A network engineer is implementing Layer 3 MPLS VPNs on Cisco IOS/IOS XE PE routers. Which PE- to-CE routing protocol requires a separate routing process to be created for each VRF?

On Cisco IOS and IOS XE platforms, when configuring OSPF as the PE-to-CE routing protocol in an MPLS Layer 3 VPN environment, a separate and unique OSPF process must be created for each VRF. The VRF is explicitly associated with the OSPF process at the time of creation using the router ospf vrf command. This design isolates the OSPF database, adjacencies, and routing information on a per-VRF basis by dedicating an entire routing process to it. In contrast, BGP, EIGRP, and RIPv2 utilize a single routing process and leverage the address-family configuration mode to support multiple VRFs, providing VRF-specific configuration within that single process.

A. RIPv2: RIPv2 uses the address-family ipv4 vrf sub-configuration mode within a single router rip process to support multiple VRFs.
C. BGP: BGP is configured for multiple VRFs using the address-family ipv4 vrf sub-configuration mode within a single router bgp process.
D. EIGRP: EIGRP uses the address-family ipv4 vrf sub-configuration mode within a single router eigrp process to manage different VRFs.

1. Cisco Systems, Inc., MPLS Layer 3 VPNs Configuration Guide, Cisco IOS XE Release 3S.

Section: "Configuring OSPF as the PE-to-CE Routing Protocol"

Content: This section explicitly states and demonstrates the required configuration: router ospf process-id vrf vrf-name. The guide notes, "A separate OSPF process is created for each VPN." This confirms that OSPF requires a distinct process per VRF.

Reference Link: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/mpl3vpns/configuration/xe-3s/mp-l3-vpns-xe-3s-book/mp-pe-ce-ospf.html

2. Cisco Systems, Inc., IP Routing: BGP Configuration Guide, Cisco IOS Release 15M&T.

Section: "MPLS VPN—BGP PE-CE"

Content: The configuration examples for BGP PE-CE routing show a single router bgp process with multiple address-family ipv4 vrf sections, demonstrating that a separate process is not required for each VRF.

Reference Link: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproutebgp/configuration/15-mt/irg-15-mt-book/irg-mpls-vpn-bgp-pe-ce.html

3. Cisco Systems, Inc., IP Routing: EIGRP Configuration Guide.

Section: "EIGRP VRF-Lite"

Content: This guide illustrates the use of address families for VRF support within a single EIGRP process (router eigrp ). The command structure address-family ipv4 vrf autonomous-system is used, confirming one process can handle multiple VRFs.

Reference Link: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iprouteeigrp/configuration/15-mt/ire-15-mt-book/ire-vrf-lite.html