported in the charms for Ubuntu "
                         "versions less than Trusty 14.04")
+
+
+def get_network(iface="eth0"):
+    try:
+        try:
+            import netifaces
+        except ImportError:
+            apt_install('python-netifaces')
+            import netifaces
+
+        try:
+            from netaddr import IPNetwork
+        except ImportError:
+            apt_install('python-netaddr', fatal=True)
+            from netaddr import IPNetwork
+
+        ipv6_address = get_ipv6_addr(iface)[0]
+        ifa_addrs = netifaces.ifaddresses(iface)
+
+        for ifaddr in ifa_addrs[netifaces.AF_INET6]:
+            if ipv6_address == ifaddr['addr']:
+                network = "{}/{}".format(ifaddr['addr'],
+                                         ifaddr['netmask'])
+                ip = IPNetwork(network)
+                return str(ip.network)
+
+    except ValueError:
+        raise Exception("Invalid interface '%s'" % iface)
+
+    raise Exception("No valid network found in interface '%s'" % iface)