Underlay network
Ethernet was designed from the very beginning to be a distributed network. There is no central control node. Each device in the network learns the reachability information of the network through protocol transmission, and each device decides how to forward it. This leads directly to the lack of a holistic concept and the inability to regulate traffic from the perspective of the entire network. To complete the intercommunication between all network devices, it is necessary to use a common language. This is the network protocol. RFC is the law of the network protocol, which is equivalent to international law. Each equipment supplier’s compliance with international law basically guarantees the entire network world. normal operation. Underlay is the network of the current data center network basic forwarding architecture. As long as any two points on the data center network are reachable, it refers to the physical basic layer . We can improve the Underlay network through the technical improvement of the physical network equipment itself, the expansion of the number of equipment, the scale of bandwidth, etc., which include all existing traditional network technologies.
Overlay network
In the field of network technology, Overlay is a virtualization technology model superimposed on the network architecture. Its general framework is to realize the bearer application on the network without large-scale modification of the basic network, and can be separated from other network services . It is a virtual network built on an existing network, and an overlay network is composed of logical nodes and logical links. The overlay network has an independent control and forwarding plane, and the physical network is transparent to the terminal system connected to the overlay edge device . By deploying an overlay network, the physical network can be extended to the cloud and virtualization in depth, and the cloud resource pooling ability can get rid of the constraints of the physical network, which is the key to achieving cloud-network integration. The Overlay network is also a network, but a network built on the Underlay network. The nodes of the Overlay network communicate through virtual or logical links. Each virtual or logical link corresponds to a path of the Underlay network, which is composed of multiple links that connect back and forth.
Overlay technology can be divided into three categories: Network Overlay, Host Overlay and Hybrid Overlay. Network Overlay refers to network construction and expansion of edge network equipment through control protocols, which is the overlay network technology mentioned in this article. Overlay network technologies are diverse, and tunnel technologies such as TRILL, VxLan, GRE, and NVGRE are generally used. TRILL (Transparent Interconnection of Lots of Links) technology is a new type of ring network technology promoted by telecom equipment manufacturers; NVGRE (Network Virtualization using Generic Routing Encapsulation) and STT (Stateless Transport Tunneling Protocol) are the overlay technologies promoted by IT manufacturers; and everyone is very familiar with it Tunnel-based encapsulation technology such as VXLAN (Virtual eXtensible LAN). Since these are also new protocols, they need to be upgraded to support existing network equipment. The location of application deployment in the overlay network will not be restricted. The network equipment can be plug and play, automatically configured and issued, and run automatically. Overlay network business changes, the basic network is not aware, and there is very little modification of the traditional network. The most important thing is Both virtual machines and physical servers can be connected to the Overlay network.
The Overlay network and the Underlay network are independent of each other. The Overlay network uses the Underlay network to transfer messages point-to-point, and how the message is delivered to the destination node of the Overlay network depends entirely on the control plane and data plane of the Underlay network. The message enters the Overlay network. The processing of outgoing nodes (such as discarding and forwarding) is completely determined by the encapsulation protocol of the Overlay network. Since it is a tunneling technology, it is necessary to add some headers to the original message, which will undoubtedly increase the network forwarding burden, and transmit more "useless" byte messages, which will reduce network performance. Underlay is the data The ultimate form of central network development. In addition, the overlay network is not completely decoupled from the physical network, and a lot of manual configuration is still required on servers and network equipment. The deployment of the overlay network does not reduce maintainability, but increases the burden of operation and maintenance. Overlay network and Underlay network are actually not new concepts. For example, in traditional networks, L3VPN, flexible QINQ, MACinMAC and other functions are all tunnel technologies. The functions of these protocols are very similar to those of Overlay, except that the ones used by Overlay The new agreement considers more virtual machine migration and mobility, and the definition of the new agreement is more abundant and reasonable. Overlay network technology fully takes into account the practical problems of data center networks. The existing network is difficult to switch to the SDN network at once. The network is completely composed of the controller and the Underlay network, and the forwarding plane and the control plane are completely decoupled. The Overlay network can make full use of the existing physical network to completely virtualize a logical network, which can fully meet the purpose of any migration of virtual machines in the network without wasting existing network resources. It is in the SDN network and traditional A compromise between the networks, the future of the network must be the Underlay plus controller.
The data center network is divided into two parts: Underlay and Overlay. It is generated under the background of data center virtualization. Although the Overlay network is more important at present, it also needs the Underlay network, and the Underlay network is essential. For a period of time, the two network forms will coexist for a long time. As SDN technology matures, Overlay networks may slowly withdraw from the stage of history, and the controller will take over the network entirely.
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Original link: https://blog.csdn.net/zjc801blog/article/details/54289683