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ENSLD 300-420 CCNP Enterprise Design > Chapter 4 - OSPF, BGP, and Route Manipulation > Flashcards

Chapter 4 - OSPF, BGP, and Route Manipulation Flashcards

1
Q

In OSPF, where does summarization of internal routes occur?

  1. Backbone router
  2. Designated router
  3. ABR
  4. ASBR
A

C.

In OSPF, summarization of internal routes is performed on the ABRs.

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2
Q

Which BGP metric is used to influence the path of outbound traffic?

  1. AS_Path
  2. Origin
  3. MED
  4. Weight
A

D.

Weight is assigned locally on a router to specify a preferred path if multiple paths exist out of a router for a destination.

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3
Q

What is an ASBR?

  1. Area border router
  2. Autonomous system boundary router
  3. Auxiliary system border router
  4. Area system border router
A

B.

OSPF defines the ASBR as the router that injects external routes into the OSPF autonomous system.

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4
Q

What is the OSPFv2 link-state advertisement (LSA) type for autonomous system external LSAs?

  1. Type 1
  2. Type 2
  3. Type 3
  4. Type 4
  5. Type 5
A

E. OSPFv2 Type 5 LSAs are autonomous system external LSAs.

  • LSA Type 1 - Router LSA
    • Each router in an area will generate a type 1 LSA - one for each area it is connected to. It contains the routers RID and all the routers IP addresses for interfaces attached to the specific area. It is not flooded beyond the area in which it was originated.
    • The show ip ospf database router command will show the type 1 LSAs in a routers LSDB.
  • LSA Type 2 - Network LSA
    • The Designated Router (DR), on shared segment, originates type 2 LSAs containing the interface IP address of the DR and a list of the DRs connected neighbors in the area. The type 2 LSA is only propagated in the area it is originated in and only by the DR.
    • The show ip ospf database network command will show the type 2 LSAs in the routers LSDB.
  • LSA Type 3 - Summary LSA
    • The summary LSA is originate by an Area Border Router (ABR) and advertises a prefix from one area into another. It will advertise the destination prefixes from a non-backbone area into the backbone including the metric from the ABR to the destination. It will do this for each prefix known, but it can instructed to replace the individual prefixes with a less-specific summary address and thus the ABR is one of the few places, in an OSPF network, that allows for network summarization.
    • The show ip ospf database summary command will show the type 3 LSAs in the routers LSDB.
  • LSA Type 4 - ASBR Summary LSA
    • Originated by an ABR, this type of LSA contains the host address of an Autonomous System Border Router (ASBR) in an area and the cost to reach it from the ABR. This is sent along with the LSA type 5 to allow routers outside the area, of the ASBR, to find a path to the ASBR, redistributing an external route into OSPF. This is not needed for routers in the same area as the ASBR due to the presence of the type 1 and 2 LSAs.
    • The show ip ospf database asbr-summary command will show the type 4 LSAs in the routers LSDB.
  • LSA Type 5 - AS-External LSA
    • The type 5 LSA is originated by an ASBR and contains the E1 or E2 external route information for a prefix redistributed into the OSPF process from another AS (for example BGP, EIGRP or maybe just a connected interface, to name but a few options). Routers not residing in the same area as the ASBR will need an ABR to originate a type 4 LSA containing the information needed to compute the SPF tree to the ASBR.
    • The show ip ospf database external command will show the type 5 LSAs in the routers LSDB.
  • LSA Type 6 - Group Membership
    • Used in Multicast OSPF. The feature is unsupported in Cisco IOS (as far as I know).
  • LSA Type 7 - NSSA External
    • The type 7 LSA is flooded in an area by an ASBR in a Not-So-Stubby-Area (NSSA). An ABR will convert the type 7 LSA into a type 5 LSA for other areas. The type 7 LSA allows other routers in the same NSSA area to learn the external routes advertised by the ASBR as one of the features of an NSSA type area is to filter out type 5 LSAs.
    • The show ip ospf database nssa-external command will show the type 5 LSAs in the routers LSDB.
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5
Q

What address do you use to multicast to the OSPFv2 designated router (DR)?

  1. 224.0.0.1
  2. 224.0.0.5
  3. 224.0.0.6
  4. 224.0.0.10
A

C.

OSPFv2 routers use 224.0.0.6 to communicate with DRs.

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6
Q

OSPF Type 1 LSAs are flooded ______.

  1. to the OSPF area
  2. to the OSPF domain
  3. from the area to the OSPF backbone
  4. through the virtual link
A

A.

Type 1 LSAs (router LSAs) are forwarded to all routers within an OSPF area.

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7
Q

What OSPFv3 LSA carries address prefixes?

  1. Network LSA
  2. Summary LSA
  3. Interarea-router LSA
  4. Intra-area-prefix LSA
A

D. Intra-area-prefix LSAs carry IPv6 prefixes associated with a router, a stub network, or an associated transit network segment.

