VXLAN OVERLAY NETWORK
VXLAN overlay networks can be classified into network overlay, host overlay, and hybrid overlay based on the device models functioning as VTEPs.
- • Network overlay: All VTEPs are deployed on physical switches.
- • Host overlay: All VTEPs are deployed on vSwitches.
- • Hybrid overlay: Some VTEPs are deployed on physical switches with others deployed on vSwitches.
VXLAN Overlay Network Types
1. Network overlay
Network overlay is classified into centralized and distributed network overlay. The VTEPs of a VXLAN tunnel are physical switches, as shown in Figure 6.4.
• Centralized network overlay: Leaf nodes act as Layer 2 VXLAN gateways, with spine nodes or border leaf nodes acting as Layer 3 VXLAN gateways.
FIGURE 6.4 Centralized and distributed network overlay.
- • Distributed network overlay: Leaf nodes function as Layer 2 and Layer 3 VXLAN gateways. Spine nodes are restricted to forwarding IP packets at a high speed and do not process VXLAN packets.
- 2. Host overlay
All VTEPs are vSwitches deployed on servers, as illustrated in Figure 6.5. East-west traffic in a DC is forwarded between vSwitches through a VXLAN tunnel, and north-south traffic is forwarded between vSwitches and vRouters. Physical switches that function as leaf and spine nodes are only able to forward IP packets at high speed and additionally do not process VXLAN packets.
3. Hybrid overlay
VTEPs can be vSwitches or physical switches, as shown in Figure 6.6, with distributed mode frequently used.
FIGURE 6.5 Host overlay.
FIGURE 6.6 Hybrid overlay.
East-west traffic in a DC is forwarded through VXLAN tunnels between vSwitches and physical switches (leaf nodes). North-south traffic is forwarded through VXLAN tunnels between vSwitches or physical switches (leaf nodes) and spine nodes or border leaf nodes.
Comparison of VXLAN Overlay Network Types
In the preceding three VXLAN overlay network types, the network overlay is recommended for the cloud DCN solution. Comparison of the host overlay and hybrid overlay is recommended in only limited scenarios.
The advantage of the network overlay, in contrast to the host overlay and hybrid overlay, is that physical switches are able to function as VTEPs. VXLAN path calculation is performed on switches, exhibiting forwarding performance, O&M convenience, and security advantages over software switches. Additionally, in terms of interconnection between SDN and traditional networks, interconnection between physical switches and traditional networks is more convenient than interconnection between software switches and traditional networks.
Table 6.1 compares the three overlay network types.
For centralized and distributed network overlay, distributed network overlay is advantageous. In the centralized network overlay scenario, all traffic across network segments has to be forwarded through the centralized gateway, imposing substantial pressure on the centralized gateway. Therefore, the number of services supported in the centralized network overlay scenario is limited, meaning poor network scalability.
In the majority of scenarios, the distributed network overlay solution is recommended as the preferred DCN deployment solution. Table 6.2 compares the centralized and distributed network overlay.