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400-007 · Question #53

A senior network designer suggests that you should improve network convergence times by reducing BGP timers between your CE router and the PE router of the service provider. Which two factors should…

The correct answer is A. service provider agreement to support tuned timers D. number of routes on the CE router. Tuning BGP timers between a CE and PE router requires the service provider's cooperation and an understanding of the CE router's route processing capacity.

Designing Network Infrastructure

Question

A senior network designer suggests that you should improve network convergence times by reducing BGP timers between your CE router and the PE router of the service provider. Which two factors should you consider to adjust the timer values? (Choose two.)

Options

  • Aservice provider agreement to support tuned timers
  • Bmanual updates to the peer groups
  • Cservice provider scheduling of changes to the PE
  • Dnumber of routes on the CE router
  • Enumber of VRFs on the PE router

How the community answered

(51 responses)
  • A
    73% (37)
  • B
    10% (5)
  • C
    14% (7)
  • E
    4% (2)

Why each option

Tuning BGP timers between a CE and PE router requires the service provider's cooperation and an understanding of the CE router's route processing capacity.

Aservice provider agreement to support tuned timersCorrect

The PE router is owned and managed by the service provider, so any timer changes on the PE side require a formal agreement or change request, as the SP must configure matching timers for the BGP session to remain stable.

Bmanual updates to the peer groups

Peer groups are an administrative tool for applying consistent configuration to multiple neighbors and do not need manual updates simply because timers are being tuned.

Cservice provider scheduling of changes to the PE

The service provider's change scheduling is an operational process consideration, not a technical design factor that determines what timer values are appropriate.

Dnumber of routes on the CE routerCorrect

A larger routing table on the CE router increases CPU processing time for BGP updates; if timers are set too low without accounting for this load, the router may fail to send keepalives in time, causing unintended BGP session drops.

Enumber of VRFs on the PE router

The number of VRFs on the PE affects overall PE resource consumption but does not directly determine the appropriate BGP keepalive or hold-time values for a specific CE-PE session.

Concept tested: BGP timer tuning factors for CE-PE adjacency

Source: https://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/213702-understand-bgp-timers.html

Topics

#BGP timers#CE-PE design#convergence tuning#service provider agreement

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