Frame relay and inverse-arp

no frame-relay inverse arp says that I shall not ask the other end what his IP address is.

no arp frame-relay means that if the other end asks me my IP address, I shall not answer him.

OSPF - Network Types

OSPF Network Types are:
BROADCAST, DR/BDR election, auto neighbor, 10s hello.
NON_BROADCAST, DR/BDR election, configured neighbor, 30s hello.


POINT_TO_POINT, no DR/BDR election, auto neighbor, 10s hello.
POINT_TO_MULTIPOINT, no DR/BDR election, configured neighbor, 30s hello.
POINT_TO_MULTIPOINT NON_BROADCAST, no DR/BDR election, configured neighbor, 30s hello.

Avoid mixing of OSPF Network types that works with DR/BDR and those that don't.


On Ethernet segments, use:
BROADCAST (default) , if more than two routers on the segment.
POINT_TO_POINT, if only two routers on the segment.
POINT_TO_MULTIPOINT NON_BROADCAST, usefull to configure neighbor costs, but there should be a full mesh configuration.


On NBMA, use:

NON_BROADCAST (default), use if the mapping is fully configured (static mapping only or dynamic mapping plus static mapping allowed) or at least if all spokes have connectivity with the Hub.

BROADCAST, broadcast must be enabled on each mapping.

POINT_TO_POINT, can be configured on the spokes if the Hub is configured in POINT_TO_MULTIPOINT, but change timers.

POINT_TO_MULTIPOINT, if the mapping is not fully configured (dynamic mapping only) and no BDR are allowed.

POINT_TO_MULTIPOINT NON_BROADCAST, if the mapping is not fully configured (dynamic mapping only or static mapping (to the HUB only or not) but without broadcast keyword) and no BDR are allowed.

On serial links, use:

POINT_TO_POINT (default)

OSPF - Network Type POINT_TO_MULTIPOINT NON_BROADCAST

POINT_TO_MULTIPOINT NON_BROADCAST is a mix of POINT_TO_MULTIPOINT and NON_BROADCAST network types. The best of each network type is used.

POINT_TO_MULTIPOINT means no DR/BDR election. This also signify that the hub sees each adjacency as a point-to point link and that the NEXT-HOP is always the HUB (so, partial mesh frame relay configuration is possible, for example dynamic mapping with no knowledge of the dlci to use to reach another spoke).

NON_BROADCAST means manual configuration of the neighbors. The costs can be specified on a per neighbor basis, through the neighbor command. This is useful on NBMA networks.

On r1:

!

interface Serial0/0

 ip address 150.0.0.1 255.255.255.0

 encapsulation frame-relay

 ip ospf network point-to-multipoint non-broadcast

 frame-relay map ip 150.0.0.2 102 broadcast

 frame-relay map ip 150.0.0.3 103 broadcast

 no frame-relay inverse-arp

!

router ospf 1

 router-id 150.1.1.1

 log-adjacency-changes

 passive-interface Loopback0

 network 150.0.0.1 0.0.0.0 area 0

 network 150.1.1.1 0.0.0.0 area 0

 network 150.10.0.11 0.0.0.0 area 0

 neighbor 150.0.0.3

 neighbor 150.0.0.2

!

r1#show ip ospf neighbor

Neighbor ID     Pri   State           Dead Time   Address         Interface

150.3.3.3         0   FULL/  -        00:01:42    150.0.0.3       Serial0/0

150.2.2.2         0   FULL/  -        00:01:42    150.0.0.2       Serial0/0

r1#

On r2:

!

interface Serial0/0

 ip address 150.0.0.2 255.255.255.0

 encapsulation frame-relay

 ip ospf network point-to-multipoint non-broadcast

 frame-relay map ip 150.0.0.1 201 broadcast

 frame-relay map ip 150.0.0.3 201

 frame-relay map ip 150.0.0.4 201

 no frame-relay inverse-arp

!

router ospf 1

 router-id 150.2.2.2

 log-adjacency-changes

 passive-interface Loopback0

 network 150.0.0.2 0.0.0.0 area 0

 network 150.2.2.2 0.0.0.0 area 0

! 

