In MPLS Layer 3 VPN implementations, which mechanism is used to control which routes are imported to a VRF?

Question

Options

• ART
• BRD
• CVC ID
• DPW ID
• EVRF ID

• A
  90% (37)
• B
  5% (2)
• C
  2% (1)
• D
  2% (1)

Explanation

Route Targets (RT) are BGP extended communities attached to VPNv4 routes that act as import/export filters - when a route is exported from a VRF it receives an RT tag, and a receiving VRF only imports routes whose RT matches its configured import policy, giving administrators fine-grained control over which sites share routing information.

RD (Route Distinguisher) is a 64-bit prefix prepended to IPv4 routes to make them globally unique in the BGP table, but it plays no role in import filtering - it only prevents address-space collisions. VC ID and PW ID belong to Layer 2 VPN technologies (like VPLS or pseudowires), not L3 VPN route control. VRF ID is a local router concept for identifying a VRF instance; it has no significance in inter-PE route exchange.

Memory tip: Think of RT as a "routing ticket" - a route must carry the right ticket to get into a VRF, while RD is just the route's unique "name tag" so no two routes look identical in the global table.

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