1. A, B, D. As the size of a single-area OSPF network grows, so does the size of the routing table and OSPF
database that have to be maintained. Also, if there is a change in network topology, the OSPF algorithm
has to be rerun for the entire network.
2. B. An autonomous system boundary router (ASBR) is any OSPF router that is connected to an external
routing process (another AS). An ABR, on the other hand, connects one (or more) OSPF areas together to
area 0.
3. B, D, E. In order for two OSPF routers to create an adjacency, the Hello and Dead timers must match, and
they must both be configured into the same area as well as being in the same subnet. Also, if
authentication is configured, that info must match as well.
4. C. The process starts by sending out Hello packets. Every listening router will then add the originating
router to the neighbor database. The responding routers will reply with all of their Hello information so that
the originating router can add them to its own neighbor table. At this point, we will have reached the 2WAY
state—only certain routers will advance beyond this to establish adjacencies.
5. D. If you have multiple links to the same network, you can change the default cost of a link so OSPF will
prefer that link over another with the
ip ospf cost
cost
command.
6. B. In the FULL state, all LSA information is synchronized among adjacent neighbors. OSPF routing can
begin only after the FULL state has been reached. The FULL state occurs after the LOADING state finishes.
7. B, D, E. Configuring OSPFv3 is pretty simple, as long as you know what interfaces you are using on your
router. There are no network statements; OSPFv3 is configured on a per-interface basis. OSPFv2 and
OSPFv3 both use a 32-bit RID, and if you have an IPv4 address configured on at least one interface, you do
not need to manually set a RID when configuring EIGRPv3.
8. B. When OSPF adjacency is formed, a router goes through several state changes before it becomes fully
adjacent with its neighbor. The states are (in order) DOWN, ATTEMPT, INIT, 2WAY, EXSTART, EXCHANGE,
LOADING, and FULL.
9. B. Referred to as a network link advertisement (NLA), Type 2 LSAs are generated by designated routers
(DRs). Remember that a designated router is elected to represent other routers in its network, and it
establishes adjacencies with them. The DR uses a Type 2 LSA to send out information about the state of
other routers that are part of the same network.
10. C. Referred to as summary link advertisements (SLAs), Type 3 LSAs are generated by area border routers.
These ABRs send Type 3 LSAs toward the area external to the one where they were generated. The Type 3
LSA advertises networks, and these LSAs advertise inter-area routes to the backbone area (area 0).
11. D. To see all LSAs a router has learned from its neighbors, you need to see the OSPF LSDB, and you can
see this with the
show ip ospf database
command.
12. B. Based on the information in the question, the cost from R1 to R2 is 4, the cost from R2 to R3 is 15, and
the cost from R3 to R5 is 4. 15 + 4 + 4 = 23. Pretty simple.
13. B, D. Since R3 is connected to area 1 and R1 is connected to area 2 and area 0, the routes advertised from
R3 would show as
OI
, or inter-area routes.
14. A, D, E, F, G. For two OSPF routers to form an adjacency, they must be in the same area, must be in the
same subnet, and the authentication information must match, if configured. You need to also check if an
ACL is set and if a passive interface is configured, and every OSPF router must use a different RID.
15. C. The IOS command
show ip ospf neighbor
shows neighbor router information, such as neighbor ID
and the state of adjacency with the neighboring router.
16. D. The command
show ip ospf
interface
on a default broadcast multi-access network will show you
DRs and BDRs on that network.
17. A, C, D, F. It’s hard to tell from this single output what is causing the problem with the adjacency, but we
need to check the ACL 10 to see what that is doing, verify that the routers are in the same area and in the
same subnet, and see if passive interface is configured with the interface we’re using.
18. B, D, G. The default reference bandwidth is 100 by default, and you can change it under the OSPF process
with the
auto-cost reference bandwidth
number
command, but if you do, you need to configure
this command on all routers in your AS.
19. A, D. An OSPF RID will be used as source of Type 1 LSA, and the router will chose the highest loopback
interface as its OSPF router ID (if available).
20. B, C. With single area OSPF you’d use only a couple LSA types, which can save on bandwidth. Also, you
wouldn’t need virtual links, which is a configuration that allows you to connect an area to another area that
is not area 0.
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