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300-415 · Question #86

300-415 Question #86: Real Exam Question with Answer & Explanation

The correct answer is B: configure "Overlay AS Number". Configuring the Overlay AS Number in the OMP template prevents redistribution loops by causing OMP to reject routes carrying the local overlay AS number when they are re-advertised back from the LAN side.

WAN Edge Router Deployment

Question

A network administrator is creating an OMP feature template from the vManage GUI to be applied to WAN edge routers. Which configuration attribute will avoid the redistribution of the routes back into the OMP from the LAN side?

Options

  • Aconfigure "Number of Paths Advertised per Prefix"
  • Bconfigure "Overlay AS Number"
  • Cconfigure "Send Backup Paths"
  • Dconfigure "ECMP limit"

Explanation

Configuring the Overlay AS Number in the OMP template prevents redistribution loops by causing OMP to reject routes carrying the local overlay AS number when they are re-advertised back from the LAN side.

Common mistakes.

  • A. 'Number of Paths Advertised per Prefix' controls how many equal-cost OMP paths vSmart advertises per prefix to WAN Edge routers; it does not affect route redistribution loop prevention from the LAN side.
  • C. 'Send Backup Paths' enables OMP to advertise secondary paths in addition to the best path for faster failover; it is unrelated to preventing LAN-to-OMP redistribution loops.
  • D. 'ECMP limit' controls the maximum number of equal-cost paths used for load balancing within OMP; it does not prevent route redistribution from the service side back into the OMP overlay.

Concept tested. OMP Overlay AS Number for redistribution loop prevention

Reference. https://www.cisco.com/c/en/us/td/docs/routers/sdwan/configuration/routing/ios-xe-17/routing-book-xe/m-omp.html

Topics

#OMP#Route Redistribution#Loop Prevention#Overlay AS

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