1. A method for implementing a hierarchical Virtual Private LAN Service, comprising: using a Border Gateway Protocol in a Virtual Private LAN Service network; and implementing the hierarchical Virtual Private LAN Service in the Virtual Private LAN Service network using the Border Gateway Protocol, wherein: when a User-end Provider Edge router and a Service Provider-end Provider Edge router in the Virtual Private LAN Service network belong to different autonomous systems, a Border Gateway Protocol connection is used between the User-end Provider Edge router and the Service Provider-end Provider Edge router, and among the Service Provider-end Provider Edge routers; and implementing the hierarchical Virtual Private LAN Service in the Virtual Private LAN Service network using the Border Gateway Protocol comprises: setting a Split-Horizon Disable Flag in a Border Gateway Protocol neighbor in a Border Gateway Protocol Virtual Private LAN Service address family, when all the Virtual Private LAN Service network hierarchies between the User-end Provider Edge router and the Service Provider-end Provider Edge router are consistent; and implementing the hierarchical Virtual Private LAN Service in the Virtual Private LAN Service network according to the Split-Horizon Disable Flag.