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Exam JN0-648 topic 1 question 54 discussion

Actual exam question from Juniper's JN0-648
Question #: 54
Topic #: 1
[All JN0-648 Questions]

Click the Exhibit button.

Referring to the exhibit, how is R1 learning the route from R2?

  • A. R2 has an export policy with external type 2 configured.
  • B. R2 has interface ge-0/0/2 configured as a passive interface under OSPFv3.
  • C. R2 has interface ge-0/0/2 configured in another area under OSPFv3.
  • D. R2 has an export policy with external type 1 configured.
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Suggested Answer: D 🗳️

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nushadu
3 years, 5 months ago
tested in the LAB, "metric " changed from 0 -> 10 (0 was in type 2, 10 in type 1) ed@vMX_R2> show route protocol ospf 10.0.13.0/24 inet.0: 19 destinations, 23 routes (19 active, 0 holddown, 0 hidden) + = Active Route, - = Last Active, * = Both 10.0.13.0/24 *[OSPF/150] 00:01:30, metric 0, tag 0 > to 10.0.0.1 via em0.2 ed@vMX_R2> ed@vMX_R2> ed@vMX_R2> show route protocol ospf 10.0.13.0/24 inet.0: 19 destinations, 23 routes (19 active, 0 holddown, 0 hidden) + = Active Route, - = Last Active, * = Both 10.0.13.0/24 *[OSPF/150] 00:00:12, metric 10, tag 0 > to 10.0.0.1 via em0.2
upvoted 2 times
nushadu
3 years, 5 months ago
ed@vMX-PE1# show | compare [edit policy-options policy-statement direct-to-ospf term 10 then] + external { + type 1; + } [edit] ed@vMX-PE1# commit commit complete [edit] ed@vMX-PE1# ...icy-options policy-statement direct-to-ospf | display set set policy-options policy-statement direct-to-ospf term 10 from protocol direct set policy-options policy-statement direct-to-ospf term 10 then external type 1 set policy-options policy-statement direct-to-ospf term 10 then accept [edit] ed@vMX-PE1# run show ospf database external advertising-router 1.1.1.1 OSPF AS SCOPE link state database Type ID Adv Rtr Seq Age Opt Cksum Len Extern *1.1.1.11 1.1.1.1 0x80000002 78 0x22 0xca55 36 Extern *10.0.12.0 1.1.1.1 0x80000002 78 0x22 0x56c1 36 Extern *10.0.13.0 1.1.1.1 0x80000002 78 0x22 0x4bcb 36 Extern *192.168.13.0 1.1.1.1 0x80000002 78 0x22 0xab0 36 [edit] ed@vMX-PE1#
upvoted 2 times
nushadu
3 years, 5 months ago
so, yes, "A" is the correct answer. because external (pref 150) and type 2 (metric 0) ed@vMX-PE1# show protocols ospf | display set set protocols ospf traffic-engineering set protocols ospf area 0.0.0.2 interface lo0.0 passive set protocols ospf area 0.0.0.2 interface lo0.0 metric 500 set protocols ospf area 0.0.0.2 interface em0.2 interface-type p2p set protocols ospf area 0.0.0.2 interface em0.2 bfd-liveness-detection minimum-interval 1000 set protocols ospf traceoptions file ospf_log.txt set protocols ospf traceoptions file size 10k set protocols ospf traceoptions file files 3 set protocols ospf traceoptions file world-readable set protocols ospf traceoptions flag error set protocols ospf export direct-to-ospf set protocols ospf reference-bandwidth 10g [edit] ed@vMX-PE1#
upvoted 2 times
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M_A_T
3 years, 6 months ago
type 1 externall: cost to reach the gateway is added to the configured cost at the gateway. Since the metric (cost) is 0 the configures cost is 0 and the cost to reach the gateway is 0. That brings me to the conclusion a type 2 route is used (which is default, but that's not the point).
upvoted 1 times
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SB13
4 years, 6 months ago
Type 1 external metrics are equivalent to the link-state metric, where the cost is equal to the sum of the internal costs plus the external cost. This means that Type 1 external metrics include the external cost to the destination as well as the cost (metric) to reach the AS boundary router. Type 2 external metrics are greater than the cost of any path internal to the AS. Type 2 external metrics use only the external cost to the destination and ignore the cost (metric) to reach the AS boundary router. By default, OSPF uses the Type 2 external metric.
upvoted 3 times
Gdjskiejdn
4 years, 5 months ago
Agree so; A. R2 has an export policy with external type 2 configured.
upvoted 4 times
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takhira
4 years, 6 months ago
Shoudn't be A? By default external route is type 2.
upvoted 3 times
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