OSPF

Question 1

Type 1 Router LSA

Answer 1

Contains IP prefix of each connected interface

Stays in an area

Question 2

Type 2 Network LSA

Answer 2

Generated by DR

A DR collects Type 1 LSA from other OSPF routers on a broadcast segment and combines them into a type 2 LSA that describes all routers on the segment

Stays in an area

Question 3

Type 3 Summary LSA

Answer 3

Includes inter-area prefixes-prefixes from other areas.

Summarizes Type 1 and 2 LSA from an area and repackage them into a single summary LSA to share with other areas

O IA in the routing table

Stays in an area

Question 4

Type 4 ASBR Summary LSA

Answer 4

Generated by an ABR and tells routers in other areas how to reach the next hop listed in type 5 AS External LSA

Stays in an area

Question 5

Type 5 AS External LSA

Answer 5

Advertises redistributed routes

OE1 and OE2 in the routing table.

Flooded to all normal area

Question 6

OSPF Network Types

Answer 6

Point-to-point: Routers will not attempt to elect a DR
Used for serial links and loopbacks

Broadcast or Transit: Routers will attempt to elect a DR
Most common on ethernet networks

Question 7

OSPF Routing Protocol Number

Answer 7

OSPF uses IP protocol 89

Question 8

OSPF Multicast Address

Answer 8

OSPF routers use 224.0.0.5 to send HELLO messages

On a Broadcast network, The DR multicast address is 224.0.0.6

Question 9

OSPF Seven States

Answer 9

1. Down
2. Init
3. Two-way
4. Exstart
5. Exchange - Routers exchange LSA headers
6. Loading - Routers exchange full link-state
7. Full

Question 10

Changing Interface Priority

Answer 10

By default, all routers have an interface priority of 1.

R2(config-if)# ip ospf priority 255

If a router has a priority of 0 it will never become a DR

Question 11

OSPF Stub Network

Answer 11

Contains only a single router. Advertise using a type 2 LSA

Question 12

OSPF Authentication Types

Answer 12

Interface Authentication: Each router must authenticate to its neighbor before forming an adjacency

R2(config-if)# ip ospf message-digest-key 1 md5 cisco
ip ospf authentication message-digest

Area Authentication: Enables interface authentication on all interfaces in a particular area.

R2(config-if)# ip ospf message-digest-key 1 md5 cisco

R2(config-router)# router ospf 1
area 0 authentication message-digest

Question 13

Passive Interfaces

Answer 13

OSPF will advertise a prefix for an interface but will not form an adjacency

R2(config-router)# router ospf 1
passive-interface gi0/1

Question 14

Inter-Area Summarization

Answer 14

On ABR area range command
On ASBR summary-address command

R2(config-router)# router ospf 1
area 0 range 10.0.0.0 255.255.254.0

Question 15

Route Filtering

Answer 15

Inter-area filtering mechanism. Router will not advertise a summary LSA

R4(config)# ip prefix-list NO-AREA-1 seq 10 deny 192.0.2.0/30
ip prefix-list NO-AREA-1 seq 20 permit 0.0.0.0/0 le 32

R4(config-router)# router ospf 1
area 0 filter-list prefix NO-AREA-1 in

Question 16

Distribute Lists

Answer 16

Prevents a prefix from entering into the routing table but still present in the OSPF LSA

R4(config)# ip access-list standard R2_LO
deny host 2.2.2.2
permit any

R4(config-router)# router ospf 1
distribute-list R2_LO in