2.1. Quick Understand on VLCP Network Concepts

This tutorial is a quick describe on VLCP network concepts. You should read this first to have better understanding on these concepts. They should be easy to understand and look familiar for OpenStack users or users with experience on other SDN products.

2.1.1. Layer-2 Network (Ethernet)

With the standard network model [1], VLCP assumes you connect your virtual machines or docker containers with OpenvSwitch (or OVS) [2].

The physical view of the network can be described with the figure :Physical View of the Network.

Physical View of the Network

Physical View of the Network

In this figure, two physical servers are connected with an external network. On each server, two endpoints (virtual machines or docker containers) are connected to an OVS bridge with a Logical Port for each endpoint. A Physical Port which is connected to the external network (or the Physical Network) is also connected to the OVS bridge, connecting endpoints on this physical server with endpoints on other physical servers.

Physical Network refers to the external connections between physical servers. It must be a L2 connection, means that it can transfer Ethernet packets from one physical server to another. Usually it can be separated with VLAN-tag/VNI to isolate different type of traffic, making it possible to create multiple Logical Networks on the same Physical Network. In most cases, the Physical Network should be:

  • A physical network connecting the physical server with “trunk” port in the physical switches, so different Logical Networks can be isolated with VLAN tag
  • A overlay network connecting the physical servers with VXLAN tunnels. Different Logical Networks can be isolated with VXLAN ID (or VNI)

If necessary, there could be more than one Physical Networks on the same physical server.

Physical Port refers the OVS port connecting the OVS bridge with the Physical Network.

  • For VLAN networks, the port should be a physical NIC or bonding of NICs which directly connects to physical switches, and configured to “trunk” on physical switches
  • For VXLAN networks, the port should be a tunnel port created in OVS. The method to create this type of ports will be introduced in other documents.

Logical Port refers the OVS ports connecting the endpoints to the OVS bridge. It is usually a virtual device automatically created by external tools like libvirt or vlcp-docker-plugin. They act like access ports in traditional network and switches.

Each Logical Port has a corresponding Logical Network. A Logical Network is a virtual L2 network connecting endpoints from different physical servers with each other. Endpoints (or Logical Ports) in the same Logical Network can send Ethernet packets to and receive Ethernet packets from each other, while they can not send or receive Ethernet packets with endpoints in other Logical Network. You may consider a Logical Network as a standard Ethernet for endpoints.

With the isolation function of the Logcial Network, endpoints can be grouped into virtual networks, no matter what their physical locations are. Endpoints on different physical servers can access each other as if they are connected to the same L2 switch. At the same time, endpoints on the same physical server can be isolated as if they are connected to physical isolated networks. The logical view of the network looks like the figure :Logical View of the Network:

Logical View of the Network

Logical View of the Network

2.1.2. Logical Network and Subnet

VLCP network is functional even in pure Ethernet mode, in which case only MAC addresses are necessary to be configured on each Logical Port. But usually the network is used to transfer IP traffics, it is helpful to set IP and subnet configurations on the Logical Port. L2 connectivity is always available with or without subnet configurations.

IP configurations on a Logical Network is stored in a Subnet. Usually it contains CIDR and gateway of the network, but more advanced configurations are also available like static routes and DHCP options. Currently only IPv4 is supported.

A Logical Port is associated with both the Logical Network and the Subnet. The Logical Network association creates the L2 connectivity while the Subnet association affects functions related to IP addresses. Functions that need a Subnet configuration includes ARP proxy and embedded DHCP service.

2.1.3. Layer-3 (IP) Network and Routing

VLCP standard network model supports connecting different Logical Networks through L3 routing.

There are two types of networks in L3 routing: internal networks and external networks. External networks are Subnets with external gateways, the gateway set in Subnet of an external network should be IP address configured on external devices like physical routers. It should be accessible from the Logical Network VLAN or VXLAN. “Internal networks* are Subnets with internal gateways, the gateway address should not be any existed IP address in the network. VLCP SDN network will create a virtual router service for the networks as the default gateway of the internal networks.

Virtual router service with both internal networks and external networks forwards traffic to outer networks (Internet for example) through external networks. Correct routes for internal CIDRs should be configured in external gateways with static routes or technologies like OSPF, or use NAT (not yet supported).

Sometimes internal networks and external networks are in different Physical Networks, and not all server nodes have Physical Ports for Physical Network of the external network. For example, internal networks are connected through VXLAN, while external networks are using VLAN for isolation. In this situation, some forwarding nodes should be created to forward the traffic from internal networks to external networks. They are almost the same as other server nodes except a few configurations are modified. The figure :L3 Network with Forwarding Nodes shows the structure.

L3 Network with Forwarding Nodes

L3 Network with Forwarding Nodes

2.1.4. Network Settings Structure

To setup a new network, elements in the figure :Network Settings Structure should be created in order from top to bottom.

Network Settings Structure

Network Settings Structure



We should mention that VLCP is a full stack SDN controller which is:

  1. An asynchronous network programming framework with dynamic module mangement functions
  2. An OpenFlow controller framework friendly for extending
  3. A product-ready controller for standard virtual network environment, supported by default modules

Loading different modules can give VLCP completely different functions. In this document, we assume users would like to use the standard network model (also named as “ViperFlow” model) to implement a quick SDN environment highly compatible with traditional networks. You may also want to develope your own SDN controller, possibly supporting OpenFlow 1.0, or targeting physical OpenFlow switches. In that situation, you do not need to be bounded to this model. Refer to Development Guide for more informations on developing your own controller with VLCP framework, or learn more about the implementation details of the standard model.

[2]OpenvSwitch is a software implementation of OpenFlow switch with customized extensions. It should be familiar to experienced SDN users. Most virtual network environments and tools (libvirt, for example) support using OpenvSwitch to connect network endpoints to external networks. You may learn more about OpenvSwitch from the official web site (http://openvswitch.org/)