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300-510 · Question #287

Refer to the exhibit. A network engineer at a large ISP with an employee ID 487694052 started to configure OSPF on two routers. The engineer notices that router 1 learned about network 20.20.20.0/24 f

The correct answer is A. Replace the router 1 OSPF network configuration with network 10.10.10.0 0.0.0.255 area 0.. Router 1 has an incorrect OSPF network statement that prevents it from advertising 10.10.10.0/24 to its neighbor; correcting the wildcard mask and area designation resolves the asymmetric advertisement.

Unicast Routing

Question

Refer to the exhibit. A network engineer at a large ISP with an employee ID 487694052 started to configure OSPF on two routers. The engineer notices that router 1 learned about network 20.20.20.0/24 from router 2, but router 2 did not learn about 10.10.10.0/24 from router 1 Layer 2 and Layer 3 connectivity are working between the two routers and the physical connection between the devices is functioning. Which action must the engineer take to resolve the issue?

Exhibit

300-510 question #287 exhibit

Options

  • AReplace the router 1 OSPF network configuration with network 10.10.10.0 0.0.0.255 area 0.
  • BOn router 1 configure a route map with a distribution list for the 10 10.10 0/24 network.
  • CReplace the router 2 OSPF network configuration with network 10.10.10.0 0.0.0.255 area
  • DOn router 2 configure a route map with a distribution list for the 10.10.10.0/24 network

How the community answered

(61 responses)
  • A
    89% (54)
  • B
    2% (1)
  • C
    7% (4)
  • D
    3% (2)

Why each option

Router 1 has an incorrect OSPF network statement that prevents it from advertising 10.10.10.0/24 to its neighbor; correcting the wildcard mask and area designation resolves the asymmetric advertisement.

AReplace the router 1 OSPF network configuration with network 10.10.10.0 0.0.0.255 area 0.Correct

The OSPF network statement on router 1 must be corrected to 'network 10.10.10.0 0.0.0.255 area 0' so that the 10.10.10.0/24 interface is matched and included in OSPF area 0 advertisements. An incorrect wildcard mask or area value in the existing statement causes OSPF to skip that interface entirely, explaining why router 2 never receives the route. Since router 2 is already successfully advertising 20.20.20.0/24, the misconfiguration is isolated to router 1's network statement.

BOn router 1 configure a route map with a distribution list for the 10 10.10 0/24 network.

A distribution list with a route map on router 1 is used to filter redistributed external routes, not to fix a missing OSPF network advertisement caused by an incorrect network statement.

CReplace the router 2 OSPF network configuration with network 10.10.10.0 0.0.0.255 area

The problem resides on router 1 (it is not advertising its network), so modifying router 2's OSPF network statement would not cause router 1 to begin advertising 10.10.10.0/24.

DOn router 2 configure a route map with a distribution list for the 10.10.10.0/24 network

Configuring a distribution list on router 2 would only filter routes received by router 2 and does not address the root cause of router 1 failing to originate the LSA for 10.10.10.0/24.

Concept tested: OSPF network statement wildcard mask misconfiguration

Source: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_ospf/configuration/xe-16/iro-ospf-xe-16-book/iro-cfg-ospf.html

Topics

#OSPF configuration#Network advertisement#Routing protocol troubleshooting#Wildcard masks

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