Today I got this error message when restarting network service with # systemctl restart network.service or # service network restart:

Restarting network (via systemctl): Job for network.service failed. See 'systemctl status network.service' and 'journalctl -xn' for details.

Browsing around for a while, then found this solution:

# systemctl stop NetworkManager
# systemctl disable NetworkManager

After disabling NetworkManger, restarting network service succeeded.

Source:
– http://unix.stackexchange.com/questions/220750/centos-7-failed-to-bring-up-down-networking-configure-interface-for-a-trunk-in
– http://www.linuxquestions.org/questions/linux-newbie-8/centos-7-failed-to-bring-up-down-networking-configure-interface-for-a-trunk-interfa-4175550117/

If you want to jumpstart learning SDN without installing every single software on operating system, Srini Seetharaman has all-in-one VM that already installed with necessary SDN learning software.

The sofware and tools installed on the VM (listed by SDNhub.org):

• SDN Controllers: OpenDaylight, ONOS, RYU, Floodlight, Floodlight-OF1.3, POX, and Trema
• Example code for a hub, L2 learning switch, traffic tap, and other applications
• Open vSwitch 2.3.0 with support for Openflow 1.2, 1.3 and 1.4, and LINC switch
• Mininet to create and run example topologies
• Pyretic
• Wireshark 1.12.1 with native support for OpenFlow parsing
• JDK 1.8, Eclipse Luna, and Maven 3.3.3

These are the instruction steps:

1. Install VirtualBox or Vmware Player/Fusion
2. Install Putty and Xming (for Windows) or Xquartz (for Mac)
3. Download appliance from one of these link:
   http://yuba.stanford.edu/~srini/tutorial/SDN_tutorial_VM_32bit.ova
   http://yuba.stanford.edu/~srini/tutorial/SDN_tutorial_VM_64bit.ova
4. Import downloaded file (SDN_tutorial_VM_XXbit.ova) to VirtualBox or Vmware Player/Fusion
5. Start the VM (user/password: ubuntu/ubuntu)

Source:
– http://sdnhub.org/tutorials/sdn-tutorial-vm/
– http://yuba.stanford.edu/~srini/Beginners_OpenFlowTutorial_Meetup_June_2013.pptx