When 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?

Question

Options

• AEIGRP
• BRIPv2
• COSPF
• DBGP

• A
  6% (3)
• B
  2% (1)
• C
  90% (47)
• D
  2% (1)

Explanation

OSPF is the correct answer because Cisco IOS/IOS XE requires a separate OSPF process per VRF - each router ospf <process-id> vrf <name> instantiation is distinct, so a PE with 50 VRFs needs 50 OSPF processes, which creates scalability concerns unique to OSPF in L3 VPN deployments.

Why the distractors are wrong:

• A (EIGRP): EIGRP uses address-family configuration under a single process (router eigrp <ASN> → address-family ipv4 vrf <name>), so one process handles all VRFs.
• B (RIPv2): RIPv2 also supports per-VRF address families under a single router rip process, similar to EIGRP.
• D (BGP): BGP is typically the PE-to-PE protocol (MP-BGP), but when used as PE-to-CE it also leverages address families under one router bgp <ASN> process.

Memory tip: Think "OSPF = One Separate Process per VRF" - the acronym OSPF itself reminds you it needs its own process for each VRF, unlike EIGRP and RIP which use the address-family model under a single process.

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