OSPFv3 LSA types:

  • Router LSA—Type-1 LSA, originated by all routers. This LSA describes the collected states of the router’s interfaces to an area, and is flooded throughout a single area only.
  • Network LSA—Type-2 LSA, originated for broadcast and NBMA networks by the DR. This LSA contains the list of routers connected to the network, and is flooded throughout a single area only.
  • Inter-Area-Prefix LSA—Type-3 LSA, originated by ABRs and flooded throughout the LSA’s associated area. Each Inter-Area-Prefix LSA describes a route with IPv6 address prefix to a destination outside the area, yet still inside the AS.
  • Inter-Area-Router LSA—Type-4 LSA, originated by ABRs and flooded throughout the LSA’s associated area. Each Inter-Area-Router LSA describes a route to ASBR.
  • AS External LSA—Type-5 LSA, originated by ASBRs, and flooded throughout the AS, except stub areas and Not-So-Stubby Areas (NSSAs). Each AS External LSA describes a route to another AS. A default route can be described by an AS External LSA.
  • NSSA LSA—Type-7 LSA, originated by ASBRs in NSSAs and flooded throughout a single NSSA. NSSA LSAs describe routes to other ASs.
  • Link LSA—Type-8 LSA. A router originates a separate Link LSA for each attached link. Link LSAs have link-local flooding scope. Each Link LSA describes the IPv6 address prefix of the link and Link-local address of the router.
  • Intra-Area-Prefix LSA—Type-9 LSA. Each Intra-Area-Prefix LSA contains IPv6 prefix information on a router, stub area, or transit area information, and has area flooding scope. It was introduced because Router LSAs and Network LSAs contain no address information.
  • Grace LSA—Type-11 LSA, generated by a GR restarter at reboot and transmitted on the local link. The GR restarter describes the cause and interval of the reboot in the Grace LSA to notify its neighbors that it performs a GR operation.
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8
Q

What protocol do you use to exchange IP routes between autonomous systems?

  1. IGMP
  2. eBGP
  3. EIGRP
  4. OSPF
A

B.

You use External Border Gateway Protocol (eBGP) to exchange routes between autonomous systems.

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9
Q

Where should routes be summarized?

  1. On the core routers
  2. On the distribution routers
  3. On the access routers
  4. None of the above
A

B.

It is a best practice to summarize routes on the distribution routers toward the core.

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10
Q

What is the administrative distance of External BGP routes?

  1. 20
  2. 100
  3. 110
  4. 200
A

A.

The administrative distance of eBGP routes is 20. The administrative distance of Internal BGP (iBGP) routes is 200.

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11
Q

What kind of information is sent in an OSPF LSA?

A

In OSPF, each router sends link-state advertisements (LSAs) about itself and its links to all other routers in the area.

Note that it does not send routing tables but rather sends link-state information about its interfaces.

Then, each router individually calculates the best routes to the destination by running the SPF algorithm. Each OSPF router in an area maintains an identical database describing the area’s topology. The routing table at each router is individually constructed using the local copy of this database to construct a shortest-path tree.

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12
Q

T/F: OSPFv2 is a classful routing protocol that permits the use of VLSM.

A

False.

OSPFv2 is a classless routing protocol that permits the use of VLSM.

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13
Q

T/F: With Cisco routers, OSPF also supports equal-cost multipath load balancing and neighbor authentication.

A

True

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14
Q

OSPF uses multicast addresses to communicate between routers. OSPF uses IP protocol number ___.

A

OSPF uses multicast addresses to communicate between routers. OSPF uses IP protocol 89.

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15
Q

The metric that OSPFv2 uses is called _____. It is an unsigned 16-bit integer in the range 1 to ________.

A

The metric that OSPFv2 uses is cost. It is an unsigned 16-bit integer in the range 1 to 65,535.

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16
Q

T/F: OSPF performs a summation of the costs to reach a destination; the lowest cost is the preferred path.

A

True.

Table 4-2 shows some sample interface metrics.

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17
Q

OSPF uses _____ packets for neighbor discovery.

A

OSPF uses Hello packets for neighbor discovery.

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18
Q

True or false: A router needs to have all its interfaces in Area 0 to be considered an OSPF backbone router.

A

False. A router with one or more interfaces in Area 0 is considered an OSPF backbone router.

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19
Q

True or false: OSPF and IS-IS use a designated router in multiaccess networks.

A

True

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20
Q

Which multicast addresses do OSPFv2 routers use?

A

224.0.0.5 for ALLSPFRouters and 224.0.0.6 for ALLDRouters.

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21
Q

Which multicast addresses do OSPFv3 routers use?

A

FF02::5 for ALLSPFRouters and FF02::6 for ALLDRouters.

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22
Q
  1. What is the Cisco administrative distance of OSPF?
A
  1. The administrative distance of OSPF is 110.
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23
Q

Which OSPFv2 router type generates the OSPF Type 3 LSA?

