Transformation from Legacy Network to SDN
Moving towards SDN:
As we see the traditional network, each network device like router and switch has its control plane and data plane, and each device runs control software like operating system which includes Routing and Switching features like BGP, OSPF, EIGRP, Spanning-Tree, LACP etc. These end device runs these protocol individually to build network and forward traffic.
These integration between Software and Hardware limits the scalability of the network because each device do not have full view of network.
In order to dis-aggregate the control plane and data plane, we used a method called SDN which has single control plane software called SDN controller and multiple bare metal SDN enabled Switches (example open flow switches).
Core Features of SDN:
Following are the core features of SDN, these are discussed below.
Programmable Fabric: SDN makes the fabric programmable which means it can direct the traffic, Apply filters to packet, determine the least cost path etc. All these can be done by centralized controller.
Southbound Protocol: South bound protocol are the protocols through which Controller communicates with switches and routers to manipulate and optimize the traffic flow on programmable fabric. Example of south bound protocol is OPEN FLOW. An SDN controller can support various south bound protocol and various version of OPEN FLOW.
External API Support: With the help of External API support and SDN platform can able to communicate to various orchestration and cloud environment like VMware vSphere, OpenStack etc. Example VMware vSphere will talk to SDN to extend vDS switch from virtual environment to physical underlay network.
Central Monitoring and Network Discovery: As SDN controller has full view of network, it can discover all the physical link along with network devices. It can also present the map of all connected devices (host) connected to network. SDN also support monitoring and management protocol like syslog , snmp and also support API integration with third party NMS.
Network Performance: network performance depends how SDN controller populates flow table to SDN enabled switch. Some SDN controller pre-populates the flow tables to avoid delay. But as a first packet to SDN enabled network, if SDN enabled device does not find any entry in flow table, it will send packet to SDN controller to find out where packet needs to get forwarded. Once the details are derived, its entry is populated to flow table of SDN switches.
High-Availability: In order to provide the HA features SDN controllers must be installed in clusters which further supports scalability to add more SDN controller to provide load balancing and availability.
Following are the SDN components which are given below:
- SDN Controller: Can be one or more than one but in clusters
- SDN enabled switches: Uses southbound API to talk to SDN controller.
You can image the SDN controller as supervisor module (brain) of switch.