VNF Forwarding Graph

VNF Forwarding Graph

VNF Forwarding Graph or VNFFG feature in Tacker is used to orchestrate and manage traffic through VNFs. In short, abstract VNFFG TOSCA definitions are rendered into Service Function Chains (SFCs) and Classifiers. The SFC makes up an ordered list of VNFs for traffic to traverse, while the classifier decides which traffic should go through them.

Similar to how VNFs are described by VNFDs, VNFFGs are described by VNF Forwarding Graph Descriptors (VNFFGD). Please see the devref guide on VNFFGD to learn more about how a VNFFGD is defined.

VNFFG can be instantiated from VNFFGD or directly from VNFFGD template by separate Tacker commands. This action will build the chain and classifier necessary to realize the VNFFG.


VNFFG with OpenStack VIM relies on Neutron Networking-sfc to create SFC and Classifiers. Therefore it is required to install networking-sfc project in order to use Tacker VNFFG. Networking-sfc also requires at least OVS 2.5 .0, so also ensure that is installed. See the full Networking-sfc guide.

A simple example of a service chain would be one that forces all traffice from HTTP client to HTTP server to go through VNFs that was created by VNFFG.

Firstly, HTTP client and HTTP server must be launched.

net_id=$(openstack network list | grep net0 | awk '{print $2}')

openstack server create --flavor m1.tiny --image cirros-0.3.5-x86_64-disk \
--nic net-id=$net_id http_client

openstack server create --flavor m1.tiny --image cirros-0.3.5-x86_64-disk \
--nic net-id=$net_id http_server

Creating the VNFFGD

Once OpenStack/Devstack along with Tacker has been successfully installed, deploy a sample VNFFGD template such as the one here.


A current constraint of the Forwarding Path policy match criteria is to include the network_src_port_id, such as:

  type: ACL
  - network_src_port_id: 640dfd77-c92b-45a3-b8fc-22712de480e1
  - destination_port_range: 80-1024
  - ip_proto: 6
  - ip_dst_prefix:

You can get network_src_port_id and IP destination address through OpenStack commands like bellow:

client_ip=$(openstack server list | grep http_client | \
 grep -Eo '[0-9]+\.[0-9]+\.[0-9]+\.[0-9]+')

network_source_port_id=$(openstack port list | grep $client_ip | awk '{print $2}')

ip_dst=$(openstack server list | grep http_server | \
 grep -Eo '[0-9]+\.[0-9]+\.[0-9]+\.[0-9]+')

This is required due to a limitation of Neutron networking-sfc and only applies to an OpenStack VIM.

Tacker provides the following CLI to create a VNFFGD:

tacker vnffgd-create --vnffgd-file <vnffgd-file> <vnffgd-name>

Creating the VNFFG

To create a VNFFG, you must have first created VNF instances of the same VNFD types listed in the VNFFGD. Failure to do so will result in error when trying to create a VNFFG. Note, the VNFD you define must include the same Connection Point definitions as the ones you declared in your VNFFGD.

tacker vnfd-create --vnfd-file tosca-vnffg-vnfd1.yaml VNFD1
tacker vnf-create --vnfd-name VNFD1 VNF1

tacker vnfd-create --vnfd-file tosca-vnffg-vnfd2.yaml VNFD2
tacker vnf-create --vnfd-name VNFD2 VNF2

Refer the ‘Getting Started’ link below on how to create a VNFD and deploy 2 VNFs: VNF1 and VNF2.

