Photo by Fikri Rasyid on Unsplash

Photo by Fikri Rasyid on Unsplash

Network overlay with VXLAN

Safety Net

Article from ADMIN 71/2022
VXLAN addresses the need for overlay networks within virtualized data centers accommodating multiple tenants.

If high availability or load balancing is required on servers across geographically separated locations, many of these services require direct access over Layer 2. However, if the Layer 2 link, which is based on classic 802.1Q VLAN technology, is interrupted by a routed link in Layer 3, the required transparency is lost. A virtual extensible local area network (VXLAN) solves this problem by extending Layer 2 accessibility over the existing Layer 3 structure with an overlay network.


System administrators face the challenge of planning scalable networks while maintaining appropriate security and availability requirements. Some server systems need to be located in a redundant infrastructure on a subnet. Additionally, virtualized systems need to be capable of migration between multiple sites on the same subnet, whether in live operation or in a disaster recovery scenario. Moreover, today's networks need be able to meet the increasing demand for bandwidth.

In classic scenarios, the required security can usually be achieved by implementing virtual local area networks (VLANs) to reduce the size of broadcast domains in combination with firewall rules or static packet filters (access control lists, ACLs) on routers or Layer 3 switches. In some cases, routing virtualization implemented by virtual routing and forwarding (VRF) is used at the routing level to enable multiclient capability.

Layer 2 Limitations

Routed networks are typically used to ensure scalability and avoid Layer 2 loops. Layer 2-only networks use methods such as Spanning Tree defined in IEEE 802.1d, its extension Rapid Spanning Tree (IEEE 802.1w), or Multiple Spanning Tree (IEEE 802.1s). All three have the advantage of ensuring loop-free operation. Layer 2 loops overload the switches and can be complex to troubleshoot.

Freedom from loops is ensured

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