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300-420 · Question #165

Refer to the exhibit. AS65533 and AS65530 are announcing a partial Internet routing table as well as their IP subnets. An architect must create a design that ensures AS64512 become a transit AS…

The correct answer is D. no-export. The architect needs to configure AS64512 to function as a transit AS, ensuring that routes learned from its peers are appropriately filtered for onward advertisement to other external ASs.

Advanced Addressing and Routing Solutions

Question

Refer to the exhibit. AS65533 and AS65530 are announcing a partial Internet routing table as well as their IP subnets. An architect must create a design that ensures AS64512 become a transit AS. Which filtering solution must the architect choose?

Exhibit

300-420 question #165 exhibit

Options

  • AMaximum-prefix
  • BNo-advertise
  • CNext-hop
  • Dno-export

How the community answered

(37 responses)
  • A
    14% (5)
  • B
    3% (1)
  • C
    11% (4)
  • D
    73% (27)

Why each option

The architect needs to configure AS64512 to function as a transit AS, ensuring that routes learned from its peers are appropriately filtered for onward advertisement to other external ASs.

AMaximum-prefix

`Maximum-prefix` is used to limit the number of prefixes accepted from a BGP peer, protecting the router from routing table overflow, and does not control transit behavior or route propagation policies.

BNo-advertise

The `no-advertise` BGP community attribute prevents a route from being advertised to any other BGP peer, whether internal or external, which is a more restrictive action than typically desired for a transit AS.

CNext-hop

Modifying the `next-hop` attribute affects how traffic reaches a destination but is not a filtering solution that controls whether routes are propagated to make an AS a transit network.

Dno-exportCorrect

The `no-export` BGP community attribute prevents routes tagged with it from being advertised outside of the local AS, which is essential for a transit AS to control route propagation and ensure routes remain within its boundary when necessary.

Concept tested: BGP community for route propagation control

Source: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_bgp/configuration/xe-16-10/bgp-xe-16-10-book/bgp-route-maps-comm-attr.html

Topics

#BGP Communities#BGP Route Filtering#Transit AS

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