DCI Deployment Solution

Layer 2 interconnection

As shown in Figure 2-5, configure the DCI leaf nodes to communicate with each other at Layer 3 and establish a VXLAN tunnel. Set up M-LAGs for DCI leaf nodes and local spine nodes separately and implement multi-level M-LAG interconnection.

After traffic on the spine nodes is forwarded to the DCI leaf nodes, VLAN IDs are mapped to the BDs of the VXLAN network. Then the traffic is forwarded to the peer DCI leaf nodes at Layer 2 for decapsulation and BDs are restored to VLAN IDs on the destination network.

Layer 3 interconnection

Configure Layer 3 interfaces on the DCI leaf nodes to directly connect to the local spine nodes. On the spine nodes, configure static routes to the local DCI leaf nodes to reach the peer DC.

On the DCI leaf nodes, configure static routes to the local spine nodes and import the routes to the BGP EVPN routing table.

The traffic on the spine nodes is forwarded to the DCI leaf nodes based on the configured static routes. Then the traffic is forwarded to the peer DCI leaf nodes based on the IBGP EVPN routing table, and then the spine nodes in the backup DC based on static routes.

Directly connecting spine nodes in different DCs in multi-level M-LAG interconnection mode

• STP should be deployed for Layer 2 interconnection to prevent loops. However, you are not advised to implement Layer 2 interconnection between DCs. If two DC-level networks interconnect using STP, the STP network computing domain is large, and the convergence is slow. The fault domain of STP convergence is large, and faults on one DC-level network will affect the other network.
• In each DC, active-active gateways are deployed on the spine nodes and function as STP root nodes. However, only one STP root node can be deployed on an STP network. If not, the change of one root node will incur STP flapping in the other DCs.
• The direct Layer 2 interconnection solution can involve only two DCs, and the network scalability is limited. (More DCs may cause loops.)

Connecting M-LAGs of DCI leaf nodes in different DCs

Combing DCI leaf nodes and spine nodes and deploying VXLAN

• Poor scalability: The configuration is complex when multiple fabrics in a DC need to communicate with the backup DC.
• Low compatibility: In Layer 2 interconnection scenarios, traditional VLANIF interfaces cannot function as VXLAN gateways. Therefore, the configuration for service gateways in a DC needs to be changed to enable VXLAN gateways.