Which is the primary function of a MPLS L3 VPN route target?

Question

Options

• AIt imports and exports identified routes into selected VRFs.
• BIt uniquely identifies NLRIs that have the same numeric value.
• CIt imports the external routes it identifies into VRFs that support Internet traffic
• DIt supports QoS by classifying traffic by file type when it applies MPLS EXP bits to each packet.

• A
  91% (39)
• B
  2% (1)
• C
  5% (2)
• D
  2% (1)

Explanation

A Route Target (RT) is a BGP extended community attribute that controls which routes get imported into (and exported from) VRF routing tables in an MPLS L3 VPN - making A correct. When a PE router exports a VPN route, it tags it with an export RT; other PE routers import that route only if it matches an RT in their VRF's import policy, giving service providers precise control over which sites share routing information.

Why the distractors are wrong:

• B describes the Route Distinguisher (RD), not the RT. The RD makes overlapping customer prefixes globally unique in the BGP table but plays no role in route import/export decisions.
• C is a partial truth twisted into a trap - RTs can be configured to leak internet routes into VRFs, but the primary function is general VRF route import/export control, not an internet-traffic-specific role.
• D is unrelated entirely; MPLS EXP (now called TC) bits handle QoS/traffic classification at the label level, a completely separate mechanism from route targets.

Memory tip: Think of a Route Target as a mailing label - the export RT stamps it on the envelope, and the import RT is the address filter that decides which VRF "mailbox" accepts it. RD = unique sender ID; RT = delivery rule.

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