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Which action must you perform on your OSPF router to so…

You are connecting your OSPF router to your customer’s RIP router and redistributing the customer’s routes
into your OSPF domain. Your OSPF routes is part of an NSSA and the ABR is injecting an OSPF default route,
which you have advertised to your customer. After committing the configuration, you notice a routing loop
between your OSPF router and the customer’s RIP router.
Which action must you perform on your OSPF router to solve this problem?

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A.
Enable Type 7-to-Type 5 LSA conversion.

B.
Set the customer-facing interface to passive.

C.
Convert the area to a stub area.

D.
Change the OSPF external route preference.

Explanation:
Avoid routing loops by changing the OSPF external route preference.
Incorrect Answers:
A: If multiple NSSA ABR routers are present, it is recommended that not all ABRs perform Type 7-to-5
translation to avoid routing loops.
B: We would have to make the interface on the RIP router, the customer router, passive, not the customerfacing interface on the OSPF router.
Note: By default RIP broadcasts are sent from all interfaces. RIP allows us to control this behavior. We can
configure which interface should send RIP broadcast or which not. Once we mark any interface as passive
interface, RIP will stop sending updates from that interface.
https://www.juniper.net/documentation/en_US/junos15.1/topics/topic-map/ospf-stub-and-not-sostubby-areas.html

2 Comments on “Which action must you perform on your OSPF router to so…

  1. fe says:

    default-lsa—Configures the ABR to generate a default route into the NSSA.

    In my lab I checked that the default is generate as an OSPF EXTERNAL route by ABR.
    0.0.0.0/0 [OSPF/150] 00:01:09, metric 2, tag 0
    > to 10.99.12.20 via ge-0/0/1.0

    OSPF database, Area 0.0.0.1
    Type ID Adv Rtr Seq Age Opt Cksum Len

    Summary 10.99.50.0 10.2.2.2 0x80000001 389 0x20 0xd9b4 28
    NSSA 0.0.0.0 10.2.2.2 0x80000001 276 0x20 0x51d 36 >>>>>>>>

    https://www.juniper.net/documentation/en_US/junos/topics/example/ospf-not-so-stubby-area-configuring.html

    RIP 100
    OSPF AS external routes 150
    OSPF internal route 10

    https://www.juniper.net/documentation/en_US/junos/topics/reference/general/routing-protocols-default-route-preference-values.html

    set protocols ospf preference xx external-preference xxx

    https://www.juniper.net/documentation/en_US/junos/topics/example/ospf-route-preference-configuring.html




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  2. Chuck says:

    Option D, Final answer.

    To prevent routing loops in OSPF, being able to use multiple available paths to calculate an AS external route can prevent routing loops.

    To do this;

    Enter OSPF configuration mode and set the external and internal routing preferences.

    set protocols ospf preference external-preference

    In real-life, use a “show protocols ospf” to see the preferences configured, otherwise use the defaults.

    OSPF internal route preference 10
    OSPF AS external routes preference 150




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