# Overview

#### User-defined Network

BMSs support secondary virtualization. The user-defined network enables communication between the VM network and the VPC, and provides functions similar to the VPC network for VMs. Application scenarios and benefits include:

- Private clouds such as XenServer, VMware, and Hyper-V can be provisioned using BMSs.
- VMs or containers provisioned in the private cloud on BMSs can communicate with the Internet.
- VMs or containers provisioned in the private cloud on BMSs can communicate with each other.
- Network ACLs can be configured for the subnets of the VMs or containers provisioned in the private cloud on BMSs.
- VMs or containers provisioned in the private cloud on BMSs can communicate with ECSs in VPCs.
- The private cloud system based on BMSs and Direct Connect can communicate with the private cloud in the on-premise data center.

#### Notes

- If you have multiple VPCs, you can only create user-defined networks in one VPC.
- If each of your BMSs has only one NIC, you cannot create user-defined networks.
- You must create a BMS with a user-defined VLAN before creating a user-defined network.
- A maximum of two user-defined networks can be created.
- Security groups cannot be configured for user-defined subnets.

Parent topic: User-defined Network