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ICND2-Odom > OSPF/EIGRP Tune & TSHOOT > Flashcards

OSPF/EIGRP Tune & TSHOOT Flashcards

1
Q

A dynamic routing protocol is enabled on an interface. What two actions will the routing protocol immediately try to perform?

A

Attempt to find suitable neighbor on connected subnet, attempt to advertise the subnet connected to that interface

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2
Q

Describe a router’s behavior when passive-interface is configured on an interface

A

Router will not attempt to find neighbors off that interface (stop sending/processing hellos), but will continue to advertise that interface’s subnet.

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3
Q

What command will list interfaces on which EIGRP is enabled? Will the output of that command list or identify passive interfaces?

A

show ip eigrp interfaces — no

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4
Q

What command will list interfaces on which OSPFv2 is enabled? Will the output of that command list or identify passive interfaces?

A

show ip ospf interface brief – passive interfaces are listed, but not explicitly identified as passive

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5
Q

What command implicitly reveals configuration of a dynamic routing protocols, including passive interfaces

A

show ip protocols

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6
Q

From an L1,L2,L3 perspective, what must be true for EIGRP or OSPf to successfully form neighbor relationships?

A

Interfaces must be up/up, must be on same subnet, ACLs must not be filtering RP messages

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7
Q

What are the neighborship requirements for EIGRP?

A

Must be on same subnet
Must use same ASN
Must use same k-values
Must pass authentication, if configured

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8
Q

Two EIGRP routers are expected to form a neighbor relationship. You suspect they might not be on the same subnet. What commands should be used to verify this?

A

show interfaces, show ip interfaces

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9
Q

Two EIGRP routers are expected to form a neighbor relationship. You suspect they might not be configured for the same ASN. What commands should be used to verify this?

A

show ip eigrp interfaces, show ip protocols

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10
Q

Two EIGRP routers are expected to form a neighbor relationship. You suspect they might not be using the same K-values. What commands should be used to verify this?

A

show ip protocols

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11
Q

Two EIGRP routers are expected to form a neighbor relationship. You suspect that authentication issues may be present. What commands should be used to verify this?

A

debug eigrp packets

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12
Q

What re the neighborship requirements for OSPF?

A 
Must be on same subnet
Must pass authentication, if configured
RIDs must be unique
Must be in same area
Hello-interval and dead-interval must match
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13
Q

Two OSPF routers are expected to form a neighbor relationship. You suspect they may not be in the same subnet. What commands should be used to verify this?

A

show interfaces, debug ip ospf hello

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14
Q

Two OSPF routers are expected to form a neighbor relationship. You suspect their RIDs might not be unique. What commands should be used to verify this?

A

show ip ospf interface, debug ip ospf adj

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15
Q

Two OSPF routers are expected to form a neighbor relationship. You suspect they may not be in the same area. What commands should be used to verify this?

A

show ip ospf interface brief, debug ip ospf adj

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16
Q

Two OSPF routers are expected to form a neighbor relationship. You suspect a hold-interval or dead-interval mismatch. What commands should be used to verify this?

A

show ip ospf interface, debug ip ospf hello

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17
Q

Two OSPF routers. have different process IDs. Can they become neighbors?

A

Yes. Process IDs do not have to match for OSPF

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18
Q

Two EIGRP routers have different hello-intervals or hold-times. Can they become neighbors?

A

Yes. Timers do not have to match for EIGRP

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19
Q

OSPF is configured on a router as follows:

network 1.0.0.0 0.0.0.255 area 1
network 1.1.1.1 0.0.0.0 area 0

Which network will OSPF advertise?

A

OSPF will advertise network 1.0.0.0/24 as area 1. OSPF uses the first network statement that can be matched.

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20
Q

OSPF is configured on a router with a network statement matching an interface in area 0. That same interface includes a configuration statement:

ip ospf 1 area 2

Which configuration will end up being used?

A

The interface configuration takes precedence

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21
Q

An EIGRP or OSPF router shows evidence of full and correct configuration, but is not forming neighbor relationships. What might this indicate?

A

Indicates the routing process may have been configured with the shutdown command

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22
Q

Two OSPF routers are not forming the expected neighbor relationship. Inspection reveals that one interface has the following configuration:

ip mtu 1492

The other router’s interface on that subnet has no similar configuration. Explain how to determine what that interface’s MTU might be, and why this causes a neighborship problem

A

show ip interfaces int-id

If MTU mismatch, both routers will attempt to form a neighbor relationship, but will fail to exchange LSDBs. Eventually, the neighbor relationship fails.

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23
Q

IF EIGRP is configured with auto-summart, where does EIGRP perform the summarization?

A

at classful boundaries

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24
Q

What command is used to determine whether EIGRP is performing auto-summarization?