r2#show ip ospf neighbor

Neighbor ID     Pri   State           Dead Time   Address         Interface

150.1.1.1         0   FULL/  -        00:01:54    150.0.0.1       Serial0/0

r2#

r2#show ip route ospf

     150.0.0.0/16 is variably subnetted, 3 subnets, 2 masks

O       150.0.0.3/32 [110/128] via 150.0.0.1, 00:22:52, Serial0/0

O       150.0.0.1/32 [110/64] via 150.0.0.1, 00:22:52, Serial0/0

     150.1.0.0/32 is subnetted, 1 subnets

O       150.1.1.1 [110/65] via 150.0.0.1, 00:22:52, Serial0/0

     150.3.0.0/32 is subnetted, 1 subnets

O       150.3.3.3 [110/129] via 150.0.0.1, 00:22:52, Serial0/0

     150.10.0.0/24 is subnetted, 1 subnets

O       150.10.0.0 [110/65] via 150.0.0.1, 00:22:52, Serial0/0

r2#

r2#show ip ospf interface Serial 0/0

Serial0/0 is up, line protocol is up

  Internet Address 150.0.0.2/24, Area 0

  Process ID 1, Router ID 150.2.2.2, 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 00:00:27

  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 150.1.1.1

  Suppress hello for 0 neighbor(s)

r2#show ip ospf database router 150.3.3.3

            OSPF Router with ID (150.2.2.2) (Process ID 1)

          Router Link States (Area 0)

  LS age: 1704

  Options: (No TOS-capability, DC)

  LS Type: Router Links

  Link State ID: 150.3.3.3

  Advertising Router: 150.3.3.3

  LS Seq Number: 80000022

  Checksum: 0xCD39

  Length: 60

  Number of Links: 3

    Link connected to: a Stub Network

     (Link ID) Network/subnet number: 150.3.3.3

     (Link Data) Network Mask: 255.255.255.255

      Number of TOS metrics: 0

       TOS 0 Metrics: 1

    Link connected to: another Router (point-to-point)

     (Link ID) Neighboring Router ID: 150.1.1.1

     (Link Data) Router Interface address: 150.0.0.3

      Number of TOS metrics: 0

       TOS 0 Metrics: 64

    Link connected to: a Stub Network

     (Link ID) Network/subnet number: 150.0.0.3

     (Link Data) Network Mask: 255.255.255.255

      Number of TOS metrics: 0

       TOS 0 Metrics: 0

There is a new stub network, 150.3.3.3 with mask 255.255.255.255 which is entered in the routing table as 150.3.3.3/32.

Note:

The mapping on the spoke is only necessary toward the HUB. Moreover, the broadcast keyword is optional.

The cost can be specified on a per neighbor basis.

On r1:

!

interface Serial0/0

 ip address 150.0.0.1 255.255.255.0

 encapsulation frame-relay

 ip ospf network point-to-multipoint non-broadcast

 frame-relay map ip 150.0.0.2 102

 frame-relay map ip 150.0.0.3 103

 no frame-relay inverse-arp

!

router ospf 1

 router-id 150.1.1.1

 log-adjacency-changes

 passive-interface Loopback0

 network 150.0.0.1 0.0.0.0 area 0

 network 150.1.1.1 0.0.0.0 area 0

 network 150.10.0.11 0.0.0.0 area 0

 neighbor 150.0.0.3 cost 100

 neighbor 150.0.0.2 cost 20

!         

On r2:

!

interface Serial0/0

 ip address 150.0.0.2 255.255.255.0

 encapsulation frame-relay

 ip ospf network point-to-multipoint non-broadcast

 frame-relay map ip 150.0.0.1 201

 no frame-relay inverse-arp

!

