Cisco Route - Ospf, Set 2

Front 1

What information is stored in an OSPF link-state database?

Back 1

1. The existence of and identifier for each router (router-id)
2. Each router interface, ip address, mask, subnet
3. List of routers reachable by each router on each interface

Front 2

If an interface matches more than one OSPF network command, which one applies?

Back 2

1. OSPF orders network commands by most-specific first
2. The first network command that matches the interface used

Front 3

What are six commands used to verify OSPF?

Back 3

#show ip ospf
#show ip ospf interface brief (shows area #)
#show ip ospf neighbors
#show ip ospf database
#show ip protocols
#show ip route

Front 4

What IP addresses does OSPF use to send updates?

Back 4

1. 224.0.0.5 (all OSPF routers)
2. 224.0.0.6 (all DRs)

Front 5

Does OSPF send full or partial topology updates?

Back 5

Full updates when neighbors are discovered; partial after.

Front 6

What are the two requirements for OSPF to send hello messages on an interface?

Back 6

1. OSPF enabled on interface by #network command or #ip ospf area command
2. Interface not been made passive

Front 7

How do you enable OSPF hellos directly on an interface?

Back 7

interface mode
#ip ospf <process> area <n>

Front 8

What are seven requirements for OSPF routers to become neighbors?

Back 8

1. Primary IP addresses in same subnet, same mask.
2. Interface not passive
3. Must be in same area
4. Hello and dead timers match
5. Unique router-ids
6. IP MTU must match
7. Authentication successful

Front 9

What IOS command would you use to see which interfaces are active and passive?

Back 9

#show ip protocols

Front 10

What are the IOS commands used to set the OSPF hello-timer and dead timer?

Back 10

interface mode
#ip ospf hello-interval <n>
#ip ospf dead-interval <n>

Front 11

What IOS commands show the state of a neighbor relationship?
What are the possible states?

Back 11

#show ip ospf neighbors [brief]
1. down
2. init
3. seen
4. 2Way - neighbors, but no direct topo exchange.
5. Full/DR or Full/BDR

Front 12

What is the OSPF minimal-hello multiplier? What is the command to deploy it?

Back 12

sets dead interval = 1 s
hello interval = 1/n
#ip ospf dead-interval minimal hello-multiplier <n>

Front 13

How do you set the MTU for an interface? (2 commands)

Back 13

#ip mtu <x> (just for IP)
#mtu <x> (all layer 3 protocols)

Front 14

What are the commands and mode to enable OSPF clear-text authentication?

Back 14

interface mode
#ip ospf authentication
#ip ospf authentication-key <value>

Front 15

What are the commands and mode to enable OSPF md5 authentication?

Back 15

interface mode
#ip ospf authentication message-digest
#ip ospf message-digest-key <number> md5 <key-value>

Front 16

What is the IOS command to verify OSPF authentication?

Back 16

#debug ip ospf adjacency

Front 17

What is the mode and command to override the default OSPF authentication?
What is the advantage of this?

Back 17

router-config mode
#area <x> authentication [message-digest]
advantage: if you do this, you don't need to set the authentication on every interface.

Front 18

What is the OSPF command to verify authentication setup for an interface?

Back 18

#show ip ospf interface <interface>

Front 19

How do you migrate to a new key when using OSPF authentication?

Back 19

Configure the new key value on all routers in a subnet, then delete the configuration for the old keys.

Front 20

How do you set the OSPF network type on an interface, and what are the possible settings?

Back 20

#ip ospf network <type>
1. broadcast
2. point-to-point
3. nonbroadcast (NBMA)
4. point-to-multipoint
5. point-to-multipoint nonbroadcast

Front 21

OSPF: Which interface network types use a DR/BDR?

Back 21

Only Broadast and NBMA

Front 22

What is the default OSPF hello timer by interface type?

Back 22

10 seconds for broadcast and point-to-point
30 seconds for all others

Front 23

Which interface network types support dynamic discovery of OSPF neighbors?

Back 23

Broadcast, point-to-point, and point-to-multipoint

Front 24

Which interface types allow more than two OSPF routers on a subnet?

Back 24

Broadcast, NBMA, point-to-multipoint, and point-to-multipoint nonbroadcast

Front 25

What is the default network interface type for frame relay point-to-point subinterfaces?

Back 25

Point-to-point

Front 26

What is the default network interface type for frame relay physical and multipoint subinterfaces?

Back 26

NBMA

Front 27

What ios command shows the interface network type?

Back 27

#show ip ospf interface <interface>

Front 28

What are the two responsibilities of an OSPF DR?

Back 28

1. Create and flood Type-2 network LSAs for the subnet
2. Aid in database exchange over the subnet

Front 29

What are the commands to verify OSPF links

Back 29

#show ip ospf database
#show ip ospf database router <r-id>
#show ip ospf database network <ip>
#show ip ospf database summary <network>

Front 30

What command can be used to protect an OSPF router from learning too many LSAs?

Back 30

router ospf mode
#max-lsa <n>
Logs events. Eventually discards LSDB and starts over based on ignore-time and number of times to ignore event.
Both configured using #max-lsa

Front 31

What kinds of route filtering does OSPF allow and not allow?

Back 31

Intra-area filtering (Type-1 and Type-2 LSAs) cannot be filtered.
Inter-area routing is allowed.
Type-3 LSAs on ABRs
Type-5 LSAs on ASBRs

Front 32

What is the mode and command to configure OSPF LSA Type-3 filtering?

Back 32

#router ospf
#area <n> filter-list prefix <name> { in | out }

Front 33

Give an example of a prefix list that would filter all routes to network 10.5.6.0/24 from coming into area 5

Back 33

#ip prefix-list filter-into-5 seq 10 deny 10.5.6.0/24
#ip prefix-list filter-into-5 seq 20 permit 0.0.0.0/0 le 32
#router ospf <n>
#area 5 filter-list prefix filter-into-5 in

Front 34

If you want to filter a route so that some of the routers in an OSPF area do not learn the route, what type of filtering will you use?

Back 34

Filter using distribution lists.
Type-3 filtering will not work (prefix-lists) because that will filter an LSA from an entire area.

Front 35

Describe four rules for using a distribute list to filter routes in OSPF.

Back 35

1. in or out required, but only in works
2. Refer to a numbered ACL, a named ACL, prefix list, or route-map.
3. Permit allows route, deny filters
4. Optioanl interface <name> parameter compares with outgoing interface

Front 36

Which OSPF LSAs are flooded only within an area and not between areas?

Back 36

LSA Types 1, 2, 4, and 7.

Front 37

What is the hello-dead interval process between two routers on a virtual link? What is the DR/BDR process for the same scenario?

Back 37

There is no hello-dead time process for a virtual link
There is no DR/BDR process for a virtual link