Ospf

Front 1

Default Hello and Dead timer for OSPF on a point-to-point and broadcast network.

Back 1

10 seconds and 40 seconds

Front 2

Default Hello and Dead timer for OSPF on a non-broadcast and point-to-multipoint (non) broadcast network.

Back 2

30 seconds and 120 seconds.

Front 3

Two ways to advertise a network into OSPF.

Back 3

1. Interface configuration mode:
ip ospf <process-id> area <area-#>

e.g.
R1(config)#interface serial 0/0
R1(config-if)#ip ospf 1 area 0

2. Router configuration mode:
network {ip-address | network-address} <wildcard-mask> area <area-#>

e.g.
R1(config)#router ospf 1
R1(config-router)#network 192.168.1.1 0.0.0.0 area 0

Front 4

Five OSPF Network Types and standards.

Back 4

Point-to-point (Cisco)
Broadcast (Cisco)
Point-to-multipoint nonbroadcast (Cisco)
Nonbroadcast (RFC)
Point-to-multipoint broadcast (RFC)

Front 5

A debug command use for verifying the OSPF adjacency.

Back 5

debug ip ospf adj

Note: This is also a great command to test neighbor authentications with each other.

Front 6

OSPF Authentication Types.

Back 6

Type 0 (Default: None)
Type 1 (Clear text)
Type 2 (MD5)

Front 7

OSPF authentication configuration command for all interfaces.

Back 7

An interface configuration command:
ip ospf <process-id> message-digest key <key-#> md5 <string>

And a router configuration command that enables the authentication to all interfaces:
area <area-#> authentication [message-digest]

e.g.
R1(config)#interface serial 0/0
R1(config-if)#ip ospf message-digest key 1 md5 md5-authentication

R1(config)#router ospf 1
R1(config-router)#area 0 authentication message-digest

Note: The optional [message-digest] is use for MD5 authentication (Type 2).

Front 8

OSPF interface authentication commands.

Back 8

Interface configuration commands:
ip ospf authentication [message-digest]
ip ospf authentication-key <string>
ip ospf message-digest-key <key-#> md5 <string>

Type 1 e.g.
R1(config)#interface serial 0/1
R1(config-if)#ip ospf authentication
R1(config-if)#ip ospf authentication-key clear-text-authentication

Type 2 e.g.
R1(config)#interface serial 0/0
R1(config-if)#ip ospf authentication message-digest
R1(config-if)#ip ospf message-digest-key 1 md5 md5-authentication

Note: If the all the authentication for all interfaces is enabled, the interface authentication will over write the router authentication mode.

Front 9

OSPF Neighbor Requirements.

Back 9

Unique OSPF RID
Stub area flag
Interface cannot be passive
Hello and Dead interval must match
Subnet mask must match
Must be in the same area
MTU must match
Authentication must match

Front 10

OSPF Transport layer

Back 10

Protocol type 89
It does not use UDP or TCP.

Front 11

Displays all the interfaces on which OSPF is enabled based on the "network" command (omits passive interfaces).

Back 11

show ip ospf interface brief

Front 12

Displays the contents of the (OSPF) network configuration commands for each routing process, and a list of enabled, but passive interfaces.

Back 12

show ip protocols

Front 13

Displays all summary of the OSPF database.

Back 13

show ip ospf database

Front 14

Displays all known OSPF neighbors, including the neighbor state.

Back 14

show ip ospf neighbors

Front 15

Name of the algorithm OSPF uses to calculate the best path.

Back 15

Shortest Path First (SPF)

Front 16

OSPF IPv4 multicast address for all routers and all designated routers (DR).

Back 16

224.0.0.5 (All routers)
224.0.0.6 (All DRs)

Front 17

OSPF Packet/Message Types

Back 17

Type 1 - Hello: Used to discover neighbors.
Type 2 - Database Description (DD or DBD): Used to exchange brief or summarized version of each LSA.
Type 3 - Link State Request (LSR): An LSA message which is send to neighbor to request for database/route that is needed.
Type 4 - Link State Update (LSU): A packet that contains fully detailed LSAs (group of LSAs), typically this is a response to LSR.
Type 5 - Link State Acknowledgement (LSAck): Confirmation receipt for LSU message.

Front 18

Setting OSPF Hello and Dead intervals.

Back 18

Interface configuration commands:
ip ospf hello-interval <value-in-seconds>
ip ospf dead-interval <value-in-seconds>

e.g.
R1(config)#interface serial 0/0
R1(config-if)#ip ospf hello-interval 10
R1(config-if)#ip ospf dead-interval 40

Front 19

Configuring passive interfaces.

Back 19

Router configuration commands:
passive-interface <interface> <number>
passive-interface default

e.g.
R1(config)#router ospf 1
R1(config-router)# passive-interface serial 0/0

R2(config)#router ospf 2
R2(config-router)#passive-interface default
R2(config-router)#no passive-interface serial 0/0

Note: The passive-interface default will make all the router's interfaces passive. Using the "no passive interface <interface> <number>" will disable the passive interface for specific interface.

Front 20

Configure OSPF Router ID.

Back 20

Router configuration command:
router-id <a.b.c.d>

e.g.
R1(config)#router ospf 1
R1(config-router)#router-id 1.1.1.1

Front 21

Displays the Hello and Dead timer .

Back 21

show ip ospf interface [<interface> <number>]

Front 22

Display the actual dead timer for a neighbor.

Back 22

show ip ospf neighbor [detail]

Front 23

Display the currently used OSPF authentication type and the smallest authentication type key number.