A

OSPF ABRs generate the Type 3 summary LSA for ABRs.

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24
Q

Which OSPFv2 router type generates the OSPF Type 2 LSA?

A

OSPF DRs generate Type 2 network LSAs.

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25
Q

What is included in an OSPFv2 Type 1 Router LSA?

A

Included are the router’s links, interfaces, link states, and costs.

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26
Q

True or false: The router with the lowest priority is selected as the OSPF DR.

A

False. The router with the highest priority is selected as the OSPF designated router.

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27
Q

True or false: You use iBGP to exchange routes between different autonomous systems.

A

False. You use eBGP to exchange routes between different autonomous systems.

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28
Q

True or false: eBGP and iBGP redistribute automatically on a router if the BGP peers are configured with the same autonomous system number.

A

True.

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29
Q

eBGP routes have an administrative distance of ____, and iBGP routes have an administrative distance of ____.

A

20, 200.

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30
Q

Match each routing protocol with its description.

  1. EIGRP
  2. OSPFv2
  3. RIPv2
  4. BGP
  5. Distance vector protocol used at the edge of the network
  6. IETF link-state protocol used in the network core
  7. Hybrid protocol used in the network core
  8. Path vector protocol
A

i = C

ii = B

iii = A

iv = D

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31
Q

Which routing protocol do you use in the core of a large enterprise network that supports VLSM for a network with a mix of Cisco and non-Cisco routers?

A

OSPF. Although RIPv2 and EIGRP support VLSM, RIPv2 is no longer recommended. EIGRP is not supported on non-Cisco router.

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32
Q

What is the benefit of designing for stub areas?

A

You do not need to flood external LSAs into the stub area, and not doing this flooding reduces LSA traffic.

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33
Q

What constraint does the OSPF network design have for traffic traveling between areas?

A

All traffic from one area must travel through Area 0 (the backbone) to get to another area.

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34
Q

How is OSPFv3 identified as the upper-layer protocol in IPv6?

A

OSPFv3 is identified as IPv6 Next Header 89.

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35
Q

Which routing protocol or protocols are recommended for large enterprise networks?

  1. RIPv2
  2. OSPFv2
  3. EIGRP
  4. IS-IS
  5. A and B
  6. B and C
  7. B and D
  8. A, B, C, and D
A

F. EIGRP and OSPFv2 are recommended for large enterprise networks.

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36
Q

What OSPFv3 LSA has LS type 0x0008?

  1. Router LSA
  2. Interarea-router LSA
  3. Link LSA
  4. Intra-area-prefix LSA
A

C. Link LSAs are flooded to the local link.

OSPFv3 LSA types

Router LSA—Type-1 LSA, originated by all routers. This LSA describes the collected states of the router’s interfaces to an area, and is flooded throughout a single area only.

Network LSA—Type-2 LSA, originated for broadcast and NBMA networks by the DR. This LSA contains the list of routers connected to the network, and is flooded throughout a single area only.

Inter-Area-Prefix LSA—Type-3 LSA, originated by ABRs and flooded throughout the LSA’s associated area. Each Inter-Area-Prefix LSA describes a route with IPv6 address prefix to a destination outside the area, yet still inside the AS.

Inter-Area-Router LSA—Type-4 LSA, originated by ABRs and flooded throughout the LSA’s associated area. Each Inter-Area-Router LSA describes a route to ASBR.

AS External LSA—Type-5 LSA, originated by ASBRs, and flooded throughout the AS, except stub areas and Not-So-Stubby Areas (NSSAs). Each AS External LSA describes a route to another AS. A default route can be described by an AS External LSA.

NSSA LSA—Type-7 LSA, originated by ASBRs in NSSAs and flooded throughout a single NSSA. NSSA LSAs describe routes to other ASs.

Link LSA—Type-8 LSA. A router originates a separate Link LSA for each attached link. Link LSAs have link-local flooding scope. Each Link LSA describes the IPv6 address prefix of the link and Link-local address of the router.

Intra-Area-Prefix LSA—Type-9 LSA. Each Intra-Area-Prefix LSA contains IPv6 prefix information on a router, stub area, or transit area information, and has area flooding scope. It was introduced because Router LSAs and Network LSAs contain no address information.

Grace LSA—Type-11 LSA, generated by a GR restarter at reboot and transmitted on the local link. The GR restarter describes the cause and interval of the reboot in the Grace LSA to notify its neighbors that it performs a GR operation.

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37
Q

Which routing protocol or protocols have fast convergence for IPv4 networks?

  1. BGP
  2. OSPFv2
  3. EIGRP
  4. RIPv2
  5. B and C
  6. B, C, and D
  7. A, B, and C
A

E. EIGRP and OSPFv2 have fast convergence.

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38
Q

Which routing protocol or protocols have fast convergence for IPv6 networks?

