The core routers do not care about the customers' IP packet for forwarding, but see a labeled packet targeted toward an egress PE router. So, in the most common form, two labels are added to customer traffic. The transit across the backbone is performed by using the labels that had been exchanged for routes in the global IP routing table. The core routers in the provider network (P routers) that provide transport across the provider's backbone are not aware of customer routes. While the VRF tables provide the isolation between customers, the data from these routing tables is exchanged between PE routers to enable data transfer between sites attached to different PE routers. The PE routers maintain a separate routing table for each customer VPN called a virtual routing and forwarding (VRF) table. If site Routers CE1 and CE3 belong to the same customer and VPN, their traffic is segmented from other customers' traffic and marked with a label. MPLS VPN uses a shared infrastructure but provides security for customers' traffic. Part of the customer network that interfaces with the PE Part of the provider network that interfaces with the CE router and P and PE routers Part of provider network that interfaces with PE and other P routers This chapter discusses some of these issues across various Cisco platforms. Sometimes administrators believe the issue is with CEF, but it is with routing design. Although issues can occur with MPLS VPN setup, label distribution protocol (LDP), and operation, many times the issues relate to label mismatches stored in CEF or some other CEF inconsistency. This chapter assumes a basic understanding of MPLS VPNs. Therefore, MPLS VPN relies on CEF because MPLS VPN depends on MPLS for successful operation. MPLS forwarding relies heavily on the IP routing table and the CEF architecture. Without CEF, MPLS forwarding does not occur. Because of increased MPLS VPN usage, you need to understand CEF's role, especially when troubleshooting.ĬEF is the fundamental switching path for MPLS. They also deploy MPLS VPNs for reasons including scalability, security, and flexibility. Service providers and enterprises are increasingly using MPLS to provide connection-oriented services using an IP infrastructure. This chapter analyzes CEF in MPLS Virtual Private Network (VPN) applications across Cisco platforms. Understanding CEF operation in a Multiprotocol Label Switching (MPLS) environment is important for design stability and troubleshooting.
Understanding the CEF and MPLS relationshipĬEF considerations when troubleshooting MPLS VPN across various platformsĬEF and MPLS VPN load-sharing considerations An Internet service provider's simple MPLS VPN design