diff --git a/netsim/ansible/templates/initial/linux/ubuntu.j2 b/netsim/ansible/templates/initial/linux/ubuntu.j2
index 1b2fff83e..c33df24bf 100644
--- a/netsim/ansible/templates/initial/linux/ubuntu.j2
+++ b/netsim/ansible/templates/initial/linux/ubuntu.j2
@@ -158,9 +158,9 @@ network:
         transmit-hash-policy: encap3+4
 {%   else %}
     {{ l.ifname }}:
-{%   if l.mtu is defined %}
+{%     if l.mtu is defined %}
       mtu: {{ l.mtu }}
-{%   endif %}
+{%     endif %}
 {%   endif %}
 {%   if l.dhcp.client.ipv4|default(False) %}
       dhcp4: true
@@ -168,7 +168,7 @@ network:
 {%   if l.dhcp.client.ipv6|default(False) %}
       dhcp6: true
 {%   endif %}
-{%   for af in ('ipv4','ipv6') if af in l %}
+{%   for af in ('ipv4','ipv6') if af in l and l[af] is string %}
 {%     if loop.first %}
       addresses:
 {%     endif %}
diff --git a/netsim/ansible/templates/initial/linux/vanilla.j2 b/netsim/ansible/templates/initial/linux/vanilla.j2
index e55d2772d..db0e5a68a 100644
--- a/netsim/ansible/templates/initial/linux/vanilla.j2
+++ b/netsim/ansible/templates/initial/linux/vanilla.j2
@@ -33,13 +33,13 @@ ip -6 addr add {{ loopback.ipv6 }} dev lo
 {{     create_bond_dev(l,node_provider) }}
 {%   endif %}
 ip link set dev {{ l.ifname }} up
-{% if l.ipv4 is defined %}
+{% if l.ipv4 is defined and l.ipv4 is string %}
 set +e
 ip addr del {{ l.ipv4 }} dev {{ l.ifname }} 2>/dev/null
 set -e
 ip addr add {{ l.ipv4 }} dev {{ l.ifname }}
 {% endif %}
-{% if l.ipv6 is defined %}
+{% if l.ipv6 is defined and l.ipv6 is string %}
 sysctl -w net.ipv6.conf.{{ l.ifname }}.disable_ipv6=0
 set +e
 ip -6 addr del {{ l.ipv6 }} dev {{ l.ifname }} 2>/dev/null