A

show ip protocols

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25
Q

If EIGRP is performing auto-summarization, one what interfaces will summarized updates be sent

A

Only via interfaces on different major classful networks

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26
Q

R1 is using EIGRP to advertise a summary route of 172.16.0.0/16, but is actually only connected to 172.16.1.0/24, 172.16.2.0/24, and 172.16.4.0/24. How would EIGRP respond to incoming packets for 172.16.3.0/24?

A

EIGRP would create a summary route to null0 for 172.16.0.0/16. Packets to 172.16.3.0/24 would be routed to null0 (and thus dropped).

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27
Q

Under what conditions does EIGRP include a null0 summary route?

A

Auto-summary is enabled
At least one subnet was learned by EIGRP
At least 2 network EIGRP commands are configured

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28
Q

What is the purpose of a null0 summary route

A

loop prevention

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29
Q

Under EIGRP, what command is used to propagate a default route?

A

redistribute static router subcommand

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30
Q

What is the administrative distance of an external EIGRP route, such as a propagated default route?

A

170

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31
Q

By default, what percentage of an interface’s bandwidth will EIGRP attempt to use for for EIGRP information?

A

50 percent

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32
Q

On an interface with low bandwidth, you suspect that EIGRP overhead is interfering with throughput. What command should be used to throttle EIGRP traffic on that interface so that only 30 percent of the interface’s bandwidth is used? Assume the AS number for the eigrp process is 209

A

ip bandwidth-percent eigrp 209 30

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33
Q

How often will EIGRP Hello messages be sent by default on links low-speed NBMA networks?

A

every 60 seconds

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34
Q

By default, how long will an EIGRP router wait to receive hello messages before declaring it’s neighbor router dead on low-speed NBMA networks

A

180 seconds (3x hello-interval)

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35
Q

How often will EIGRP Hello messages be sent by default on links with bandwidth > 1.544 Mbps?

A

Every 5 seconds

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36
Q

By default, how long will an EIGRP router wait to receive hello messages before declaring it’s neighbor router dead on > 1.544 Mbps

A

15 seconds (3x hello-interval)

37
Q

Two EIGRP routers are configured with different hello-intervals and hold-times. Will they form an adjacency?

A

Yes, those intervals do not have to match, but they should, as the link will probably flap

38
Q

What command is used on an interface to set the frequency of hello message transmission on a router running EIGRP?

A

ip hello-interval eigrp $asn $seconds

39
Q

What command is used on an interface to tell a neighbor router how long to wait for hello message on a router running EIGRP?

A

ip hold-time eigrp $asn $seconds

40
Q

When considering equal-cost load balancing with EIGRP, how many equal-cost paths will EIGRP use by default. How would this be adjusted? How would this change be verified?

A

4 by default. Adjust with maximum-paths router subcommand. Verify via show ip protocols (lists max-paths)

41
Q

When considering unequal cost load balancing with EIGRP, describe when it might be used. How would it be accomplished?

A

used when metrics are different, but close. Accomplished with variance $multiplier router subcommand.

42
Q

What are some key considerations about the variance command?

A

Variance is multiplied by feasible distance

Assuming max-paths allows more routes, any FS routes with metrics < variance product are added to the routing table as balanced

Routes that are not successors or FS can never be added to the routing table, regardless of the variance

43
Q

When troubleshooting EIGRP neighbor issues, what are conditions that should be checked?

A 
Are interfaces operational?
Are interfaces enabled for EIGRP?
Same ASN?
Same K-values?
Passive interfaces?
44
Q

When troubleshooting EIGRP routing table issues, what are conditions that should be checked?

A

Passive-interfaces?
Auto-Summary?
Missing network statements?

45
Q

What formula is used to calculate the number of potential adjancnies is an OSPF network

A

[n(n-1)]/2

46
Q

How many adjacencies are potentially possible in an OSPF network with 10 routers?

A

45

47
Q

What is the purpose of the OSPF DR?

A

Collection and distribution point for LSAs

48
Q

What address do DROTHER routers send their LSAs to when using OSPFv2?

A

224.0.0.6 (all DR)

49
Q

What address to DR routers send their LSAs to when using OSPFv2?

A

224.0.0.5 (all OSPF)

50
Q

What is the role of the BDR?

A

Listen passively for LSAs. Promote self to DR if DR stops responding to hellos

51
Q

To what routers will DROTHER routers form full adjacencies?

A

DR and BDR

52
Q

You want to quickly verify which routers are acting as DR and BDR in a working OSPFv2 network. What command will immediately reveal this information?

