在juniper的设备中， routing instance是分很多种类的， 根据情况，需要进行配置的。
* Forwarding--Use this routing instance type for filter-based forwarding
applications. For this instance type, there is no one-to-one mapping
between an interface and a routing instance. All interfaces belong to
the default instance inet.0.
* Layer 2 VPN--Use this routing instance type for Layer 2 VPN
implementations.
* Layer2-control--Use this routing instance type for RSTP or MSTP in
customer edge interfaces of a VPLS routing instance. This instance
type cannot be used if the customer edge interface is multihomed to
two provider edge interfaces. If the customer edge interface is
multihomed to two provider edge interfaces, use the default BPDU
tunneling.
* Nonforwarding--Use this routing instance type when a separation of
routing table information is required. There is no corresponding
forwarding table. All routes are installed into the default forwarding
table. IS-IS instances are strictly nonforwarding instance types.
* Virtual router--This routing instance is similar to a VPN routing and
forwarding instance type, but used for non-VPN-related applications.
There are no VRF import, VRF export, VRF target, or route
distinguisher requirements for this instance type.
* Virtual switch--(MX-series routers only) Use the virtual switch
instance type to group one or more Layer 2 bridge domains. A bridge
domain consists of a set of ports that share the same flooding or
broadcast characteristics. Each virtual switch represents a Layer 2
network. You can optionally configure a virtual switch to support
Integrating Routing and Bridging (IRB), which facilitates simultaneous
Layer 2 bridging and Layer 3 IP routing on the same interface. You can
also configure Layer 2 control protocols to provide loop resolution.
Protocols supported include the Spanning Tree Protocol, the Rapid
Spanning Tree Protocol, and the Multiple Spanning Tree Protocol.
* VPLS--Use this routing instance type for point-to-multipoint LAN
implementations between a set of sites in a VPN.
* VRF--Use this routing instance type for Layer 3 VPN implementations.
For this instance type, there is a one-to-one mapping between an
interface and a routing instance. Each VRF instance corresponds with a
forwarding table. Routes on an interface go into the corresponding
forwarding table.