  1. RIPng
  2. OSPFv3
  3. EIGRP for IPv6
  4. RIPv2
  5. MP-BGP
  6. B and C
  7. B, C, and D
  8. B, C, and E
A

F. EIGRP for IPv6 and OSPFv3 have fast convergence for IPv6 networks.

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39
Q

2A retail chain has about 800 stores that connect to the headquarters and a backup location. The company wants to limit the amount of routing traffic on the WAN links. What routing protocol or protocols are recommended?

  1. RIPv1
  2. RIPv2
  3. OSPFv2
  4. EIGRP
  5. IS-IS
  6. BGP
  7. B, C, and D
  8. C and D
  9. C, D, and E
A

H. RIPv1 and RIPv2 generate periodic routing traffic. IS-IS is used in SP networks. BGP is used for external networks.

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40
Q

If OSPF is enabled on all routers in Figure 4-26 with the default metrics unchanged, what path is taken?

  1. Path 1
  2. Path 2
  3. Unequal-cost load balancing with Path 1 and Path 2
  4. Equal-cost load balancing with Path 1 and Path 2
A

B.

From Router A, the OSPF cost for Path 1 is 10^8 / 256 kbps = 390. The OSPF cost for Path 2 is (10^8 / 1536 kbps) + (10^8 / 1024 kbps) + (10^8 / 768 kbps) = 65 + 97 + 130 = 292. OSPF selects Path 2 because it has a lower cost.

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41
Q

Identify the OSPF router types shown in Figure 4-27.

  1. Router A = _______
  2. Router B = _______
  3. Router C = _______
  4. Router D = _______
  5. Router E = _______
  6. Router F = _______
A

Router A = internal

Router B = ABR

Router C = backbone

Router D = ASBR

Router E = ABR

Router F = internal.

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42
Q

Match each BGP attribute with its description.

  1. Local preference
  2. MED
  3. Autonomous system path
  4. Next hop
  5. IP address
  6. Indicates the path used to exit the autonomous system
  7. Tells external BGP peers the preferred path into the autonomous system
  8. List of ASNs
A

i = B

ii = C

iii = D

iv = A

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43
Q

Which Cisco feature can you use instead of local preference to influence the selected path to external BGP routers?

A

Weight. Weight is Cisco specific and configured locally and is not exchanged in BGP updates.

On the other hand, the local preference attribute attribute is exchanged between iBGP peers and is configured at the gateway router.

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44
Q

What is the purpose of route reflectors?

A

Route reflectors reduce the number of iBGP logical mesh connections.

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45
Q

When BGP confederations are used, which number do external peers see?

A

External peers see the the external AS. The internal private AS numbers in the sub-ASes are used only within the confederation.

To reduce the number of IBGP peerings there are two techniques:

  • Confederations
  • Route Reflector
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46
Q

With ____________, all routers peer with each other within each private autonomous system. With __________, client routers peer only with the reflector.

A

BGP confederations, route reflectors.

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47
Q

Which of the following is the order of attributes that BGP uses to select a best path?

  1. Origin, lowest IP, autonomous system path, weight, local preference, MED
  2. Weight, local preference, originate, AS path, origin code, MED, path, lowest IP
  3. Lowest IP, autonomous system path, origin, weight, MED, local preference
  4. Weight, origin, local preference, autonomous system path, MED, lowest IP
A

B. The correct order of BGP path selection is weight, local preference, originate (locally originated routes), autonomous system path, ORIGIN Code (IGP > EGP > Incomplete), MED, Path(external over internal) and lowest IP address(RID).

“We Love Oranges AS Oranges Mean Pure Refreshment”

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48
Q

What of the following should be used to summarize the networks 10.150.80.0/23, 10.150.82.0/24, 10.150.83.0/24, and 10.150.84.0/22?

  1. 10.150.80.0/23, 10.150.82.0/23, and 10.150.84.0/22
  2. 10.150.80.0/22 and 10.150.84/22
  3. 10.150.80.0/21
  4. 10.150.80.0/20
A

C.

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49
Q

Which of the following best describes route summarization?

  1. Grouping contiguous addresses to advertise a large Class A network
  2. Grouping noncontiguous addresses to advertise a larger network
  3. Grouping contiguous addresses to advertise a larger network
  4. Grouping Internet addresses
A

C.

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50
Q

Which OSPF area allows redistribution of external routes while preventing propagation of Type 5 LSAs?

  1. Area 0
  2. Stub area
  3. Not-so-stubby area
  4. ABR
  5. Area 1 over a virtual link
A

C.

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51
Q

Which protocol is commonly used to connect to an ISP?

  1. RIPv2
  2. OSPF
  3. EIGRP
  4. BGP
A

D. BGP.

52
Q

Which of the following statements are true regarding OSPF? (Choose two.)

  1. ABRs require manual configuration for summarization.
  2. ABRs automatically summarize.
  3. External routes are injected into the autonomous system via the ABR.
  4. External routes are injected into the autonomous system via the ASBR.
A

A and D.

