Refer to the exhibit. This is an MPLS VPN network with OSPF as the PE-CE routing protocol. Which statement is correct?

Question

Exhibit

Options

• AThe routing inside the VPN RED will never work correctly.
• BThe routing inside the VPN RED can be enabled by configuring virtual links between the PE
• CThe routing inside the VPN RED can be enabled by configuring area 0 inside the VRF on the
• DThe routing inside the VPN RED will work without any special OSPF configuration.
• EThe routing inside the VPN RED will work if the PE routers have a full mesh of sham-links

• A
  6% (2)
• B
  15% (5)
• C
  6% (2)
• D
  71% (24)
• E
  3% (1)

Explanation

In MPLS VPN environments using OSPF as the PE-CE routing protocol, Cisco IOS implements a 'super backbone' mechanism. The PE routers act as OSPF ABRs, and the MPLS/BGP core emulates an OSPF Area 0 backbone between them. OSPF routes are carried across the VPN backbone in BGP using special extended communities (domain-ID, OSPF route-type, MED) that preserve OSPF attributes. When routes arrive at the remote PE, they are re-injected into OSPF with correct LSA types, making the routing transparent to CE routers. This works automatically without requiring sham-links (which are only needed to prefer the MPLS path over a backdoor OSPF link) or manual virtual links.

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