Virtual border routers (VBRs) are virtualization of physical connection ports that are isolated by Alibaba Cloud. VBRs are defined on top of the Layer 3 overlay and switch virtualization technologies in the Software Defined Network (SDN) architecture. A VBR functions as a router between a customer-premises device and a virtual private cloud (VPC). VBRs route traffic between VPCs and data centers.
Each VBR is associated with a route table, which is similar to the vRouter of a VPC. You can add routes to the route table of a VBR to control traffic forwarding on the VBR.
VBRs provide the following features:
- Exchange data between a VPC and a data center.
- Add or identify VLAN tags in Layer 3 subinterface mode.
- Determine the mode of a physical connection port: Layer 3 router interface or VLAN Layer 3 subinterface.
- Support Border Gateway Protocol (BGP).
BGP is a dynamic routing protocol based on Transmission Control Protocol (TCP). BGP is used to exchange routing information and network accessibility information among autonomous systems. When you create physical connections to connect a data center to a VBR, you can configure BGP settings. BGP helps you build hybrid clouds in a more efficient, flexible, and reliable way.
- Source address-specific policy-based routes are not supported.
- Each VBR can be associated with only one route table.
- VBRs support only BGP4.
- VBRs support IPv4 BGP. IPv6 BGP is not supported.
- You can create up to eight BGP peers for each VBR.
- Each BGP peer supports up to 100 dynamic routes. If the number of dynamic routes that a BGP peer learns reaches the upper limit, the system generates an alert. However, the dynamic routes are not denied.
- To configure BGP when you connect to a VPC, you must specify an Autonomous System Number (ASN) for the VPC. The ASN that you specify must not be the same as the ASNs of the vSwitches in the VPC.