A

show ip ospf int $int-id on a working OSPF interface will reveal this routers role, as well as the DR (by RID and interface address) and BDR (by RID and interface address)

53
Q

What determines the outcome of an OSPF DR/DBR election

A
  1. Highest interface priority

2. Highest RID

54
Q

Two OSPF routers have equal interface priorities, but different RIDs. Which becomes DR?

A

The router with the highest RID

55
Q

Multiple routers are operating in an OSPF network. All are configured with the same interface priority. A new router is introduced with a higher interface priority. Will that trigger an election?

A

No. Elections are not preemptive

56
Q

What will trigger an OSPF election?

A

DR failure
OSPF process restart
Multi-access interface goes down

57
Q

What happens during an OSPF election?

A

BDR immediately becomes DR. Other routers on the shared link will attempt to become new BDR. Router with the highest interface priority will become BDR. If all interface priorities are equal, router with the highest RID will become BDR.

58
Q

Is it better to influence the DR election process by interface priority or RID?

A

Interface priority preferred

59
Q

What command is used to configure OSPF interface priority on a given interface?

A

ip ospf priority $value

$value=0-255

60
Q

What is the default OSPF interface priority?

A

1

61
Q

An interface is configured with ip ospf priority 0. What does that imply?

A

The router will never attempt to become DR or BDR

62
Q

What is the default interface priority on a serial link?

A
  1. NBMA networks don’t require a DBR or BDR
63
Q

An OSPF network has been working correctly for some time. A decision is made to change interface priority on certain devices to influence future DR/BDR elections. After the priorities are changed, what action should be taken immediately?

A

OSPF process on all routers should be restarted to force a new election

64
Q

How is a default route propagated when using OSPF

A

default-information originate router subcommand

65
Q

You notice a default route on an OSPF router listed as O*E1. What does that imply?

A

Cost to reach default route includes both external and internal cost.

66
Q

You notice a default route on an OSPF router listed as O*E2. What does that imply?

A

Cost to reach external route only includes external cost

67
Q

When two OSPF routers are attempting to become neighbors, is it a requirement that their hello-interval and dead-intervals match?

A

Yes

68
Q

What is the default hello interval for OSPF

A

10 sec

69
Q

What is the default dead interval for OSPF?

A

40 sec (4x hello)

70
Q

How would one verify the current hello or dead intervals on a given interface?

A

show ip ospf interface $int-id

71
Q

How would one change the frequency of hellos sent on a given OSPF-enabled interface?

A

per interface:

ip ospf hello-interval $sec

72
Q

How would one change how long an OSPF router should wait to receive hellos before declaring its neighbor dead?

A

ip ospf dead-interval $sec

73
Q

What OSPF states are related to adjacency formation?

A

Down/Init/2-Way

74
Q

What OSPF states are related to database synchronization

A

ExStart/Exchange/Loading/Full

75
Q

Describe the OSPF Down state

A

No Hellos received yet
Router sends hello
Transition to INIT

76
Q

Describe the OSPF Init state

A

Hello rec’d
Sending router’s RID noticed
Transition to 2-WAY

77
Q

Describe the OSPF 2-Way state

A

DR/BDR election on multiaccess networks

Transition to EXSTART

78
Q

Describe the OSPF ExStart state

A

Master/slave negotiation
DBD sequence determination
Master initiates EXCHANGE

79
Q

Describe the OSPF Exchange state

A

Routers exchange DBD packets

*decsion:
if more information about routes needed, transition to LOADING. Otherwise transition to FULL

80
Q

Describe the OSPF LOADING state

A

Exchange of LSRs and LSUs
Possible routes processed with SPF
Routes added to routing table
Transition to FULL

81
Q

Describe the OSPF Full state

A

routers have reached convergence

82
Q

When troubleshooting OSPF neighbor issues, what conditions should be checked?

A 
Interfaces operational?
Same subnet?
Interfaces enable fo OSPF?
Unique RIDs?
OSPF areas match?
Passive interfaces?
83
Q

When troubleshooting OSPF neighbor issues, what conditions should be checked?

A

Are networks advertised?
ACL blocking?
Another RP with lower AD?
All areas connected to area 0?

84
Q

When troubleshooting OSPF path selection issues, what conditions should be checked?

A

verify interface cost

verify ospf reference bandwidth

85
Q

What is contained in the OSPF interface table

A

list of enabled interfaces

type 1 LSAs, including subnets

86
Q

Describe the OSPF neighbor table

A

Maintains adjacencies via hello/dead timers
Entries added/refreshed when hellos received
Entires removed when dead timer expires

87
Q

Describe the purpose of the OSPF LSDB

A

Stores full topology information

88
Q

Describe how OSPF routes are added to the routing table.

A

After SPF calculation, best routes are offered to the routing table.

ICND2-Odom (7 decks)

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