System Design and Workflow

Problem Description

The Service Chaining API specification proposes a Neutron port based solution for setting up a service chain. A specification on the system architecture and related API work flow is needed to guide the code design.

System Architecture

The following figure shows the generic architecture of the Port Chain Plugin. As shown in the diagram, Port Chain Plugin can be backed by different service providers such as OVS Driver and/or different types of SDN Controller Drivers. Through the “Common Driver API”, these different drivers can provide different implementations for the service chain path rendering. In the first release and deployment based on this release, we will only deliver codes for the OVS driver. In the next release, we can add codes to support multiple active drivers:

 Port Chain Plugin With Different Types of Drivers
|  +-----------------------------------------------------------+  |
|  |                        Port Chain API                     |  |
|  +-----------------------------------------------------------+  |
|  |                        Port Chain Database                |  |
|  +-----------------------------------------------------------+  |
|  |                        Driver Manager                     |  |
|  +-----------------------------------------------------------+  |
|  |                        Common Driver API                  |  |
|  +-----------------------------------------------------------+  |
|                                   |                             |
|  +------------+------------------------+---------------------+  |
|  | OVS Driver |   Controller Driver1   |  Controller Driver2 |  |
|  +------------+------------------------+---------------------+  |
        |                  |                         |
   +-----------+   +-----------------+      +-----------------+
   | OVS Agent |   | SDN Controller1 |      | SDN Controller2 |
   +-----------+   +-----------------+      +-----------------+

The second figure below shows the reference implementation architecture, which is through the OVS Driver path. The figure shows the components that will be added on the Neutron Server and the compute nodes to support this Neutron Based SFC functionality. As shown in the diagram, a new Port Chain Plugin will be added to the Neutron Server. The existing “OVS Driver” and “OVS Agent” will be extended to support the service chain functionality. The OVS Driver will communicate with each OVS Agent to program its OVS forwarding table properly so that a tenant’s traffic flow can be steered through the user defined sequence of Neutron ports to get the desired service treatment from the Service Function running on the VMs.

A separate OVS Driver and Agent specification will describe in more detail on the design consideration of the Driver, Agent, and how to set up the classification rules on the OVS to identify different flows and how to set up the OVS forwarding table. In the reference implementation, the OVS Driver communicates with OVS Agent through RPC to program the OVS. The communication between the OVS Agent and the OVS is through OVSDB/Openflow:

 Port Chain Plugin With OVS Driver
|  +-------------------------+  |
|  |    Port Chain API       |  |
|  +-------------------------+  |
|  |    Port Chain Database  |  |
|  +-------------------------+  |
|  |    Driver Manager       |  |
|  +-------------------------+  |
|  |    Common Driver API    |  |
|  +-------------------------+  |
|              |                |
|  +-------------------------+  |
|  |        OVS Driver       |  |
|  +-------------------------+  |
        |                |
   +-----------+   +-----------+
   | OVS Agent |   | OVS Agent |
   +-----------+   +-----------+

Port Chain Creation Workflow

The following example shows how the Neutron CLI commands may be used to create a port-chain consisting of a service VM vm1 and a service VM vm2. The user can be an Admin/Tenant or an Application built on top.

Traffic flow into the Port Chain will be from source IP address TCP port 23 to destination IP address TCP port 100. The flow needs to be treated by SF1 running on VM1 identified by Neutron port pair [p1, p2], SF2 running on VM2 identified by Neutron port pair [p3, p4], and SF3 running on VM3 identified by Neutron port pair [p5, p6].

The net1 should be created before creating Neutron port using existing Neutron API. The design has no restriction on the type of net1, i.e. it can be any type of Neutron network since SFC traffic will be tunneled transparently through the type of communication channels of net1. If the transport between vSwitches is VXLAN, then we will use that VXLAN tunnel (and NOT create another new tunnel) to transport the SFC traffic through. If the transport between vSwitches is Ethernet, then the SFC traffic will be transported through Ethernet. In other words, the SFC traffic will be carried over existing transport channel between vSwitches and the external transport channel between vSwitches is set up for net1 through existing Neutron API and ML2. The built-in OVS backend implements tunneling the original flow packets over VXLAN tunnel. The detailed outer VXLAN tunnel transport format and inner SFC flow format including how to leverage existing OVS’s support for MPLS label to carry chain ID will be described in the Port Chain OVS Driver and Agent specification. In the future we can add implementation of tunneling the SFC flow packets over flat L2 Ethernet or L3 IP network or GRE tunnel etc.

