DCI solution Selection and Design (1)

In the traditional Data Center Server area network design, the L2 network is usually limited to the network aggregation layer. By configuring VLANs for cross-aggregation switches, the L2 network can be extended to multiple access switches. This solution provides flexible scalability for the server network access layer. In recent years, high-availability cluster technology and dynamic migration technology of virtual servers (such as VMware's VMotion) have been widely used in data center Disaster Tolerance and computing resource allocation, these two technologies not only require large L2 network access within the Data Center, but also require a wide range of L2 network expansion (DCI: Data Center Interconnection) between the Data centers ).

I. Interconnection between data centers

As shown in 1, three interconnection links are usually deployed between data centers. Each interconnection link carries different data and implements different functions. These three links are logically isolated from each other.

Layer-3 network interconnection. Also known as data center frontend network interconnection, the so-called "frontend network" refers to the egress of the data center for enterprise campus network or enterprise wide area network. Frontend networks of different data centers (primary centers and disaster recovery centers) are interconnected through IP technology, and clients of the campus or branch access data centers through the frontend network. In the event of a disaster in the primary data center, the front-end network will quickly converge, and the client will access the disaster recovery center to ensure business continuity;

L2 network interconnection. Also known as the network interconnection of data center servers. Build a layer-2 network (VLAN) across data centers at the server network access layers of different data centers to meet the requirements for layer-2 network access in scenarios such as server clusters or dynamic migration of virtual machines;

SAN interconnection. Also known as backend storage network interconnection. With the help of Transmission Technology (DWDM, SDH, etc.), data is replicated between the master center and the disaster recovery center on the disk array.

Figure 1. Three interconnection modes of data centers

2. Business Requirements for layer-2 Data Center Interconnection

High-availability server cluster

A server Cluster is a logical server that uses Cluster software to associate multiple servers on the network to provide consistent services. Cluster software of most vendors (such as HP, IBM, Microsoft, and Veritas) requires layer-2 network interconnection between servers. Deploy servers in clusters in different data centers to achieve cross-Data Center application system disaster tolerance.

Server relocation and dynamic migration of virtual machines

During the expansion or relocation of a data center, physical servers must be migrated from one data center to another. In this process, the following two factors need to be taken into account to build a layer-2 interconnected network between data centers:

When the server is migrated to the new data center, if a L2 network is not built between the new and old centers, the server IP address of the new center is re-planned and DNS needs to be modified, or modify the Server IP address configured by the client application. Therefore, building a cross-center L2 network can retain the IP addresses of the migrated servers, thus simplifying the migration process;

During the server relocation period, only some servers in the server group can be migrated to the new center within a given period of time. To ensure business continuity, a cross-center server cluster needs to be established, build a cross-center L2 interconnected network to achieve smooth server migration.

Similar to server relocation, virtual machine migration is used ". Currently, some server virtualization software can dynamically migrate virtual machines between two virtualized physical servers (2 ). The VM migrated to another center not only retains the original IP address, but also maintains the running status before migration (such as the TCP session status ), therefore, physical servers involved in Virtual Machine migration must be connected to the same L2 network (the gateway of the virtual machine remains unchanged before and after migration). This application scenario requires building a cross-center L2 network.

Figure 2. dynamic migration of virtual machines