On r3:

!

interface Serial0/0

 ip address 150.0.0.3 255.255.255.0

 encapsulation frame-relay

 ip ospf network point-to-multipoint non-broadcast

 frame-relay map ip 150.0.0.1 301

 no frame-relay inverse-arp

!

r1# show  ip route ospf

     150.0.0.0/16 is variably subnetted, 3 subnets, 2 masks

O       150.0.0.2/32 [110/20] via 150.0.0.2, 00:01:16, Serial0/0

O       150.0.0.3/32 [110/100] via 150.0.0.3, 00:01:16, Serial0/0

     150.2.0.0/32 is subnetted, 1 subnets

O       150.2.2.2 [110/21] via 150.0.0.2, 00:01:16, Serial0/0

     150.3.0.0/32 is subnetted, 1 subnets

O       150.3.3.3 [110/101] via 150.0.0.3, 00:01:16, Serial0/0

r1# show frame-relay map

Serial0/0 (up): ip 150.0.0.2 dlci 102(0x66,0x1860), static,

              CISCO, status defined, active

Serial0/0 (up): ip 150.0.0.3 dlci 103(0x67,0x1870), static,

              CISCO, status defined, active

r1#show ip ospf neighbor detail

 Neighbor 150.3.3.3, interface address 150.0.0.3

    In the area 0 via interface Serial0/0

    Neighbor priority is 0 (configured 0), State is FULL, 13 state changes, Cost is 100

    DR is 0.0.0.0 BDR is 0.0.0.0

    Options is 0x52

    LLS Options is 0x1 (LR)

    Dead timer due in 00:01:47

    Neighbor is up for 00:04:58

    Index 2/2, retransmission queue length 0, number of retransmission 4

    First 0x0(0)/0x0(0) Next 0x0(0)/0x0(0)

    Last retransmission scan length is 1, maximum is 1

    Last retransmission scan time is 0 msec, maximum is 0 msec

 Neighbor 150.2.2.2, interface address 150.0.0.2

    In the area 0 via interface Serial0/0

    Neighbor priority is 0 (configured 0), State is FULL, 13 state changes, Cost is 20

    DR is 0.0.0.0 BDR is 0.0.0.0

    Options is 0x52

    LLS Options is 0x1 (LR)

    Dead timer due in 00:01:47

    Neighbor is up for 00:04:58

    Index 1/1, retransmission queue length 0, number of retransmission 1

    First 0x0(0)/0x0(0) Next 0x0(0)/0x0(0)

    Last retransmission scan length is 1, maximum is 1

    Last retransmission scan time is 0 msec, maximum is 0 msec

r2#show ip route ospf

     150.0.0.0/16 is variably subnetted, 3 subnets, 2 masks

O       150.0.0.3/32 [110/164] via 150.0.0.1, 00:01:17, Serial0/0

O       150.0.0.1/32 [110/64] via 150.0.0.1, 00:01:17, Serial0/0

     150.1.0.0/32 is subnetted, 1 subnets

O       150.1.1.1 [110/65] via 150.0.0.1, 00:01:17, Serial0/0

     150.3.0.0/32 is subnetted, 1 subnets

O       150.3.3.3 [110/165] via 150.0.0.1, 00:01:17, Serial0/0

     150.10.0.0/24 is subnetted, 1 subnets

O       150.10.0.0 [110/65] via 150.0.0.1, 00:01:17, Serial0/0

r2#show frame-relay map

Serial0/0 (up): ip 150.0.0.1 dlci 201(0xC9,0x3090), static,

              CISCO, status defined, active

r3#show  ip route ospf

     150.0.0.0/16 is variably subnetted, 3 subnets, 2 masks

O       150.0.0.2/32 [110/84] via 150.0.0.1, 00:01:50, Serial0/0

O       150.0.0.1/32 [110/64] via 150.0.0.1, 00:01:50, Serial0/0

     150.1.0.0/32 is subnetted, 1 subnets

O       150.1.1.1 [110/65] via 150.0.0.1, 00:01:50, Serial0/0

     150.2.0.0/32 is subnetted, 1 subnets

O       150.2.2.2 [110/85] via 150.0.0.1, 00:01:50, Serial0/0

     150.10.0.0/24 is subnetted, 1 subnets

O       150.10.0.0 [110/65] via 150.0.0.1, 00:01:50, Serial0/0

r3#show frame-relay map

Serial0/0 (up): ip 150.0.0.1 dlci 301(0x12D,0x48D0), static,

              CISCO, status defined, active

Note:

Since the beginning of the example, the loopback configured on each router is a /24 but a /32 is advertised. This is because loopback have always the LOOPBACK network type. To change this, use ip ospf network point-to-point.