53
Q

Which routing protocol is recommended for large IPv6 multivendor networks?

  1. RIPng
  2. OSPFv3
  3. EIGRP for IPv6
  4. BGP
A

B.

54
Q

As a network designer, you need to influence the outbound routing towards your ISP. Which of the following are BGP options to do this?

  1. AS_Path, local preference, weight
  2. MED, local preference, weight
  3. AS_Path, BGP communities, MED
  4. BGP communities, local preference, MED
A

A.

55
Q

As a network designer, you need to influence the inbound routing of traffic coming from your ISP. Which of the following are BGP options to do this?

  1. AS_Path, local preference, weight
  2. MED, local preference, weight
  3. AS_Path, BGP communities, MED
  4. BGP communities, local preference, MED
A

C.

56
Q

Which statements are correct? (Choose two.)

  1. The Dijkstra algorithm is used by both OSPF and IS-IS to calculate the shortest best path.
  2. IS-IS is a proprietary protocol. OSPF is a standards-based protocol.
  3. OSPF is used only on enterprise networks, and IS-IS is used only by service providers.
  4. ISIS boundaries are links; OSPF area boundaries are within the routers.
A

A and D.

57
Q

In Figure 4-28, where should route redistribution occur?

  1. R1
  2. R2
  3. R3
  4. R4
  5. R5
A

D. R4.

58
Q

Where should you configure BGP?

  1. Routers A and B
  2. Routers C and D
  3. Routers A, B, C, and D
  4. Routers A and C
A

B. BGP should be configured between AS 100 and AS 500.

59
Q

On which router should you configure redistribution for OSPF and EIGRP?

  1. Router A only
  2. Router B only
  3. Routers A and B
  4. None; redistribution occurs automatically
A

C. Both Routers A and B perform the redistribution with route filters to prevent route feedback.

60
Q

To announce the networks from AS 100 to AS 500, which routing protocols should you redistribute into BGP?

  1. OSPF only
  2. EIGRP only
  3. OSPF and EIGRP
  4. iBGP
A

B. The OSPF routes are redistributed into EIGRP. Then you can redistribute EIGRP routes into BGP.

61
Q

Which two BGP attributes are well-known discretionary?

  1. AS_Path and next hop
  2. MED and origin
  3. Aggregator and community
  4. Atomic aggregate and local preference
A

D. Atomic aggregate and local preference are BGP well-known discretionary attributes.

62
Q
  1. Which two BGP attributes are well-known mandatory?
  2. AS_Path and next hop
  3. MED and origin
  4. Aggregator and community
  5. Atomic aggregate and local preference
A

A. AS_Path and next hop

AS_Path and next hop are BGP well-known discretionary BGP attributes.

Origin is also a well-known discretionary BGP attribute, butMED is optional nontransitive.

63
Q

Which two BGP attributes are optional transitive?

  1. AS_Path and next hop
  2. MED and origin
  3. Aggregator and community
  4. Atomic aggregate and local preference
A

C. Aggregator and community are BGP optional transitive attributes.

64
Q

The IP address of the eBGP peer of a router is reached via OSPF. Which condition should be avoided that might cause the BGP peers to flap?

  1. The OSPF Area 0 is not transverse network to reach the eBGP peer.
  2. The BGP peer address is also sent via the BGP peer.
  3. BGP multipath is not configured.
  4. eBGP peers cannot be configured over OSPF.
A

B. The IP address of the BGP peer might be in the OSPF routes and not in the eBGP routes.

65
Q

Which of the following is true about iBGP?

  1. iBGP is preferred over eBGP when connecting to an ISP.
  2. iBGP carries eBGP attributes that otherwise would be lost in IGP.
  3. iBGP’s administrative distance is 20.
  4. iBGP peers need to be directly connected.
A

B. When used within an AS, iBGP carries eBGP attributes that otherwise would be lost if eBGP were redistributed into an IGP.

66
Q

What is the default metric used when redistributing OSPF into EIGRP?

  1. 0
  2. 1
  3. Cost
  4. Infinity
A

D. OSPF metrics are not automatically converted into EIGRP metrics. If an EIGRP metric is not defined, then infinity is assigned to the redistributed routes, which are thus not injected into the routing table.

67
Q

What type of LSA is produced by every DR on every broadcast or NBMA network. It lists all the routers in the multiaccess network. This LSA type is contained within an area.

A

Type 2 - Nework LSA.

68
Q

What type of LSA is originated by ABRs. Sent into an area by the ABR to advertise the IP addresses of the ASBRs. It does not advertise networks outside the OSPF network; only the ASBR does that.

A

Type 4 - Summary LSA for ASBRs

69
Q

What type of LSA are originated by ASBRs in an NSSA. It is not flooded throughout the OSPF autonomous system but only to the NSSA. Similar to the Type 5 LSA.

