The concept of Virtual Routing and Forwarding (VRF) is similar to the virtual router (VR) already present in Extreme Switches. Like a VR, each VRF also has a distinct set of VLANs and ports, as well as a unique name assigned to it across the system. VLANs are created, and ports are added to in the same manner as is done for VRs. Logically separate instances of the same routing protocol may run in the contexts of multiple VRFs of the same switch, simultaneously. In addition, a VRF may also contain a Route Distinguisher (RD), multiple import and export Router Targets (RTs), as well as a VPN ID. These three items allow a VRF to support L3VPNs.
The goal of VRF is to provide separation of overlapping address spaces belonging to separate routing domains. The objective of the VR is to split the switch into multiple routing domains so that traffic originating on one VR never enters another VR. The objective of VRFs is to control the flow of traffic across various VPN sites. As the PE-PE connection is always part of the default VR or a user VR, the forwarding table corresponding to a particular VRF has the incoming interface belonging to the VRF, and egress interfaces belonging to the default, or user VR. Similarly, the forwarding table (MPLS (Multiprotocol Label Switching) label table) corresponding to a user, or default VR, could have an interface belonging to a VRF as part of its egress interfaces. In this sense a VRF is "associated" with the user, or default VR (also refered to as parent VRs).
A VRF is not the same as a VR. A VRF always requires that you have a Parent VR, and this can either be the default VR or User VR. Protocols running in a VRF run as a separate logical instance within the context of the protocol process that is running in the Parent VR. EXOS VRFs come in two types:
Note
MPLS and BGP must be configured in the parent VR (PE-facing).Again, a VRF always requires that you have a Parent VR, and this can either be the default VR or User VR. Protocols running in a VRF run as a separate logical instance within the context of the protocol process that is running in the Parent VR. For example, the BGP process for a VR running MPLS will handle all PE to CE instances of BGP by virtualizing the data structures. This approach of allowing VRFs in a VR is more scalable than having a process for every instance of PE-to-CE routing protocol.
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