Service function chaining in a packet network

Service function chaining is a sequence of service function instances that traffic flows need to traverse through in order. Those service function instances are not required to reside on the direct path and traffic flow, but steered through network nodes. Service function instances and network nodes process the packets that carry a service function chain (SFC) header. The packets are encapsulated by a virtual network overlay header and forwarded through the service function instances in an SFC. The SFC header in specific format will prompt the network nodes to re-route the packets in the traffic flow using destination based forwarding or path based forwarding method in the packet network as well as an SDN controller and/or in-band control plane, and able to carry the metadata with the packets.