A

Type 7 - Not-so- stubby area (NSSA) external LSA

70
Q

This LSA is produced by every router. Includes all the router’s links, interfaces, link states, and costs. This LSA type is flooded within a single area and does not travel into other areas.

A

Type 1 LSA - Router LSA

71
Q

This LSA is produced by ABRs. It is sent into an area to advertise destinations outside the area.

A

Type 3 - Summary LSA for ABRs

72
Q

What type of LSA is originated by ASBRs. Advertises destinations external to the OSPF autonomous system, flooded throughout the whole OSPF autonomous system.

A

Type 5 LSA - Autonomous system external LSA

73
Q

What type of LSAs are intra-area LSAs that have an area-flooding scope.

A

Type 1 and 2

74
Q

What type of LSAs provide reachability about the ASBR. How to get to the ASBR specifically.

A

Type 4 LSAs

75
Q

What type of LSAs are originated by ASBRs in an NSSA and are similar to the Type 5 LSA and only flooded within the NSSA?

A

Type 7 LSAs.

76
Q

What type of LSAs provide summaries of destinations outside the local area but within the OSPF domain?

A

Type 3 LSAs.

77
Q

What two types of LSAs are interarea LSAs that have an area-flooding scope.

A

Type 3 and 4

78
Q

What type of LSAs advertise external destinations and have a domain-flooding scope, which means they are flooded throughout all areas.

A

Type 5.

79
Q

T/F: Network summary LSAs (Type 3) from other areas are still flooded into a stub area.

A

True. The ABR will also send a default route to all other routers in the stub area.

80
Q

T/F: A totally stubby area sends just a single LSA for the default route.

A

True.

A totally stubby area does not flood network summary LSAs (Type 3). It stifles Type 4 LSAs, as well. Like regular stub areas, totally stubby areas do not flood Type 5 LSAs.

81
Q

T/F: Authentication in OSPF can be performed on a per-area or per-interface basis.

A

True.

OSPFv2 supports the authentication of routes using 64-bit plaintext, cryptographic Message Digest 5 (MD5), and Secure Hash (SHA) Standard authentication.

82
Q

OSPF uses IP protocol port number ______.

A

89.

83
Q

Cost is the metric used by OSPF. Which of the following is it based on?

  1. MTU
  2. Reliablilty
  3. Bandwidth
  4. Delay
  5. Load
A

Interace Bandwidth is the basis for cost.

10^8 / interface-bandwidth = cost.

84
Q

T/F: Authentication was removed from OSPFv3.

A

True.

There is no authentication in OSPFv3 directly… because OSPFv3 uses IPsec, the IPv6 authentication scheme.

85
Q

OSPFv3 retains the LSA types used by OSPFv2 with some modifications and introduces two new LSAs: link LSA and intra-area-prefix.

What is a Link LSA?

What is a Intra-area-prefix LSA?

A

Link LSA - Tells neighbors about link-local addresses and list IPv6 prefixes associated with the link

Intra-area-prefix LSA - Specifies IPv6 prefixes connected to a router, a stub network, or an associated transit network segment

86
Q

The Internet Assigned Numbers Authority (IANA) reserved TCP port ______ to identify BGP

A

179

87
Q

BGP is a ______ vector routing protocol; it is neither a distance vector nor link-state routing protocol.

A

BGP is a path vector routing protocol; it is neither a distance vector nor link-state routing protocol.

88
Q

BGP autonomous systems range from 1 through _______.

Autonomous system numbers (ASNs) 1 through ______ are considered public ASNs.

ASNs ______ through ________ are considered private ASNs.

A

BGP autonomous systems range from 1 through 65,535.

Autonomous system numbers (ASNs) 1 through 64,511 are considered public ASNs.

ASNs 64,512 through 65,535 are considered private ASNs.

89
Q

T/F: In a transit network connecting two or more AS entities and IGP can be used and is just as effective, if not better, than iBGP.

A

False.

iBGP provides a better way to control the routes within the transit autonomous system. With iBGP, the external route information (such as attributes) is forwarded.

The various IGPs that might be used do not understand or forward BGP attributes, including autonomous system paths, between eBGP routers.

90
Q

What things form a route reflector cluster?

A

The route reflector and its clients form a cluster.

All client routers in the cluster peer with the route reflectors within the cluster. The route reflectors also peer with all other route reflectors in the internetwork. A cluster can have more than one route reflector.

91
Q

What is the AD for:

  1. eBGP routes
  2. iBGP routes
A

eBGP routes: 20

iBGP routes: 200

92
Q

BGP uses ______ ___________ to select the best path to a destination.

A

BGP uses path attributes to select the best path to a destination.

93
Q

T/F: BGP attributes can be categorized as well known or optional.

A

True.

BGP attributes can be categorized as well known or optional. Well-known attributes are recognized by all BGP implementations. Optional attributes do not have to be supported by the BGP process.

94
Q

T/F: Well-known attributes can be further subcategorized as mandatory or discretionary.

