diff --git a/global_config.yaml b/global_config.yaml
index f6213ca..025bd60 100644
--- a/global_config.yaml
+++ b/global_config.yaml
@@ -11,6 +11,7 @@
 flavor_disk: 5
 nova_timeout: 300
 external_network: 'public'
+custom_mtu: 'defaut' # 'default' or some value like 8950
 iperf_prep_string: "sudo /bin/bash -c 'echo \"91.189.88.161        archive.ubuntu.com\" >> /etc/hosts'"
 internet_at_vms: 'true' # whether Internet is present at OpenStack VMs and iperf can be installed with apt
 iperf_deb_package_dir_path: '/opt/packages/'