Tacker provides the following CLI to create VNFFG from VNFFGD:

tacker vnffg-create --vnffgd-name <vnffgd-name> \
       --vnf-mapping <vnf-mapping> --symmetrical <boolean> <vnffg-name>

or you can create directly VNFFG from vnffgd template without initiating VNFFGD.

tacker vnffg-create --vnffgd-template <vnffgd-template> \
   --vnf-mapping <vnf-mapping> --symmetrical <boolean> <vnffg-name>

If you use a parameterized vnffg template:

tacker vnffg-create --vnffgd-name <vnffgd-name> \
   --param-file <param-file> --vnf-mapping <vnf-mapping> \
   --symmetrical <boolean> <vnffg-name>


  • vnffgd-name - VNFFGD to use to instantiate this VNFFG
  • param-file - Parameter file in Yaml.
  • vnf-mapping - Allows a list of logical VNFD to VNF instance mapping
  • symmetrical - True/False

VNF Mapping is used to declare which exact VNF instance to be used for each VNF in the Forwarding Path. The following command would list VNFs in Tacker and then map each VNFD defined in the VNFFGD Forwarding Path to the desired VNF instance:

tacker vnf-list

| id                                   | name | mgmt_url                  | status | vim_id                               | vnfd_id                              |
| 7168062e-9fa1-4203-8cb7-f5c99ff3ee1b | VNF2 | {"VDU1": ""}   | ACTIVE | 0e70ec23-6f32-420a-a039-2cdb2c20c329 | ea842879-5a7a-4f29-a8b0-528b2ad3b027 |
| 91e32c20-6d1f-47a4-9ba7-08f5e5effe07 | VNF1 | {"VDU1": ""}   | ACTIVE | 0e70ec23-6f32-420a-a039-2cdb2c20c329 | 27795330-62a7-406d-9443-2daad76e674b |

tacker vnffg-create --vnffgd-name myvnffgd --vnf-mapping \
   VNFD1:'91e32c20-6d1f-47a4-9ba7-08f5e5effe07',VNF2:'7168062e-9fa1-4203-8cb7-f5c99ff3ee1b' myvnffg

Alternatively, if no vnf-mapping is provided then Tacker VNFFG will attempt to search for VNF instances derived from the given VNFDs in the VNFFGD. If multiple VNF instances exist for a given VNFD, the VNF instance chosen to be used in the VNFFG is done at random.

The symmetrical argument is used to indicate if reverse traffic should also flow through the path. This creates an extra classifier to ensure return traffic flows through the chain in a reverse path, otherwise this traffic routed normally and does not enter the VNFFG.


Enabling symmetrical is not currently supported by the OpenStack VIM driver

Parameters for VNFFGD template

Similar to TOSCA VNFD template, any value of VNFFGD template can be parameterized. Once parameterized different values can be passed while instantiating the forwarding graph using the same VNFFGD template. The value of a parameterized attribute can be specified like {get_input foo} in the TOSCA VNFFGD template. The corresponding param-file in the following YAML format can be provided in the vnffg-create command,

  foo: bar

VNFFG command with parameter file:

tacker vnffg-create --vnffgd-name vnffgd-param --vnf-mapping VNFD1:'91e32c20-6d1f-47a4-9ba7-08f5e5effe07',\
VNFD2:'7168062e-9fa1-4203-8cb7-f5c99ff3ee1b' --param-file vnffg-param-file.yaml myvnffg

See VNFFGD template samples with parameter support.

Viewing a VNFFG

A VNFFG once created is instantiated as multiple sub-components. These components include the VNFFG itself, which relies on a Network Forwarding Path (NFP). The NFP is then composed of a Service Function Chain (SFC) and a Classifier. The main command to view a VNFFG is ‘tacker vnffg-show, however there are several commands available in order to view the sub-components for a rendered VNFFG:

tacker nfp-list
tacker nfp-show <nfp id>
tacker chain-list
tacker chain-show <chain id>
tacker classifier-list
tacker classifier-show <classifier id>

Known Issues and Limitations

  • Match criteria requires ‘network_src_port_id’
  • Only one Forwarding Path allowed per VNFFGD
  • Matching on criteria with postfix ‘name’ does not work, for example ‘network_name’
  • NSH attributes not yet supported
  • Symmetrical is not supported by driver yet
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