The Network Extension Service extends a Layer 2 network from the on-premises vSphere data center to vCloud Air.

The Layer 2 Concentrator virtual service appliances make extension possible. The Layer 2 Concentrators have two interfaces:

Internal trunk interface: Handles virtual machine traffic on-premises for the extended networks using a translational bridge mapping to a corresponding stretched network in vCloud Air.

Uplink interface: Hybrid Cloud Manager uses this interface to send encapsulated overlay traffic to and from vCloud Air. Application data travels through this interface.

As shown in Comparing Layer 2 Concentrators, the two concentrators are based on different technology. The newer high-throughput L2C is a much larger appliance, as described in Virtual Machine Resource Requirements.

Comparing Layer 2 Concentrators

Feature

Standard L2C

HT L2C

Transport

TCP/SSL, Internet, or Direct Connect

IP SEC, Direct Connect

IP Address

Can use default non-routable IP in a fleet deployment, or a routable IP address

Requires routed management IP address in all deployments.

NAT rules

Yes

Yes

Proximity routing

Yes

Yes

Jumbo frame support

No

Yes

Max connections per vLAN

Many

One

Layer 2 Appliance Position in the Single-Path Deployment

The configuration wizard's default strategy is to define the Cloud Gateway, then place the Layer 2 Concentrator "behind" the Cloud Gateway. The WAN optimizer bootstraps from the Cloud Gateway so it uses the gateway’s address by default, as shown in Figure 1.

If the appliance is a standard L2C, this "single-path" strategy routes all traffic through the Cloud Gateway and uses only one IP address. Internally, the Layer 2 Concentrator is assigned a non-routable IP address, so the IP address assigned to the Cloud Gateway is the only one consumed.

If you are using an HT L2C, you must assign a routable IP address, therefore two IP addresses are consumed.

Layer 2 Appliance Position for an Alternate Path

If you have a single-path deployment you can add multiple "standalone" appliances, where an L2C with a unique IP address forms a separate edge. Standalone appliances can be used to route vLANs through the cloud gateway, to extend a network to vCloud Air, or to carry communication between virtual machines.

If you use an HT L2C to extend a network, each vLAN can have only one HT L2C connection. A Direct Connect private line is a typical.

The standard L2C permits multiple connections, for scaling out a deployment. See Network Extension.