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Use Case Overview


Need For a Layer 2 Overlay

In traditional data centers, Layer 2 technologies are often used to support various design requirements, including:

  • Heartbeat exchange and internode communication between high availability clusters

  • Server farm growth and physical server placement flexibility

  • Virtual machine (VM) migration

  • Disaster recovery and geographically dispersed clustering

The Juniper Networks Virtual Chassis Fabric (VCF) provides a low-latency, high-performance Layer 2 fabric architecture for data centers that can be managed as a single device, and meets the requirements of many data center environments.

However, as the design of these data centers evolves to scale out multitenant networks, a new data center architecture is needed that decouples the underlay (physical) network from a tenant overlay network. Using a Layer 3, IP-based underlay coupled with a Virtual Extensible LAN (VXLAN)-Ethernet VPN (EVPN) overlay, data center and cloud operators can deploy much larger networks than are otherwise possible with traditional Layer 2, Ethernet-based architectures. With overlays, endpoints (servers or VMs) can be placed anywhere in the network and remain connected to the same logical Layer 2 network, enabling the virtual topology to be decoupled from the physical topology.

Virtual Chassis Fabric Integration with IP Fabric Architectures

Starting with Junos OS Release 14.1X53-D40, a VCF can integrate with EVPN-VXLAN environments and act as an EVPN PE device. This enables the entire VCF–with up to 16 top-of-rack (TOR) switches–to appear as a single PE device, with a single VXLAN tunnel endpoint (VTEP). This capability maintains the existing Ethernet fabric for intra-VCF traffic, with all the advantages and features it provides, while also merging it with the larger EVPN-VXLAN IP fabric to provide connectivity with the rest of the data center.


Server multihoming to redundant TOR devices is another common requirement in data centers. Traditionally, this requirement required proprietary solutions such as multichassis link aggregation (MC-LAG) or Virtual Chassis/VCF. While each solution has its merits, it does require the same vendor across these devices, and in the case of MC-LAG, multihoming is limited to two PE devices.

Ethernet VPN (EVPN), on the other hand, is a standards-based multihoming solution that can scale horizontally across any number of PE devices, and seamlessly integrates into multivendor Layer 3 IP fabrics. With support for active-active endpont mulithoming, EVPN can enable redundant server connections to multiple VCFs to provide fabric level redundancy.