Introduction to VXLAN
Introduce the definition, purpose and benefits of VXLAN.
definition
RFC7348 defines the VLAN extension scheme VXLAN (Virtual eXtensible Local Area Network). VXLAN uses MAC in UDP (User Datagram Protocol) encapsulation method and is a network virtualization technology in NVO3 (Network Virtualization over Layer 3).
Purpose
As one of the core technologies of cloud computing, server virtualization has been increasingly recognized and deployed for its advantages of significantly reducing IT costs, improving business deployment flexibility, and reducing operation and maintenance costs.
Figure 1 Schematic diagram of server virtualization
As shown in Figure 1 , one server can virtualize multiple virtual machines, and one virtual machine is equivalent to one host. The number of hosts has changed by orders of magnitude, which has also brought the following problems to the virtual network:
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The size of the virtual machine is limited by network specifications
In a traditional Layer 2 network environment, data packets are forwarded at Layer 2 by querying the MAC address table, and the capacity of the MAC address table limits the number of virtual machines.
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Network isolation capability limitations
The current mainstream network isolation technology is VLAN, which has the following limitations when deployed in large-scale virtualized networks:- Since the VLAN Tag field defined in IEEE 802.1Q has only 12 bits and can only represent 4096 VLANs, it cannot meet the needs of identifying a large number of tenants or tenant groups in large Layer 2 networks.
- VLANs in traditional Layer 2 networks cannot meet the needs of dynamic network adjustment.
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The scope of virtual machine migration is limited by network architecture
After the virtual machine is started, the virtual machine may need to be migrated to a new server due to server resource issues (such as high CPU, insufficient memory, etc.). In order to ensure that services are not interrupted during virtual machine migration, it is necessary to ensure that the IP address of the virtual machine remains unchanged. This requires the business network to be a Layer 2 network, and the network itself is required to have multi-path redundant backup and reliability.
For large layer 2 networks, the introduction of VXLAN solves the above problems well:
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The size of the virtual machine is limited by network specifications.
VXLAN encapsulates the data packets sent by the virtual machine in UDP, and uses the IP and MAC address of the physical network as the outer header for encapsulation, and only displays the encapsulated parameters to the network. Therefore, the demand for MAC address specifications in large Layer 2 networks is greatly reduced.
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Limitations on network isolation capabilities
VXLAN introduces a user identification similar to VLAN ID, called VXLAN Network Identifier VNI (VXLAN Network Identifier), which consists of 24 bits and supports up to 16M VXLAN segments, thereby satisfying a large number of user identifications.
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The scope of virtual machine migration is limited by network architecture
VXLAN extends the Layer 2 network by using MAC in UDP encapsulation, encapsulating Ethernet packets on top of IP packets, and transmitting them through the network through routing, without paying attention to the MAC address of the virtual machine. Moreover, the routing network has no network structure restrictions and has large-scale expansion capabilities, fault self-healing capabilities, and load balancing capabilities. With routed networks, virtual machine migration is not limited by network architecture.
benefit
With the rapid development of data centers implementing server virtualization on physical network infrastructure, VXLAN, one of the NVO3 technologies:
- The 24-bit VNI can support network isolation of up to 16M VXLAN segments. User isolation and identification are no longer restricted, and can satisfy a large number of tenants.
- Except for VXLAN network edge devices, other devices in the network do not need to identify the MAC address of the virtual machine, which reduces the pressure of MAC address learning on the device and improves device performance.
- By using MAC in UDP encapsulation to extend the Layer 2 network, the physical network and the virtual network are decoupled. Tenants can plan their own virtual networks without considering the restrictions of the physical network IP address and broadcast domain, which greatly reduces the difficulty of network management. .