Boot service VMs and attach ports

Create Neutron ports on network net1:

openstack port create --network net1 p1
openstack port create --network net1 p2
openstack port create --network net1 p3
openstack port create --network net1 p4
openstack port create --network net1 p5
openstack port create --network net1 p6

Boot VM1 from Nova with ports p1 and p2 using two –nic options:

openstack server create --image xxx --nic port-id=p1-id --nic port-id=p2-id vm1 --flavor <image-flavour>

Boot VM2 from Nova with ports p3 and p4 using two –nic options:

openstack server create --image yyy --nic port-id=p3-id --nic port-id=p4-id vm2 --flavor <image-flavour>

Boot VM3 from Nova with ports p5 and p6 using two –nic options:

openstack server create --image zzz --nic port-id=p5-id --nic port-id=p6-id vm3 --flavor <image-flavour>

Alternatively, the user can create each VM with one VNIC and then attach another Neutron port to the VM:

openstack server create --image xxx --nic port-id=p1-id vm1
openstack server add port vm1 p2-id
openstack server create --image yyy --nic port-id=p3-id vm2
openstack server add port vm2 p4-id
openstack server create --image zzz --nic port-id=p5-id vm3
openstack server add port vm3 p6-id

Once the Neutron ports p1 - p6 exist, the Port Chain is created using the steps described below.

Create Flow Classifier

Create flow-classifier FC1 that matches on source IP address (ingress direction) and destination IP address (egress direction) with TCP connection, source port 23 and destination port 100:

openstack sfc flow classifier create \
 --ethertype IPv4 \
 --source-ip-prefix \
 --destination-ip-prefix \
 --protocol tcp \
 --source-port 23:23 \
 --destination-port 100:100 FC1


When using the (default) OVS driver, the --logical-source-port parameter is also required

Create Port Pair

Create port-pair PP1 with ports p1 and p2, port-pair PP2 with ports p3 and p4, port-pair PP3 with ports P5 and P6:

openstack sfc port pair create \
       --ingress=p1 \
       --egress=p2 PP1

openstack sfc port pair create \
       --ingress=p3 \
       --egress=p4 PP2

openstack sfc port pair create \
       --ingress=p5 \
       --egress=p6 PP3

Create Port Group

Create port-pair-group PG1 with port-pair PP1 and PP2, and port-pair-group PG2 with port-pair PP3:

openstack sfc port pair group create \
       --port-pair PP1 --port-pair PP2 PG1

openstack sfc port pair group create \
       --port-pair PP3 PG2

Create Port Chain

Create port-chain PC1 with port-group PG1 and PG2, and flow classifier FC1:

openstack sfc port chain create \
       --port-pair-group PG1 --port-pair-group PG2 --flow-classifier FC1 PC1

This will result in the Port chain driver being invoked to create the Port Chain.

The following diagram illustrates the code execution flow (not the exact codes) for the port chain creation:

PortChainAPIParsingAndValidation: create_port_chain
PortChainPlugin: create_port_chain
PortChainDbPlugin: create_port_chain
DriverManager: create_port_chain
portchain.drivers.OVSDriver: create_port_chain

The vSwitch Driver needs to figure out which switch VM1 is connecting with and which switch VM2 is connecting with (for OVS case, the OVS driver has that information given the VMs’ port info). As to the connection setup between the two vSwitches, it should be done through existing ML2 plugin mechanism. The connection between these two vSwitches should already be set up before the user initiates the SFC request. The service chain flow packets will be tunneled through the connecting type/technology (e.g. VXLAN or GRE) between the two vSwitches. For our reference code implementation, we will use VXLAN to show a complete data path setup. Please refer to the OVS Driver and OVS Agent specification for more detail info.