Cisco Route - Ospf, Set 3

Front 1

What is the mode and command to deploy an OSPF distribute list?

Back 1

router-config mode
#distribute-list prefix <name> in [ int <name> ]

Front 2

What are two general requirements for manual summarization at an ABR?

Back 2

1. Subnet numbers in an area are in the same range
2. None of the subnets in that range exist outside the area

Front 3

What is the command and mode to configure manual route summarization at an ABR?

Back 3

router-config mode
#area <n> range <ipaddr> <net mask> [ cost n ]

Front 4

What is the IOS command to verify the OSPF cost for an interface?

Back 4

#show if ospf interface <int>

Front 5

Summarize the OSPF process to calculate the best intra-area routes

Back 5

1. Find all subnets - Type 1 and Type 2 LSAs
2. Run SPF to find all possible paths from itself to each subnet
3. Pick the route with the lowest total cost.for each subnet, based on sum of outgoing interface costs

Front 6

How does a router calculate the cost to reach an inter-area subnet?

Back 6

1. Calculate the intra area cost to the ABR
2. Add the cost in the Type-3 LSA...
This is the cost from the ABR to the destination.

Front 7

When there are both inter-area and intra-area routes to a subnet, what two rules apply?

Back 7

1. An intra-area route is always better than an inter-area route, regardless of the metric
2. If an ABR learns a TYPE-3 LSA inside a non-backbone area, the ABR ignores that LSA when calculating its own routes

Front 8

What are 6 rules for an OSPF #area <n> range command?

Back 8

1. Area number is where subnets exist
2. If subordinate subnets exist, ABR advertises summary route as Type-3 LSA
3. Does not advertise subordinate routes
4. Default metric is best metric of subordinate routes
5. Metric can be explicit with optional cost parameter
6. If no subordinates, summary not advertised...

Front 9

How do you do route filtering with the #area <n> range command?

Back 9

Use the optional non-advertise option to prevent sending Type-3 LSAs

Front 10

What is the command and mode to configure manual route summarization at an ASBR?

Back 10

router-config mode
#summary-address <prefix> <mask>
If at least one subordinate exists, advertises Type-5 LSA summary route.

Front 11

How would you use an area-range command to create a default route?

Back 11

#area 0 range 0.0.0.0 0.0.0.0 <prefix> <mask>

Front 12

What is the purpose of the default-information originate command?

Back 12

Creates a Type-5 LSA default route to flood throughout the OSPF domain.

Front 13

What is the syntax of the default-information originate command?

Back 13

#default-information originate [always] [metric <n>]
[metric-type <value>] [route-map <name>]

Front 14

What are the 5 rules for a default-information originate command?

Back 14

1. Injects Type-5 LSA only if a default route exists
2. Default metric is 1
3. Always parameter... no default route reqd
4. Metric type defines external type (2 default)
5. Route map with permit

Front 15

What is the purpose of creating OSPF stub areas?

Back 15

ABRs advertise only default routes.
Less memory and less processing of LSAs

Front 16

What are six rules for stub areas?

Back 16

1. ABRs create a Type-3 LSA for subnet 0.0.0.0
2. ABRs do not flood Type-5 LSAs
3. ABRs may not flood Type-3 LSAs
4. Default route metric 1
5. Routers in stub area do no redistribute Type-5 LSAs
6. All routers in area must be configured as stubby or neighbor relationships will fail

Front 17

What are the four types of stub areas?

Back 17

1. stub
2. totally stubby
3. NSSA
4. totally NSSA

Front 18

What is true of ALL types of stubby areas?

Back 18

Type-5 LSAs are filtered

Front 19

What is true for both types of totally stubby areas?

Back 19

Type-3 LSAs are filtered

Front 20

What is true for both types of non-totally stubby areas?

Back 20

Type-3 LSAs are advertised

Front 21

What is the difference between a stubby area and a NSSA area?

Back 21

NSSA areas allow redistribution of external routes into the area as Type-7 LSAs

Front 22

What are the commands to configure a stubby and totally stubby area?

Back 22

1. #area <id> stub -- on each router
2. add no-summary -- on ABRs

Front 23

What are the commands to verify a stubby area?

Back 23

#show ip ospf database | begin AS External
#show ip ospf database
#show ip process
#show ip ospf database database-summary
#show ip ospf

Front 24

What is the command to configure an NSSA?

Back 24

#area <n> nssa
for totally nssa, use no-summary option on ABRs

Front 25

Which feature(s) the stubby-area are Cisco proprietary?

Back 25

Both types of totally-stubby areas

Front 26

What is the purpose of an OSPF virtual-link?

Back 26

To connect a discontiguous backbone area through a non-backbone area.

Front 27

How is the virtual-link function implemented?

Back 27

Routers send the usual OSPF messages encapsulated inside unicast IP packets
Do not age (DNA) bit set. No periodic reflooding needed.

Front 28

What is the mode and command to create an OSPF virtual link?

Back 28

router-config mode
#area <n> vitual-link <router-id-of-other-end>
area number is transit area
transit area must not be stubby
cost is determined by transit-areas LSDB

Front 29

What are two commands to verify virtual links?

Back 29

#show ip ospf virtual-links
#show ip ospf neighbor detail <router-id-of-neighbor>

Front 30

What are the commands to configure no authentication and clear-text authentication over an OSPF virtual link?

Back 30

#area <n> virtual-link <router-id> authentication null
#area <n> virtual-link <router-id> authentication-ley <value>

Front 31

What are the commands to configure MD5 authtication over an OSPF virtual link?

Back 31

#area <n> virtual-link <router-id> authentication message-digest message-disgest-key <n> md5 <key-value>

Front 32

What are the commands to verify MD5 authentication for an OSPF virtual link?

Back 32

#show running-config
#show ip ospf virtual-links

Front 33

What kind of interface requires special handling for OSPF, and what are the issues?

Back 33

frame-relay multipoint interfaces have issues for:
1. Neighor discovery
2. DR/BDR

Front 34

If you have a non-broadcast multipoint frame relay network, how should neighbor relationships be defined?

Back 34

static configuration using:
#neighbor <ip> [cost <n>] [priority <n>]

Front 35

What types of frame-relay interface will not elect a DR/BDR?

Back 35

point-to-multipoint