Cisco CCNP BSCI Certification Exam Practice Questions:
OSPF Virtual Links, DRs, BDRs, DROTHERs, And More!
By Chris Bryant, CCIE #12933
Passing the 642-901 BSCI exam is tough, so to help you along, here are ten free Cisco CCNP certification exam practice questions on OSPF. Answers and explanations are posted at the bottom of the page.
1. RouterA is the DR for a broadcast segment, with RouterB as the BDR and RouterC as the DROTHER. RouterA is rebooted. While RouterA is rebooting, RouterB becomes the DR and RouterC becomes the BDR. What describes RouterA's role five minutes after it comes back online?
A. RouterA will be the DR.
B. RouterA will be a DROTHER.
C. Router A will be none of these.
D. RouterA will be the BDR.
2. The default AD of OSPF is ____________.
3. If both the ethernet and hub-and-spoke segments shown in the following exhibit are correctly configured, how many BDRs are there in all?
A. Zero
B. One
C. Two
D. Three
4. There are four routers on an OSPF broadcast network segment. If all OSPF settings have been left at the default, how many DROTHERS will be found on the segment?
A. One
B. Two
C. Three
D. Four
E. Zero
5. A virtual link is needed in the network shown in the following exhibit. Which area will be the "transit area"?
A. Area 13.
B. Area 4.
C. Area 34.
D. An additional area must be added, and that area will be the transit area.
E. Area 0, as always.
6. When a DROTHER residing on an ethernet segment detects a change in the network, what does it do?
A. It will send an update reflecting the change to 224.0.0.5.
B. It will send an update reflecting the change to 224.0.0.6.
C. DROTHERs do not send any kind of link change notifications.
D. Since ethernet is a broadcast media, an update reflecting the change will be broadcast.
7. Which of the following does not have to match between potential OSPF neighbors for an adjacency to form?
A. Process ID
B. Link Authentication
C. Hello And Dead Timer Settings
D. Stub Flag Setting
E. The Area Number
8. There are four routers on an OSPF broadcast network. With the default settings, how many of them are listening for packets addressed to 224.0.0.6?
9. The default OSPF cost for a 56kbps serial link is ____________.
10. OSPF uses which of the following formulas to calculate an interface's cost?
A. 100,000,000 / Bandwidth in bits per second
B. 100,000,000 / Bandwidth in kilobits per second
C. 100,000,000 / Bandwidth in megabits per second
D. There is no formula for OSPF cost; it depends solely on the interface type.
11. The default OSPF cost is 1 for which of the following interface types?
A. ATM
B. Token Ring
C. FDDI
D. T1 Serial Link
E. Ethernet, 10 MBPS
F. 100 MBPS Ethernet
G. Asynchronous Serial
H. E1 Serial Link
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Here are the answers!
1. B - RouterA will become a DROTHER, as it will be neither the DR nor the BDR. With OSPF, a DR/BDR election is not held when a router comes online, or when a router that was previously a DR or BDR comes back online.
2. The default administrative distance (AD) of OSPF is 110.
3. B - There will be only one BDR, either R5 or R1, for the ethernet segment. An ethernet segment (or any OSPF broadcast network) will have a DR and BDR; a hub-and-spoke network must have the hub configured as the DR and will have no BDR.
4. B - By default, a broadcast OSPF segment with four OSPF routers will have one DR, one BDR, and two DROTHERS - routers that are neither a DR nor a BDR.
5. C - Area 4's sole router, R4, has no physical interface in Area 0. Therefore, a virtual interface (the virtual link) must be configured from R4 to a router that does. A virtual link will be built between R3 and R4, making Area 34 the transit area.
6. B - A DROTHER on an ethernet segment will send the LSA update to 224.0.0.6, where the DR and BDR will hear it. Those routers are responsible for flooding the change to the rest of the network.
7. A - OSPF process numbers are locally significant only and do not affect adjacencies. The routers must agree on the area number the link is being placed into, the hello and dead timers, and whether the area is a stub area or not (the "stub flag").
8. Two routers, the DR and BDR, are listening for network change notifications sent to 224.0.0.6.
9. OSPF cost: 100,000,000 / bw in bits per second. 100,000,000 /56000 = 1785.
10. OSPF uses the following formula to determine an interface's cost:
100,000,000 / Bandwidth in bits per second.
11. A, C, F - The default OSPF cost is "1" for 100 MBPS Ethernet, ATM, and FDDI.
To your success,
Chris Bryant
CCIE #12933
chris@thebryantadvantage.com
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