commit b55eb2cda2f4fe0a2ae40b5730b5fcd356a3e7d6 (HEAD -> curtin-centos)
Author: Ryan Harper <ryan.harper@canonical.com>
Date:   Thu Jun 15 15:09:17 2017 -0500

    sysconfig: enable mtu set per subnet, including ipv6 mtu

diff --git a/cloudinit/net/sysconfig.py b/cloudinit/net/sysconfig.py
index b81e57a..ca710ec 100644
--- a/cloudinit/net/sysconfig.py
+++ b/cloudinit/net/sysconfig.py
@@ -271,6 +271,7 @@ class Renderer(renderer.Renderer):
 
         # modifying base values according to subnets
         for i, subnet in enumerate(subnets, start=len(iface_cfg.children)):
+            mtu_key = 'MTU'
             subnet_type = subnet.get('type')
             if subnet_type == 'dhcp6':
                 iface_cfg['IPV6INIT'] = True
@@ -290,7 +291,11 @@ class Renderer(renderer.Renderer):
                 # if iface_cfg['BOOTPROTO'] == 'none':
                 #    iface_cfg['BOOTPROTO'] = 'static'
                 if subnet_is_ipv6(subnet):
+                    mtu_key = 'IPV6_MTU'
                     iface_cfg['IPV6INIT'] = True
+                if 'mtu' in subnet:
+                    iface_cfg[mtu_key] = subnet['mtu']
+
             elif subnet_type == 'manual':
                 iface_cfg['ONBOOT'] = False
             else: