Configuring OSPF Network Types

There are multiple OSPF Network Types that can be configured to directly affect the operation of OSPF on a specific interface. This lab will discuss and demonstrate the configuration and verification of the different OSPF Network Types.

Real World Application & Core Knowledge

When building out an OSPF network you must take into consideration of the internet network types. This is dependent on the layer 2 technology used such as Ethernet, point-to-point T1 circuit, frame relay and even frame relay with no broadcast.

There are five different configurable OSPF network types on a Cisco router, broadcast, non-broadcast, point-to-point, point-to-multipoint and point-to-multipoint non-broadcast.

As a network engineer in the field working with OSPF you must know the differences in the OSPF network types and which types are compatible with one another. Some types will work with each other but you have to adjust the hello/dead timers. With this being said the following list below shows which OSPF network types can inter-operate with each other;

Broadcast to Broadcast
Non-broadcast to Non-broadcast
Point-to-Point to Point-to-Point
Broadcast to Non-broadcast (adjust hello/dead timers)
Point-to-Point to Point-to-Multipoint (adjust hello/head timers)

If you’ve read through Lab 9-1 you’ll see a nice little bullet list of the different types of OSPF network types and their features, I’ve added that list to this lab to refresh your memory. As a CCNA you must know these network types inside and out;

Non-Broadcast

The Non-Broadcast network type is the default for OSPF enabled frame relay physical interfaces.
Non-Broadcast networks requires the configuration of static neighbors; hello’s are sent via unicast.
The Non-Broadcast network type has a 30 second hello and 120 second dead timer.
An OSPF Non-Broadcast network type requires the use of a DR/BDR

Broadcast

The Broadcast network type is the default for an OSPF enabled ethernet interface.
The Broadcast network type requires that a link support Layer 2 Broadcast capabilities.
The Broadcast network type has a 10 second hello and 40 second dead timer.
An OSPF Broadcast network type requires the use of a DR/BDR.

Point-to-Point

A Point-to-Point OSPF network type does not maintain a DR/BDR relationship.
The Point-to-Point network type has a 10 second hello and 40 second dead timer.
Point-to-Point network types are intended to be used between 2 directly connected routers.

Point-to-Multipoint

OSPF treats Point-to-Multipoint networks as a collective of point-to-point links.
Point-to-Multipoint networks do not maintain a DR/BDR relationship.
Point-to-Multipoint networks advertise a hot route for all the frame-relay endpoints.
The Point-to-Multipoint network type has a 30 second hello and 120 second dead timer.

Point-to-Multipoint Non-Broadcast

Same as Point-to-Multipoint but requires static neighbors. Used on Non-broadcast layer 2 topologies.
Gives you the ability to define link cost on a per neighbor basis.

Loopback

The default OSPF network type; only available to loopback interfaces.
Advertises the interface as a host route; changeable by configuring the interface as point-to-point.

While mixing and matching the different OSPF network types may be required some some scenarios; it is however outside of the scope of the CCNA objectives. This lab is just to demonstrate how to configure the different OSPF network types.

In this lab you will configure the interfaces of R1, R2, R4 and R5 as an OSPF point-to-multipoint network type and verify the configuration.

Familiarize yourself with the following new command(s);

Command	Description
ip ospf network networktype	This command is executed in interface configuration mode and configures the OSPF network type on a per interface basis.
show ip ospf interface interface#/#	This command is executed in privileged mode and displays interface parameters relating to OSPF configuration such as network type and hello/dead timers.

The following logical topology shown below is used in labs found through out Section 9 – Configuring OSPF;

Lab Prerequisites

If you are using GNS3 than load the Free CCNA Workbook GNS3 topology than start devices; R1, R2, R3, R4, R5 and SW1.
Establish a console session with devices R1, R2, R3, R4, R5 and SW1 than load the initial configurations provided below by copying the config from the textbox and pasting it into the respected routers console.

!################################################## !# Free CCNA Workbook Lab 9-3 R1 Initial Config # !################################################## ! enable configure terminal ! hostname R1 no ip domain-lookup ! interface Loopback0 description ### SIMULATED NETWORK ### ip address 10.90.10.1 255.255.255.0 ! interface Serial0/0 description ### PHYSICAL FRAME RELAY INTERFACE ### ip address 10.90.245.1 255.255.255.248 ip ospf network broadcast encapsulation frame-relay serial restart-delay 0 frame-relay map ip 10.90.245.5 125 broadcast frame-relay map ip 10.90.245.4 124 broadcast frame-relay map ip 10.90.245.2 122 broadcast no frame-relay inverse-arp no shut exit ! router ospf 1 log-adjacency-changes network 10.90.245.1 0.0.0.0 area 0 ! line con 0 logging sync no exec-timeout ! end !################################################## !# Free CCNA Workbook Lab 9-3 R2 Initial Config # !################################################## ! enable configure terminal ! hostname R2 no ip domain-lookup ! interface Loopback0 description ### SIMULATED NETWORK ### ip address 10.90.20.1 255.255.255.0 ! interface Serial0/0 description ### PHYSICAL FRAME RELAY INTERFACE ### ip address 10.90.245.2 255.255.255.248 encapsulation frame-relay ip ospf network broadcast ip ospf priority 0 serial restart-delay 0 no frame-relay inverse-arp frame map ip 10.90.245.1 221 broadcast frame map ip 10.90.245.4 221 frame map ip 10.90.245.5 221 no shut ! interface Serial0/2 ### POINT-TO-POINT LINK TO R3 ### ip address 10.90.23.1 255.255.255.252 encapsulation ppp serial restart-delay 0 no shut exit ! router ospf 1 log-adjacency-changes network 10.90.245.2 0.0.0.0 area 0 ! line con 0 logging sync no exec-timeout ! end !################################################## !# Free CCNA Workbook Lab 9-3 R3 Initial Config # !################################################## ! enable configure terminal ! hostname R3 no ip domain-lookup ! interface Loopback0 description ### SIMULATED NETWORK ### ip address 10.90.30.1 255.255.255.0 ! interface Serial0/1 description ### POINT-TO-POINT LINK TO R2 ### ip address 10.90.23.2 255.255.255.252 encapsulation ppp no shut exit ! line con 0 logging sync no exec-timeout ! end !################################################## !# Free CCNA Workbook Lab 9-3 R4 Initial Config # !################################################## ! enable configure terminal ! hostname R4 no ip domain-lookup ! interface Loopback0 description ### SIMULATED NETWORK ### ip address 10.90.40.1 255.255.255.0 ! interface FastEthernet0/0 description ### REAL NETWORK ### ip address 10.90.145.1 255.255.255.0 no shut ! interface Serial0/0 description ### PHYSICAL FRAME RELAY INTERFACE ### ip address 10.90.245.4 255.255.255.248 encapsulation frame-relay ip ospf network broadcast ip ospf priority 0 serial restart-delay 0 no frame-relay inverse-arp frame map ip 10.90.245.1 421 broadcast frame map ip 10.90.245.2 421 frame map ip 10.90.245.5 421 no shut ! interface Serial0/1 description ### POINT-TO-POINT LINK TO R5 ### ip address 10.90.45.1 255.255.255.252 encapsulation ppp serial restart-delay 0 no shut exit ! router ospf 1 log-adjacency-changes network 10.90.245.4 0.0.0.0 area 0 ! line con 0 logging sync no exec-timeout ! end !################################################## !# Free CCNA Workbook Lab 9-3 R5 Initial Config # !################################################## ! enable configure terminal ! hostname R5 no ip domain-lookup ! interface Loopback0 description ### SIMULATED NETWORK ### ip address 10.90.50.1 255.255.255.0 ! interface FastEthernet0/0 description ### REAL NETWORK ### ip address 10.90.145.2 255.255.255.0 no shut ! interface Serial0/0 description ### PHYSICAL FRAME RELAY INTERFACE ### ip address 10.90.245.5 255.255.255.248 encapsulation frame-relay ip ospf network broadcast ip ospf priority 0 serial restart-delay 0 no frame-relay inverse-arp frame map ip 10.90.245.1 521 broadcast frame map ip 10.90.245.2 521 frame map ip 10.90.245.4 521 no shut ! interface Serial0/1 description ### POINT-TO-POINT LINK TO R4 ### ip address 10.90.45.2 255.255.255.252 encapsulation ppp serial restart-delay 0 no shut exit ! router ospf 1 log-adjacency-changes network 10.90.245.5 0.0.0.0 area 0 ! line con 0 logging sync no exec-timeout ! end !################################################## !# Free CCNA Workbook Lab 9-3 SW1 Initial Config # !################################################## ! enable configure terminal ! hostname SW1 no ip domain-lookup ! line con 0 logging sync no exec-timeout ! end

