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350-401 · Question #732

Which two statements about OSPF route filtering are true? (Choose two)

The correct answer is A. It can be based on the source router ID. B. It can be based on the external route tag.. OSPF route filtering allows controlling which routes are learned or advertised based on attributes such as the source router ID or external route tags.

Submitted by femi9· Mar 6, 2026Infrastructure

Question

Which two statements about OSPF route filtering are true? (Choose two)

Options

  • AIt can be based on the source router ID.
  • BIt can be based on the external route tag.
  • CIt affects LSA flooding.
  • DIt can be based on the as-path.
  • EIt can be based on distance.

How the community answered

(47 responses)
  • A
    62% (29)
  • C
    21% (10)
  • D
    4% (2)
  • E
    13% (6)

Why each option

OSPF route filtering allows controlling which routes are learned or advertised based on attributes such as the source router ID or external route tags.

AIt can be based on the source router ID.Correct

OSPF routes can be filtered based on the source Router ID (RID) using mechanisms like distribute-lists or route-maps, allowing administrators to control the learning of routes originating from specific OSPF routers.

BIt can be based on the external route tag.Correct

External OSPF routes, specifically Type 5 LSAs, can carry a route tag attribute, which can be leveraged in route-maps or distribute-lists for filtering or applying policies during redistribution or route importation.

CIt affects LSA flooding.

OSPF route filtering primarily affects the routes installed in the routing table, not the flooding of LSAs within an OSPF area, as LSA flooding must occur for all routers to maintain a consistent link-state database.

DIt can be based on the as-path.

OSPF is an Interior Gateway Protocol (IGP) and does not utilize AS-path attributes for route filtering; AS-path is a BGP-specific attribute used in inter-AS routing.

EIt can be based on distance.

While OSPF uses administrative distance for path selection when multiple routing protocols or instances exist, route filtering is not directly based on administrative distance, which is an external preference value.

Concept tested: OSPF route filtering mechanisms

Source: https://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/13670-52.html

Topics

#OSPF#route filtering#LSA flooding#routing policy

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