diff --git a/data/hostname/kafka1.internal.softwareheritage.org.yaml b/data/hostname/kafka1.internal.softwareheritage.org.yaml
index 86869552..5b11f0de 100644
--- a/data/hostname/kafka1.internal.softwareheritage.org.yaml
+++ b/data/hostname/kafka1.internal.softwareheritage.org.yaml
@@ -1,52 +1,56 @@
 ---
 networks:
   ens1f0np0:
     type: manual
-    mtu: 9000
+    extras:
+      mtu: "9000"
   ens1f1np1:
     type: manual
-    mtu: 9000
+    extras:
+      mtu: "9000"
   bond0:
     type: manual
-    mtu: 9000
     extras:
+      mtu: "9000"
       bond-miimon: 100
       bond-mode: 802.3ad
       bond-xmit_hash_policy: layer3+4
       bond-slaves: ens1f0np0 ens1f1np1
       bond-lacp-rate: 1
   vlan440:
     type: private
     address: 192.168.100.201
     netmask: 24
     gateway: 192.168.100.1
+    mtu: "9000"
     extras:
       vlan-raw-device: bond0
   vlan1300:
     type: static
     address: 128.93.166.48
     netmask: 26
     gateway: 128.93.166.62
+    mtu: "9000"
     extras:
       vlan-raw-device: bond0
 
 backups::exclude:
   - srv/kafka
 
 swh::apt_config::enable_non_free: true
 packages:
   - intel-microcode
   - vlan
   - ifenslave
 
 swh::apt_config::backported_packages:
   buster:
     - linux-image-amd64
     - linux-headers-amd64
     - libnvpair1linux
     - libuutil1linux
     - libzfs2linux
     - libzpool2linux
     - zfs-dkms
     - zfsutils-linux
     - zfs-zed
diff --git a/data/hostname/kafka2.internal.softwareheritage.org.yaml b/data/hostname/kafka2.internal.softwareheritage.org.yaml
index e1e51e8d..4f8b7288 100644
--- a/data/hostname/kafka2.internal.softwareheritage.org.yaml
+++ b/data/hostname/kafka2.internal.softwareheritage.org.yaml
@@ -1,52 +1,56 @@
 ---
 networks:
   ens1f0np0:
     type: manual
-    mtu: 9000
+    extras:
+      mtu: "9000"
   ens1f1np1:
     type: manual
-    mtu: 9000
+    extras:
+      mtu: "9000"
   bond0:
     type: manual
-    mtu: 9000
     extras:
+      mtu: "9000"
       bond-miimon: 100
       bond-mode: 802.3ad
       bond-xmit_hash_policy: layer3+4
       bond-slaves: ens1f0np0 ens1f1np1
       bond-lacp-rate: 1
   vlan440:
     type: private
     address: 192.168.100.202
     netmask: 24
     gateway: 192.168.100.1
+    mtu: "9000"
     extras:
       vlan-raw-device: bond0
   vlan1300:
     type: static
     address: 128.93.166.49
     netmask: 26
     gateway: 128.93.166.62
+    mtu: "9000"
     extras:
       vlan-raw-device: bond0
 
 backups::exclude:
   - srv/kafka
 
 swh::apt_config::enable_non_free: true
 packages:
   - intel-microcode
   - vlan
   - ifenslave
 
 swh::apt_config::backported_packages:
   buster:
     - linux-image-amd64
     - linux-headers-amd64
     - libnvpair1linux
     - libuutil1linux
     - libzfs2linux
     - libzpool2linux
     - zfs-dkms
     - zfsutils-linux
     - zfs-zed
diff --git a/data/hostname/kafka3.internal.softwareheritage.org.yaml b/data/hostname/kafka3.internal.softwareheritage.org.yaml
index ae56c932..5fbaf7ce 100644
--- a/data/hostname/kafka3.internal.softwareheritage.org.yaml
+++ b/data/hostname/kafka3.internal.softwareheritage.org.yaml
@@ -1,52 +1,56 @@
 ---
 networks:
   ens1f0np0:
     type: manual
-    mtu: 9000
+    extras:
+      mtu: "9000"
   ens1f1np1:
     type: manual
-    mtu: 9000
+    extras:
+      mtu: "9000"
   bond0:
     type: manual
-    mtu: 9000
     extras:
+      mtu: "9000"
       bond-miimon: 100
       bond-mode: 802.3ad
       bond-xmit_hash_policy: layer3+4
       bond-slaves: ens1f0np0 ens1f1np1
       bond-lacp-rate: 1
   vlan440:
     type: private
     address: 192.168.100.203
     netmask: 24
     gateway: 192.168.100.1
+    mtu: "9000"
     extras:
       vlan-raw-device: bond0
   vlan1300:
     type: static
     address: 128.93.166.50
     netmask: 26
     gateway: 128.93.166.62
+    mtu: "9000"
     extras:
       vlan-raw-device: bond0
 
 backups::exclude:
   - srv/kafka
 
 swh::apt_config::enable_non_free: true
 packages:
   - intel-microcode
   - vlan
   - ifenslave
 
 swh::apt_config::backported_packages:
   buster:
     - linux-image-amd64
     - linux-headers-amd64
     - libnvpair1linux
     - libuutil1linux
     - libzfs2linux
     - libzpool2linux
     - zfs-dkms
     - zfsutils-linux
     - zfs-zed
diff --git a/data/hostname/kafka4.internal.softwareheritage.org.yaml b/data/hostname/kafka4.internal.softwareheritage.org.yaml
index 5ca096c8..692283b0 100644
--- a/data/hostname/kafka4.internal.softwareheritage.org.yaml
+++ b/data/hostname/kafka4.internal.softwareheritage.org.yaml
@@ -1,52 +1,56 @@
 ---
 networks:
   ens1f0np0:
     type: manual
-    mtu: 9000
+    extras:
+      mtu: "9000"
   ens1f1np1:
     type: manual
-    mtu: 9000
+    extras:
+      mtu: "9000"
   bond0:
     type: manual
-    mtu: 9000
     extras:
+      mtu: "9000"
       bond-miimon: 100
       bond-mode: 802.3ad
       bond-xmit_hash_policy: layer3+4
       bond-slaves: ens1f0np0 ens1f1np1
       bond-lacp-rate: 1
   vlan440:
     type: private
     address: 192.168.100.204
     netmask: 24
     gateway: 192.168.100.1
+    mtu: "9000"
     extras:
       vlan-raw-device: bond0
   vlan1300:
     type: static
     address: 128.93.166.51
     netmask: 26
     gateway: 128.93.166.62
+    mtu: "9000"
     extras:
       vlan-raw-device: bond0
 
 backups::exclude:
   - srv/kafka
 
 swh::apt_config::enable_non_free: true
 packages:
   - intel-microcode
   - vlan
   - ifenslave
 
 swh::apt_config::backported_packages:
   buster:
     - linux-image-amd64
     - linux-headers-amd64
     - libnvpair1linux
     - libuutil1linux
     - libzfs2linux
     - libzpool2linux
     - zfs-dkms
     - zfsutils-linux
     - zfs-zed