Back 23

show ip ospf interface [<interface> <number>]

Front 24

OSPF LSA Types

Back 24

Type 1 - Router: This LSA is produced by every router (This is flooded only within the originating area.)
Type 2 - Network: This LSA is produced by the DR on multi-access network (This LSA is flooded only within the originating area.)
Type 3 - Network Summary: This LSA is originated by ABR. They are sent into a single area to advertise destination outside that area.
Type 4 - ASBR Summary: This is also originated by the ABR. This LSA advertise the destination which is the ASBR. Meaning how to reach the ASBR.
Type 5 - AS External: This is originated by the ASBR. ASBR advertise the external LSA into OSPF autonomous system.
Type 6 - Group Membership: This is used in an enhancement of OSPF known as Multicast OSPF (MOSPF)-not supported by IOS.
Type 7 - NSSA External: This is originated by the ASBR within NSSA. (When an ABR receives a Type 7 LSA, the ABR will translate it to Type 5)
Type 8 - External Attributes: An alternative to running iBGP to transport BGP information across an OSPF domain. (not supported by IOS)
Type 9 - Opaque: Link-local scope
Type 10 - Opaque: Area-local scope
Type 11 - Opaque: AS-scope
(Type 9-11: Opaque is used to add various extension to OSPF, like traffic engineering parameters for MPLS networks.)

Front 25

OSPF Router Types

Back 25

Internal Routers: Routers whose all interfaces belongs to the same area.
Area Border Routers (ABR): At least one interface connected to the backbone area (Area 0) and other interface is connected to non-backbone area.
Backbone Routers: Routers that have at lease one interface connected to the backbone area. ABR is considered a Backbone Router.
Autonomous System Boundary Routers (ASBR): Gateways for external OSPF traffic (redistributed routes) from some other protocol.

Front 26

Designated Router (DR) and Backup DR (BDR) election process.

Back 26

The router with the highest interface priority will be selected as the DR. If tied on priority, the router with the highest RID will be selected as the DR.
The next highest priority or RID will be the BDR.

Front 27

Changing the OSPF interface priority.

Back 27

Interface configuration command:
ip ospf priority <priority>

e.g.
R1(config)#interface fastethernet 0/0
R1(config-if)#ip ospf priority 2

Note: The higher the priority value the chances to become the DR is higher. The default value is 1.

Front 28

OSPF Neighbor State

Back 28

Down: No Hellos have been received.

Attempt: Used when the neighbor is defined with "neighbor" command, after sending a Hello, but before receiving a Hello from that neighbor.

Init: A Hello has been received from the neighbor, but did not have the local router's RID in it, or did not pass the verification check.

2Way: A Hello has been received and the local router's RID is included.

ExStart: negotiating the DBD sequence and the Master/Slave logic used for DBD packets.

Exchange: Finished negotiating the DBD process and currently exchanging the DBD packets.

Loading: DBD packets are exchanged, and the routers area currently sending LSR, LSU and LSAck packets.

Full: Neighbors are fully adjacent.

Front 29

The LS sequence number for an LSA begins at value ___ and ends ___.

Back 29

0x80000001 to 0x7FFFFFFF

Front 30

OSPF Refresh and Flush LSA timers.

Back 30

Refresh - 30 minutes (1800 seconds)
Flush - 1 hour (3600 seconds)

Front 31

OSPF Metric formula.

Back 31

Reference Bandwidth/Interface Bandwidth

Front 32

Changing the default OSPF reference bandwidth.

Back 32

Router configuration command:
auto-cost reference-bandwidth <bandwidth-in-mbps>

R1(config)#router ospf 1
R1(config-router)#auto-cost reference-bandwidth 1000

Note: The default reference-bandwidth is 100Mbps

Front 33

Configure Type-3 LSA filtering

Back 33

Router configuration command:
area <area-id> filter-list prefix <prefix-name/number> {in | out}

Global configuration command:
ip prefix-list {name |number} {deny | permit} <ip-prefix> [{ge <prefix> | le <prefix>}]

R1(config)#ip prefix-list FILTER deny 192.168.1.0/24 le 26
R1(config)#router ospf 1
R1(config-router)#area 1 filter-list prefix FILTER out

Front 34

Filtering OSPF routes added to the routing table.

Back 34

Router configuration command:
distribute-list {prefix <name> | ACL <acl# | name> | route-map <name>} {in | out}

R1(config)#ip prefix-list FILTER 10.1.1.0/24
R1(config)#router ospf 1
R1(config-router)#distribute-prefix prefix FILTER in

Front 35

Manual summarization at ABR.

Back 35

Router configuration command:
area <area-#> range <ip-address> <mask> [cost <cost-#>]

R1(config-router)#area 1 range 10.1.2.0 255.255.254.0

Front 36

Configuring Virtual-link authentication.

Back 36

Router configuration commands:
area <transit-area-#> virtual-link <neighbor-rid> authentication message-digest
area <transit-area-#> virtual-link <neighbor-rid> message-digest-key <key-#> md5 <string>

R1config)#router ospf 1
R1(config-router)#area 1 virtual-link 3.3.3.3 authentication message-digest
R1(config-router)#area 1 virtual-link 3.3.3.3 message-digest-key 1 md5 cisco

Front 37

Default interface mode for OSPF physical interface, sub-interface multipoint and sub-interface point-to-point links.

Back 37

Physical interface and point-to-multipoint subinterface: Multipoint
Point to point subinterface: Point to point

Front 38

OSPF Interface network type that avoid the election of DR and BDR over frame-relay.

Back 38

Point to multipoint
Point to multipoint non-broadcast