A

True.

Well-known attributes can be further subcategorized as mandatory or discretionary.

  • Mandatory attributes are always included in BGP update messages.
  • Discretionary attributes might or might not be included in BGP update messages.
95
Q

T/F: BGP “optional attributes” can be further subcategorized as transitive or nontransitive.

A

True.

Optional attributes can be further subcategorized as transitive or nontransitive.

  • Routers must advertise a route with transitive attributes to their peers even if they does not support the attribute locally.
  • If the path attribute is nontransitive, the router does not have to advertise the route to its peers.
96
Q

What is the next-hop attribute?

What type is it?

  1. Well-known mandatory
  2. Well-known discretionary
  3. Optional transitive
  4. Optional non-transitive
A

The next-hop attribute is the IP address of the next IP hop that will be used to reach the destination.

The next-hop attribute is a well-known mandatory attribute.

97
Q

What is the local preference attribute?

What type of attribute is it?

  1. Well-known mandatory
  2. Well-known discretionary
  3. Optional transitive
  4. Optional non-transitive
A

The local preference attribute indicates which path to use to exit the autonomous system.

It is a well-known discretionary attribute used between iBGP peers and is not passed on to external BGP peers.

98
Q

In Cisco IOS software, the default local preference is _____. The (higher/lower?) local preference is preferred.

A

In Cisco IOS software, the default local preference is 100. The higher local preference is preferred.

99
Q

What is the origin attribute?

What type of attribute is it?

  1. Well-known mandatory
  2. Well-known discretionary
  3. Optional transitive
  4. Optional non-transitive
A

Origin is an attribute that defines the source of the path information.

Origin is a well-known mandatory attribute.

Do not confuse the origin with comparing whether a route is external (eBGP) or internal (iBGP). The origin attribute is received from the source BGP router.

100
Q

What are the three types of origin attribute?

A

Here are three types:

  1. IGP: Indicated by an i in the BGP table. Learned from an IGP
  2. EGP: Indicated by an e in the BGP table. Learned from an EGP peer.
  3. Incomplete: Indicated by a question mark (?) in the BGP table. Learned from redistribution of the route.
101
Q

When BGP is choosing a route based on origin which order are the learned routes preferred?

  • routes learned from eBGP peers
  • routes that have been verified by an IGP
  • incomplete paths
A

In terms of choosing a route based on origin, BGP prefers routes in this order:

  1. routes that have been verified by an IGP
  2. routes learned from eBGP peers
  3. incomplete paths.
102
Q

What is the AS_path attribute?

What type of attribute is it?

  1. Well-known mandatory
  2. Well-known discretionary
  3. Optional transitive
  4. Optional non-transitive
A

The AS_path, or autonomous system path, contains a list of ASNs in the path to the destination.

The AS_path is a well-known mandatory attribute.

Each autonomous system prepends its own ASN to the autonomous system path. The autonomous system path describes all the autonomous systems a packet would have to travel to reach the destination IP network.

103
Q

What is the MED attribute?

What type of attribute is it?

  1. Well-known mandatory
  2. Well-known discretionary
  3. Optional transitive
  4. Optional non-transitive
A

The multi-exit discriminator (MED) attribute tells an external BGP peer the preferred path into the autonomous system when multiple paths into the same autonomous system exist.

In other words, MED influences which one of many paths a neighboring autonomous system uses to reach destinations within the autonomous system.

It is an optional nontransitive attribute carried in eBGP updates.

104
Q

T/F: The MED attribute is not used with iBGP peers.

A

True.

The MED attribute is not used with iBGP peers.

105
Q

The (highest/lowest?) MED value is preferred, and the default value is _____. Paths received with no MED are assigned a MED of _____.

A

The lowest MED value is preferred, and the default value is 0. Paths received with no MED are assigned a MED of 0.

106
Q

See attached diagram.

Which router will RouterC choose to send traffic to? A or B?

A

With all attributes considered equal, say that Router C selects Router A as its best path into AS 100, based on Router A’s lower router ID (RID). If Router A is configured with a MED of 200, Router C will select Router B as the best path to AS 100. No additional configuration is required on Router B because the default MED is 0.

MED prefers lower values.

107
Q

What type of attribute is community?

  1. Well-known mandatory
  2. Well-known discretionary
  3. Optional transitive
  4. Optional non-transitive
A

The community attribute is an optional transitive attribute and of variable length.

108
Q

What is the weight attribute? where is it assigned? what is it used for?

What type of attribute is it?

  1. Well-known mandatory
  2. Well-known discretionary
  3. Optional transitive
  4. Optional non-transitive
  5. None of the above. Cisco proprietary
A

Weight is assigned locally on a router to specify a preferred path if multiple paths exist out of a router for a destination.

This is not propogated to non-Cisco routers because it is Cisco proprietary

109
Q

The weight value ranges from ______ to ________.

A

The weight value ranges from 0 to 65,535.

