4A0-106 practice question 17 of 30

An advantage of using BGP as the PE-CE protocol is that route policies are no longer required to control the exchange of routes from BGP to MP-BGP.

Full set: 214 questions
Answer options
A: True
B: False
Correct Answer:
FALSE
Explanation

The statement is false. Route policies are a fundamental and mandatory component for controlling the exchange of routes between a customer's VRF (VPN Routing and Forwarding) instance and the provider's MP-BGP backbone. When BGP is used as the PE-CE protocol, the PE router learns standard IPv4 routes from the CE. An export policy must be applied on the PE to select which of these learned routes are redistributed into MP-BGP, converted into VPN-IPv4 prefixes, and advertised to other PE routers. This policy mechanism is critical for security, preventing route leaks, and applying specific attributes (like site-of-origin or other communities) to customer routes as they traverse the provider's core network. The use of BGP as the PE-CE protocol does not eliminate this requirement; in fact, it often necessitates more sophisticated policies to leverage BGP's rich attribute set.

Why Incorrect

The statement "True" is incorrect because it posits that using BGP as the PE-CE protocol obviates the need for route policies to control redistribution into MP-BGP. This is fundamentally wrong. The process of taking routes from a specific customer's routing domain and advertising them into a shared backbone always requires a policy control point to ensure proper route filtering and attribute manipulation, regardless of the PE-CE protocol in use.

References

1. Nokia 7750 SR OS Services Guide, Release 22.10.R1, Chapter: Virtual Private Routed Network Services, Section: VPRN BGP. The documentation explicitly describes the configuration process where export policies are applied to the VPRN BGP instance. It states, "Export policies are used for routes advertised to other BGP peers." This includes the MP-BGP peers in the core, confirming that policies are used to control the redistribution from the VRF's BGP table into the core MP-BGP advertisements. The configuration context config>service>vprn>bgp>export is the mechanism for applying this control.

2. RFC 4364 - BGP/MPLS IP Virtual Private Networks (VPNs), Section 4.3.2, "Exporting VPN-IPv4 Routes from VRFs to BGP." This foundational RFC directly addresses the process. It states: "The PE's decision to export a particular route from a particular VRF is a matter of policy." This confirms that a policy-based decision is an integral part of the architecture for deciding which routes learned from a CE are advertised to other PEs.

3. Nokia Data Center Fabric with SR Linux Cookbook, Section 3.3.2.2, "EVPN-VXLAN L3 service for inter-subnet forwarding." While discussing a different encapsulation (EVPN-VXLAN), the principle remains identical for L3VPN services. The guide shows the application of an export policy (from-ip-vrf-1) to the BGP instance within the VRF to control which routes are advertised into the EVPN fabric. This demonstrates the consistent requirement for export policies in Nokia's L3VPN service architecture. The configuration snippet shows: bgp { export-policy from-ip-vrf-1; } within the VRF context, reinforcing the necessity of policy control.

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