Lab Objectives

Configure the Serial interfaces connecting R1, R2, R4 and R5 to the hub-and-spoke frame relay topology as an OSPF point-to-multipoint network type.
Verify the network type configuration change by viewing the OSPF parameters of the serial interface.
Verify the neighbor relationships on R1 by viewing the neighbor table.

Lab Instruction

Objective 1. – Configure the Serial interfaces connecting R1, R2, R4 and R5 to the hub-and-spoke frame relay topology as an OSPF point-to-multipoint network type.

R1>enable
R1#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
R1(config)#interface Serial0/0
R1(config-if)#ip ospf network point-to-multipoint
R1(config-if)#end
R1#
%OSPF-5-ADJCHG: Process 1, Nbr 10.90.20.1 on Serial0/0 from FULL to DOWN, Neighbor Down: Interface down or detached
%OSPF-5-ADJCHG: Process 1, Nbr 10.90.40.1 on Serial0/0 from FULL to DOWN, Neighbor Down: Interface down or detached
%OSPF-5-ADJCHG: Process 1, Nbr 10.90.50.1 on Serial0/0 from FULL to DOWN, Neighbor Down: Interface down or detached
%SYS-5-CONFIG_I: Configured from console by console
R1#

%OSPF-5-ADJCHG: Process 1, Nbr 10.90.10.1 on Serial0/0 from FULL to DOWN, Neighbor Down: Dead timer expired
R2>enable
R2#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
R2(config)#interface Serial0/0
R2(config-if)#ip ospf network point-to-multipoint
R2(config-if)#end
R2#
%SYS-5-CONFIG_I: Configured from console by console
%OSPF-5-ADJCHG: Process 1, Nbr 10.90.10.1 on Serial0/0 from LOADING to FULL, Loading Done
R2#

%OSPF-5-ADJCHG: Process 1, Nbr 10.90.10.1 on Serial0/0 from FULL to DOWN, Neighbor Down: Dead timer expired
R4>enable
R4#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
R4(config)#interface Serial0/0
R4(config-if)#ip ospf network point-to-multipoint
R4(config-if)#end
R4#
%SYS-5-CONFIG_I: Configured from console by console
%OSPF-5-ADJCHG: Process 1, Nbr 10.90.10.1 on Serial0/0 from LOADING to FULL, Loading Done
R4#

%OSPF-5-ADJCHG: Process 1, Nbr 10.90.10.1 on Serial0/0 from FULL to DOWN, Neighbor Down: Dead timer expired
R5>enable
R5#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
R5(config)#interface Serial0/0
R5(config-if)#ip ospf network point-to-multipoint
R5(config-if)#end
R5#
%SYS-5-CONFIG_I: Configured from console by console
%OSPF-5-ADJCHG: Process 1, Nbr 10.90.10.1 on Serial0/0 from LOADING to FULL, Loading Done
R5#

Objective 2. – Verify the network type configuration change by viewing the OSPF parameters of the serial interface.

