In a typical service provider environment, which two tools are used to help scale PE router connectivity requirements? (Choose two.)

Question

Options

• Aroute reflectors
• BVPNv4 address family
• Coriginator ID
• Dcluster ID
• Econfederations

• A
  76% (22)
• B
  3% (1)
• C
  7% (2)
• D
  14% (4)

Explanation

Route reflectors (A) and confederations (E) both solve the same fundamental iBGP scaling problem: without them, every PE router must maintain a full mesh of iBGP sessions with every other PE router, which grows at O(n²) and quickly becomes unmanageable in large provider networks. Route reflectors designate a central hub that redistributes routes on behalf of clients, collapsing the full mesh into a hub-and-spoke model. Confederations split a single AS into smaller sub-ASes, allowing eBGP-like peering between sub-ASes and drastically reducing intra-AS full-mesh requirements.

The distractors are wrong because they are attributes used within these mechanisms, not scaling tools themselves: originator ID (C) and cluster ID (D) are BGP path attributes that route reflectors use internally to prevent loops - they're byproducts of route reflection, not independent solutions. VPNv4 address family (B) is the MP-BGP address family that carries labeled VPN routes, which is necessary for MPLS L3VPN operation but does nothing to reduce the number of BGP peering sessions.

Memory tip: Think of A and E as the two "session reducers" - Route reflectors Reduce sessions via a hub, confederations Chop the AS into pieces. Everything else (originator ID, cluster ID, VPNv4) is plumbing inside those mechanisms, not the mechanisms themselves.

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