On r3:

r3#show ip ospf interface Loopback 0

Loopback0 is up, line protocol is up

  Internet Address 150.3.3.3/24, Area 0

  Process ID 1, Router ID 150.3.3.3, Network Type LOOPBACK, Cost: 1

  Loopback interface is treated as a stub Host

r2#show ip route  150.3.3.3   

Routing entry for 150.3.3.3/32

  Known via "ospf 1", distance 110, metric 165, type intra area

  Last update from 150.0.0.1 on Serial0/0, 00:00:55 ago

  Routing Descriptor Blocks:

  * 150.0.0.1, from 150.3.3.3, 00:00:55 ago, via Serial0/0

      Route metric is 165, traffic share count is 1

After configuring the network type:

!

interface Loopback0

 ip address 150.3.3.3 255.255.255.0

 ip ospf network point-to-point

!

r3#show ip ospf interface Loopback 0

Loopback0 is up, line protocol is up

  Internet Address 150.3.3.3/24, Area 0

  Process ID 1, Router ID 150.3.3.3, Network Type POINT_TO_POINT, Cost: 1

  Transmit Delay is 1 sec, State POINT_TO_POINT

  Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5

    oob-resync timeout 40

    No Hellos (Passive interface)

  Supports Link-local Signaling (LLS)

  Cisco NSF helper support enabled

  IETF NSF helper support enabled

  Index 2/2, flood queue length 0

  Next 0x0(0)/0x0(0)

  Last flood scan length is 0, maximum is 0

  Last flood scan time is 0 msec, maximum is 0 msec

  Neighbor Count is 0, Adjacent neighbor count is 0

  Suppress hello for 0 neighbor(s)

Now, this route is seen as a /24 on r2:

r2#show ip route  150.3.3.3

Routing entry for 150.3.3.0/24

  Known via "ospf 1", distance 110, metric 165, type intra area

  Last update from 150.0.0.1 on Serial0/0, 00:00:05 ago

  Routing Descriptor Blocks:

  * 150.0.0.1, from 150.3.3.3, 00:00:05 ago, via Serial0/0

      Route metric is 165, traffic share count is 1

These changes are reflected in the database:

r2#show ip ospf database router 150.3.3.3

            OSPF Router with ID (150.2.2.2) (Process ID 1)

          Router Link States (Area 0)

  LS age: 54

  Options: (No TOS-capability, DC)

  LS Type: Router Links

  Link State ID: 150.3.3.3

  Advertising Router: 150.3.3.3

  LS Seq Number: 80000026

  Checksum: 0xA75E

  Length: 60

  Number of Links: 3

    Link connected to: a Stub Network

     (Link ID) Network/subnet number: 150.3.3.0

     (Link Data) Network Mask: 255.255.255.0

      Number of TOS metrics: 0

       TOS 0 Metrics: 1

    Link connected to: another Router (point-to-point)

     (Link ID) Neighboring Router ID: 150.1.1.1

     (Link Data) Router Interface address: 150.0.0.3

      Number of TOS metrics: 0

       TOS 0 Metrics: 64

    Link connected to: a Stub Network

     (Link ID) Network/subnet number: 150.0.0.3

     (Link Data) Network Mask: 255.255.255.255

      Number of TOS metrics: 0

       TOS 0 Metrics: 0

OSPF - Network Type POINT_TO_MULTIPOINT

With this OSPF Network type, the network is seen as a collection of logical point-to-point links established between each spoke and the hub.

So, with this network type, no DR is elected. Hello packets are still multicast (224.0.0.5).

The configuration is quite simple on Hub and Spoke, configure the interface type as point-to-multipoint.