110
Q

Routes with a (lower/higher?) weight are preferred when multiple routes to a destination exist.

A

Routes with a higher weight are preferred when multiple routes to a destination exist.

111
Q

Routes that are originated by the local router have a default weight of __________.

A

Routes that are originated by the local router have a default weight of 32,768.

112
Q

The default weight for learned routes is ______.

A

The default weight for learned routes is 0.

113
Q

The BGP local preference attribute is exchanged between iBGP peers and is configured at the __________ router.

A

The BGP local preference attribute is exchanged between iBGP peers and is configured at the gateway router.

114
Q

Put the following BGP attributes in order from most to least important.

  1. Prefer local originated route
  2. Lowest MED
  3. Lowest BGP router ID source Minimum cluster list length
  4. Highest weight
  5. Highest local preference
  6. Lowest origin type
  7. Lowest neighbor address
  8. Shortest AS_Path
  9. Lowest IGP metric to the BGP next hop Oldest path
  10. Prefer eBGP over iBGP
A

“We Love Oranges AS Oranges Mean Pure Refreshment”

  1. Highest weight
  2. Highest local preference
  3. Prefer local originated route
  4. Shortest AS_Path
  5. Lowest origin type
  6. Lowest MED
  7. Prefer eBGP over iBGP
  8. Lowest IGP metric to the BGP next hop Oldest path
  9. Lowest BGP router ID source Minimum cluster list length
  10. Lowest neighbor address
115
Q

___________ between routing protocols is required to inject route information from one routing protocol to another.

A

Redistribution between routing protocols is required to inject route information from one routing protocol to another.

116
Q

BGP mnemonic for Attibutes:

“We Love Oranges AS Oranges Mean Pure Refreshment”

What is the order of the attributes?

A

“We Love Oranges AS Oranges Mean Pure Refreshment”

  1. Weight - Highest
  2. Local preference - Highest
  3. Originated route - Prefer local
  4. AS_Path - Shortest
  5. Origin type - IGP, EGP, ?(redistributed)
  6. Prefer eBGP over iBGP
  7. RID source - Lowest BGP
  8. Lowest neighbor address
117
Q

T/F: eBGP Multihop can be used to connect to a BGP neighbor across multiple hops.

A

True.

eBGP Multihop can be used to connect to a BGP neighbor across multiple hops. The BGP peering is established between the loopback addresses and not the point-to-point links. This means the BGP peers do not have to be directly connected.

119
Q

BGP Multipath Load Sharing for eBGP and iBGP allows you to configure multipath load balancing with both eBGP and iBGP paths in BGP networks.

What command is used to allow more than one path to be inserted into the BGP route table?

A

This is accomplished using the maximum-paths command.

120
Q

Routes are summarized at _______ _______ to reduce the size of routing tables.

A

Routes are summarized at network boundaries to reduce the size of routing tables.

121
Q

The recommendation for route summarization is to summarize at the _____________ layer of the network topology.

A

The recommendation for route summarization is to summarize at the distribution layer of the network topology.

122
Q

Figure 4-19 shows a hierarchical network. It has a network core, regional distribution routers, and access routes for sites.

  • All routes in Brazil are summarized with a single 10.1.0.0/16 route.
  • The North American and European routes are also summarized with 10.2.0.0/16 and 10.3.0.0/16, respectively.
  • Routers in Europe need to know only the summarized route to get to Brazil and North America and vice versa.

Where is the best place to summarize the networks?

A

The design best practice is to summarize at the distribution toward the core. The core needs to know only the summarized route of the regional areas.

123
Q

How can these class C networks be summarized?

  • 200.1.100.0
  • 200.1.101.0
  • 200.1.102.0
  • 200.1.103.0
A

In this case, you can also use summarization to aggregate four contiguous Class C networks at the /22 bit level.

For example, networks 200.1.100.0, 200.1.101.0, 200.1.102.0, and 200.1.103.0 share common bits, as shown in Table 4-9. The resulting network is 200.1.100.0/22, which you can use for a 1000-node network.

124
Q

When redistributing routes into OSPF, what command do you need to permit subenetted routes to be received?

A

When redistributing routes into OSPF, use the subnets keyword to permit subnetted routes to be received.

If you do not use it, only the major network route is redistributed, without subnetworks. In other words, OSPF performs automatic summarization to IP classful network values.

125
Q

By default, redistributed routes are classified as __________ in OSPF.

A

By default, redistributed routes are classified as external Type 2 (E2) in OSPF.

You can use the metric-type keyword to change the external route to an external Type 1 (E1).

126
Q

T/F: Using BFD can reduce failure detection even more than lowering the timers on your IGPs.

A

True.

Although reducing the EIGRP, IS-IS, and OSPF timers can result in a minimum detection timer of one to two seconds, BFD can provide failure detection in less than one second.

ENSLD 300-420 CCNP Enterprise Design (12 decks)

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