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JNCIE-SP study materials
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JNCIE-SP: BGP and Service Provider Routing

JNCIE-SP · Work through your exam, one topic at a time.

All guide sections

BGP and Service Provider Routing

What this domain tests

BGP questions cover iBGP scaling, route reflection, confederations, attribute manipulation, best-path selection, and interaction with the IGP. The exam expects you to know which attributes are transitive and where policy is applied.

Core rules

  • iBGP has split horizon: a route learned from an iBGP peer is not sent to another iBGP peer. Fix with a full mesh, route reflector, or confederation.
  • A route reflector needs cluster <id> and clients; the cluster list prevents loops. The RR does not change next hop by default; next-hop-self is a separate policy decision.
  • Confederations use set routing-options confederation <as> members [...] and a confederation identifier; confederation AS_PATH segments are removed at the border.
  • Best path in Junos starts with weight, then local preference, locally originated, shortest AS path, origin, MED, eBGP over iBGP, lowest IGP metric, oldest route, lowest router ID, shortest cluster list, and lowest peer address.
  • MED is compared only among paths from the same neighbor AS unless always-compare-med is configured. Local preference is not sent to eBGP peers.
  • BGP next hop must resolve in inet.0; show route protocol bgp hidden shows unresolved or rejected routes.

Worked example

Two PEs peer with a route reflector:

set protocols bgp group RR type internal local-address 10.0.0.1
set protocols bgp group RR cluster 10.0.0.1
set protocols bgp group RR family inet unicast
set protocols bgp group RR neighbor 10.0.0.2

Reasoning: PE2 sends its routes to the RR; the RR reflects them to other clients and adds the cluster ID. Without the cluster ID, a reflected route could loop back. If the RR is also a transit router, apply next-hop-self on its edge policy so clients can resolve the next hop.

Traps

  • A route reflector does not automatically set next-hop-self.
  • local-preference is iBGP-only in practice and is stripped at eBGP boundaries.
  • MED comparison across different neighbor ASes requires explicit configuration.
  • A BGP route can be valid but hidden because its next hop is unresolved; check the IGP route, not just BGP.