R1#show ip ospf interface Serial0/0
Serial0/0 is up, line protocol is up 
  Internet Address 10.90.245.1/29, Area 0 
  Process ID 1, Router ID 10.90.10.1, Network Type POINT_TO_MULTIPOINT,
Cost: 64
  Transmit Delay is 1 sec, State POINT_TO_MULTIPOINT
  Timer intervals configured, Hello 30, Dead 120, Wait 120, Retransmit 5
    oob-resync timeout 120
    Hello due in 00:00:02
  Supports Link-local Signaling (LLS)
  Cisco NSF helper support enabled
  IETF NSF helper support enabled
  Index 1/1, flood queue length 0
  Next 0x0(0)/0x0(0)
  Last flood scan length is 1, maximum is 3
  Last flood scan time is 4 msec, maximum is 4 msec
  Neighbor Count is 3, Adjacent neighbor count is 3 
    Adjacent with neighbor 10.90.50.1
    Adjacent with neighbor 10.90.40.1
    Adjacent with neighbor 10.90.20.1
  Suppress hello for 0 neighbor(s)
R1#

R2#show ip ospf interface Serial0/0
Serial0/0 is up, line protocol is up 
  Internet Address 10.90.245.2/29, Area 0 
  Process ID 1, Router ID 10.90.20.1, Network Type POINT_TO_MULTIPOINT,
Cost: 64
  Transmit Delay is 1 sec, State POINT_TO_MULTIPOINT
  Timer intervals configured, Hello 30, Dead 120, Wait 120, Retransmit 5
    oob-resync timeout 120
    Hello due in 00:00:05
  Supports Link-local Signaling (LLS)
  Cisco NSF helper support enabled
  IETF NSF helper support enabled
  Index 1/1, flood queue length 0
  Next 0x0(0)/0x0(0)
  Last flood scan length is 1, maximum is 1
  Last flood scan time is 0 msec, maximum is 4 msec
  Neighbor Count is 1, Adjacent neighbor count is 1 
    Adjacent with neighbor 10.90.10.1
  Suppress hello for 0 neighbor(s)
R2#

R4#show ip ospf interface Serial0/0
Serial0/0 is up, line protocol is up 
  Internet Address 10.90.245.4/29, Area 0 
  Process ID 1, Router ID 10.90.40.1, Network Type POINT_TO_MULTIPOINT,
Cost: 64
  Transmit Delay is 1 sec, State POINT_TO_MULTIPOINT
  Timer intervals configured, Hello 30, Dead 120, Wait 120, Retransmit 5
    oob-resync timeout 120
    Hello due in 00:00:08
  Supports Link-local Signaling (LLS)
  Cisco NSF helper support enabled
  IETF NSF helper support enabled
  Index 1/1, flood queue length 0
  Next 0x0(0)/0x0(0)
  Last flood scan length is 1, maximum is 1
  Last flood scan time is 0 msec, maximum is 4 msec
  Neighbor Count is 1, Adjacent neighbor count is 1 
    Adjacent with neighbor 10.90.10.1
  Suppress hello for 0 neighbor(s)
R4#

R5#show ip ospf interface Serial0/0
Serial0/0 is up, line protocol is up 
  Internet Address 10.90.245.5/29, Area 0 
  Process ID 1, Router ID 10.90.50.1, Network Type POINT_TO_MULTIPOINT,
Cost: 64
  Transmit Delay is 1 sec, State POINT_TO_MULTIPOINT
  Timer intervals configured, Hello 30, Dead 120, Wait 120, Retransmit 5
    oob-resync timeout 120
    Hello due in 00:00:01
  Supports Link-local Signaling (LLS)
  Cisco NSF helper support enabled
  IETF NSF helper support enabled
  Index 1/1, flood queue length 0
  Next 0x0(0)/0x0(0)
  Last flood scan length is 1, maximum is 1
  Last flood scan time is 4 msec, maximum is 4 msec
  Neighbor Count is 1, Adjacent neighbor count is 1 
    Adjacent with neighbor 10.90.10.1
  Suppress hello for 0 neighbor(s)
R5#

Objective 3. – Verify the neighbor relationships on R1 by viewing the neighbor table.

R1#show ip ospf neighbor

Neighbor ID     Pri   State           Dead Time   Address         Interface
10.90.50.1        0   FULL/  -        00:01:53    10.90.245.5      Serial0/0
10.90.40.1        0   FULL/  -        00:01:58    10.90.245.4      Serial0/0
10.90.20.1        0   FULL/  -        00:01:50    10.90.245.2      Serial0/0
R1#

As you can see from the neighbor table on R1 that no DR/BDR is elected when using the OSPF point-to-multipoint network type because each neighbor relationship is treated as a point-to-point link.

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