350-401 · Question #253
Which BGP command advertises a summary route to prevent link-flap processing by downstream BGP routers?
The correct answer is B. aggregate-address network subnet-mask summary-only. The aggregate-address network subnet-mask summary-only BGP command advertises a summary route while suppressing the advertisement of more specific routes, which helps prevent downstream BGP routers from processing updates caused by link flaps of the specific routes.
Question
Which BGP command advertises a summary route to prevent link-flap processing by downstream BGP routers?
Options
- Aaggregate-address network subnet-mask as-set
- Baggregate-address network subnet-mask summary-only
- Csummary-address network subnet-mask
- Dsummary-address network mask subnet-mask
How the community answered
(34 responses)- A3% (1)
- B76% (26)
- C9% (3)
- D12% (4)
Why each option
The `aggregate-address network subnet-mask summary-only` BGP command advertises a summary route while suppressing the advertisement of more specific routes, which helps prevent downstream BGP routers from processing updates caused by link flaps of the specific routes.
The `as-set` option includes the AS numbers of all components in the aggregate's AS_PATH but does not suppress the specific routes from being advertised.
The `aggregate-address network subnet-mask summary-only` command creates an aggregate route and simultaneously suppresses the advertisement of all more specific routes that fall within that aggregate, effectively hiding individual route instabilities from downstream BGP routers.
`summary-address` is not a standard BGP command for creating aggregate routes; `aggregate-address` is the correct command.
`summary-address` is not a standard BGP command, and the syntax provided is also incorrect.
Concept tested: BGP route aggregation and suppression
Source: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_bgp/configuration/15-s/bgp-15-s-book/bgp-route-agg.html
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