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350-501 · Question #263

An engineer is implementing a route map to support redistribution within BGP. The route map must be configured to permit all unmatched routes. Which action must the engineer perform to complete this…

The correct answer is D. Include a permit statement as the last entry. To ensure that all routes not explicitly matched by specific statements are permitted in a route map, an engineer must include a general permit statement as the very last entry in the route map. This final entry overrides the implicit deny at the end of every route map.

Networking

Question

An engineer is implementing a route map to support redistribution within BGP. The route map must be configured to permit all unmatched routes. Which action must the engineer perform to complete this task?

Options

  • AInclude a permit statement as the first entry.
  • BRemove the implicit deny entry.
  • CInclude at least one explicit deny statement.
  • DInclude a permit statement as the last entry.

How the community answered

(47 responses)
  • A
    2% (1)
  • B
    4% (2)
  • C
    9% (4)
  • D
    85% (40)

Why each option

To ensure that all routes not explicitly matched by specific statements are permitted in a route map, an engineer must include a general permit statement as the very last entry in the route map. This final entry overrides the implicit deny at the end of every route map.

AInclude a permit statement as the first entry.

Including a permit statement as the first entry would permit all routes from the start, effectively making any subsequent match/deny statements irrelevant for many routes.

BRemove the implicit deny entry.

The implicit deny entry cannot be removed from a route map; it's an inherent behavior. It must be explicitly overridden by a final permit statement.

CInclude at least one explicit deny statement.

Including at least one explicit deny statement doesn't change the behavior for unmatched routes; it only ensures specific routes are denied. Unmatched routes would still hit the implicit deny unless a final permit is present.

DInclude a permit statement as the last entry.Correct

Route maps, by default, have an implicit deny statement at the end. This means if a route does not match any explicit permit or deny statements, it will be denied. To permit all unmatched routes, a generic permit statement with no match criteria should be added as the final entry in the route map, effectively catching all traffic that has not been explicitly denied or permitted by previous statements.

Concept tested: Route map implicit deny and permit all configuration

Source: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_static/configuration/15-mt/irs-15-mt-book/irs-config-route-maps.html

Topics

#Route Maps#BGP Redistribution#Implicit Deny Logic#Policy Routing

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