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352-001 · Question #31

Refer to the exhibit. Your junior design engineer presents this configuration design. What is the next-hop router for CE3, and why?

The correct answer is A. CE1. BGP weight is higher than CE2.. BGP Weight is a Cisco-proprietary, locally significant attribute evaluated first in path selection; a higher weight on the CE1 path means CE3 will prefer CE1 as its next hop.

Layer 3 Control Plane

Question

Refer to the exhibit. Your junior design engineer presents this configuration design. What is the next-hop router for CE3, and why?

Exhibit

352-001 question #31 exhibit

Options

  • ACE1. BGP weight is higher than CE2.
  • BCE2. EBGP administrative distance is lower than RIP.
  • CCE2. The link between CE2 and PE1 has more bandwidth than CE1-to-PE1.
  • DCE1. HSRP on CE1 is in active state.

How the community answered

(60 responses)
  • A
    78% (47)
  • B
    13% (8)
  • C
    3% (2)
  • D
    5% (3)

Why each option

BGP Weight is a Cisco-proprietary, locally significant attribute evaluated first in path selection; a higher weight on the CE1 path means CE3 will prefer CE1 as its next hop.

ACE1. BGP weight is higher than CE2.Correct

BGP path selection evaluates Weight first - the path with the highest Weight value is always preferred above all other attributes. Because CE1 has a higher BGP Weight than CE2, CE3 will select CE1 as its next hop regardless of other factors such as administrative distance or bandwidth. Weight is locally significant to the router performing the selection and is never advertised to BGP peers.

BCE2. EBGP administrative distance is lower than RIP.

Administrative distance is used to choose between routes learned from different routing protocols, not between multiple BGP paths on the same router; BGP Weight takes precedence in the BGP best-path selection process before administrative distance is relevant.

CCE2. The link between CE2 and PE1 has more bandwidth than CE1-to-PE1.

Interface bandwidth is not a factor in the BGP best-path selection algorithm; BGP does not consider link bandwidth when choosing between candidate paths.

DCE1. HSRP on CE1 is in active state.

HSRP active/standby state determines the default gateway for locally attached hosts using a virtual IP address, and has no influence on BGP next-hop selection for CE3.

Concept tested: BGP Weight attribute in path selection

Source: https://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/13753-25.html

Topics

#BGP weight#administrative distance#CE router#path selection

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