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CCNP Service Provider study materials
CCNP Service Provider study resources

CCNP Service Provider: Service Provider Routing and Switching

CCNP Service Provider · Work through your exam, one topic at a time.

All guide sections

Service Provider Routing and Switching

Domain 2 (25%) covers the IGPs and BGP that carry SP routes plus the Layer 2 switching used in access and aggregation. Expect best-path questions, policy, route reflection, and L2 redundancy.

IGP selection and tuning

  • IS-IS is common in the core: L1/L2, wide metrics, TLV extensibility, and independence from IP addressing.
  • OSPFv2/v3 appears at edge and enterprise handoffs: areas, LSA types, stub/NSSA, virtual links; OSPFv3 uses link-local addressing.
  • Use passive interfaces, authentication (HMAC-MD5/SHA), and metric tuning to steer traffic.

BGP fundamentals and policy

  • eBGP sets the next hop to self; iBGP preserves it, so edge and RR routers often need next-hop-self.
  • iBGP split horizon requires a full mesh, route reflectors, or confederations.
  • Cisco best-path order: weight, local preference, locally originated, AS path length, origin, MED, eBGP over iBGP, IGP metric to next hop, oldest route, lowest router ID, shortest cluster list, lowest neighbor address.
  • Communities (standard, extended, large) tag routes; route-maps and prefix-lists implement policy.
  • Route reflection uses cluster ID and originator ID for loop prevention. BGP PIC precomputes backup paths; BGP-LS exports topology.

Layer 2 switching

  • 802.1Q trunks, native VLAN, QinQ (802.1ad) for transparent customer VLANs.
  • STP/RSTP/MST, REP, G.8032 ERPS, and private VLANs provide loop-free or isolated L2 services.

Worked example

A route to 198.51.100.0/24 is learned from peer A with weight 200 and from peer B with local preference 300. Both are eBGP with equal AS path length and origin. Which wins? Weight is compared first, so peer A is selected despite the lower local preference. Weight is Cisco-proprietary and local to the router; local preference is AS-wide but comes later in the decision process. Only when weights tie does local preference matter.

Traps

  • Reversing weight and local preference.
  • Comparing MED from different neighboring ASes; MED is not propagated beyond the neighbor AS.
  • Forgetting next-hop-self on an RR or edge router.
  • Expecting an RR to reflect a route back to its originator; originator ID and cluster list prevent it.
  • Mismatched MST region parameters.
  • Assuming OSPF DR election is based on highest IP rather than priority and Router ID.