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352-001 · Question #624

A service provider must provide Internet connectivity to an MPLS Layer 3 VPN customer. Which solution allows this customer to have Internet access?

The correct answer is C. Implement a default route in the VRF with a next hop in the global routing table of PE. Providing Internet access to an MPLS L3 VPN customer requires leaking a default route from the VRF to the global routing table on the PE router using a globally-scoped next hop.

Designing Network Services

Question

A service provider must provide Internet connectivity to an MPLS Layer 3 VPN customer. Which solution allows this customer to have Internet access?

Options

  • AImplement a global default route with a next hop in the VRF late on PE
  • BImplement policy-based routing between PE and CE
  • CImplement a default route in the VRF with a next hop in the global routing table of PE
  • DImplement destination NAT between the VRF and the global RIB of PE

How the community answered

(30 responses)
  • A
    13% (4)
  • B
    7% (2)
  • C
    77% (23)
  • D
    3% (1)

Why each option

Providing Internet access to an MPLS L3 VPN customer requires leaking a default route from the VRF to the global routing table on the PE router using a globally-scoped next hop.

AImplement a global default route with a next hop in the VRF late on PE

A global routing table default route cannot have its next hop resolved inside a VRF; route leaking between tables is directional and must be initiated from within the VRF.

BImplement policy-based routing between PE and CE

Policy-based routing between PE and CE can redirect traffic based on match criteria but does not bridge the routing table separation between a VRF and the global table.

CImplement a default route in the VRF with a next hop in the global routing table of PECorrect

A static default route is configured inside the customer VRF pointing its next hop to an interface or address in the PE's global routing table using the 'global' keyword (e.g., 'ip route vrf <name> 0.0.0.0 0.0.0.0 <next-hop> global'). This VRF-to-global route leaking enables the customer's Internet-bound traffic to exit the isolated VRF context and be forwarded through the PE's global Internet routing table. This is the standard and supported method for shared Internet access in MPLS VPN deployments.

DImplement destination NAT between the VRF and the global RIB of PE

Destination NAT translates inbound destination addresses and does not address the routing plane separation between a VRF and the global RIB needed for outbound Internet access.

Concept tested: MPLS L3 VPN Internet access via VRF route leaking

Source: https://www.cisco.com/c/en/us/support/docs/multiprotocol-label-switching-mpls/mpls/13718-mpls-vpn-internet.html

Topics

#MPLS L3 VPN#VRF#Internet access#default route

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