On r1:

!

interface Serial0/0

 ip address 150.0.0.1 255.255.255.0

 encapsulation frame-relay

 ip ospf network point-to-multipoint

 frame-relay map ip 150.0.0.2 102 broadcast

 frame-relay map ip 150.0.0.3 103 broadcast

 frame-relay map ip 150.0.0.4 104 broadcast

 no frame-relay inverse-arp

!

router ospf 1

 router-id 150.1.1.1

 log-adjacency-changes

 passive-interface Loopback0

 network 150.0.0.1 0.0.0.0 area 0

 network 150.1.1.1 0.0.0.0 area 0

 network 150.10.0.11 0.0.0.0 area 0

!

r1#show ip ospf neighbor 

Neighbor ID     Pri   State           Dead Time   Address         Interface

55.0.0.5          0   FULL/  -        00:00:37    150.10.0.15     FastEthernet0/0

150.4.4.4         0   FULL/  -        00:01:33    150.0.0.4       Serial0/0

150.2.2.2         0   FULL/  -        00:01:53    150.0.0.2       Serial0/0

150.3.3.3         0   FULL/  -        00:01:33    150.0.0.3       Serial0/0

r5#

On the spokes:

r2:

!

interface Serial0/0

 ip address 150.0.0.2 255.255.255.0

 encapsulation frame-relay

 ip ospf network point-to-multipoint

 frame-relay map ip 150.0.0.1 201 broadcast

 frame-relay map ip 150.0.0.3 201

 frame-relay map ip 150.0.0.4 201

 no frame-relay inverse-arp

!

router ospf 1

 router-id 150.2.2.2

 log-adjacency-changes

 passive-interface Loopback0

 network 150.0.0.2 0.0.0.0 area 0

 network 150.2.2.2 0.0.0.0 area 0

!

r2#show ip ospf  neighbor

Neighbor ID     Pri   State           Dead Time   Address         Interface

150.1.1.1         0   FULL/  -        00:01:43    150.0.0.1       Serial0/0

r2#

As these adjacencies are seen as point-to-point between the Hub and a given Spoke, the NEXT-HOP is modified by the Hub:

r2#show ip route ospf

     55.0.0.0/32 is subnetted, 1 subnets

O       55.0.0.5 [110/66] via 150.0.0.1, 01:03:56, Serial0/0

     150.0.0.0/16 is variably subnetted, 4 subnets, 2 masks

O       150.0.0.4/32 [110/128] via 150.0.0.1, 01:03:46, Serial0/0

O       150.0.0.3/32 [110/128] via 150.0.0.1, 01:03:56, Serial0/0

O       150.0.0.1/32 [110/64] via 150.0.0.1, 01:03:56, Serial0/0

     150.1.0.0/32 is subnetted, 1 subnets

O       150.1.1.1 [110/65] via 150.0.0.1, 01:03:56, Serial0/0

     150.3.0.0/32 is subnetted, 1 subnets

O       150.3.3.3 [110/129] via 150.0.0.1, 01:03:56, Serial0/0

     150.4.0.0/32 is subnetted, 1 subnets

O       150.4.4.4 [110/129] via 150.0.0.1, 01:03:46, Serial0/0

     150.10.0.0/24 is subnetted, 1 subnets

O       150.10.0.0 [110/65] via 150.0.0.1, 01:03:56, Serial0/0

r2# 

As a result, there can be a single mapping on the spokes, indicating the dlci towards the Hub. This is usefull if dynamic mapping is used because dynamic mapping can't give the mapping for a spoke to reach another spoke. With this network type, this is not a problem.

We can see in the OSPF database that the link between the spokes and the hub is seen as a point-to-point link:

r2#show ip ospf database router 150.3.3.3

            OSPF Router with ID (150.2.2.2) (Process ID 1)

          Router Link States (Area 0)

  LS age: 84

  Options: (No TOS-capability, DC)

  LS Type: Router Links

  Link State ID: 150.3.3.3

  Advertising Router: 150.3.3.3

  LS Seq Number: 8000000E

  Checksum: 0xF525

  Length: 60

  Number of Links: 3

    Link connected to: a Stub Network

     (Link ID) Network/subnet number: 150.3.3.3

     (Link Data) Network Mask: 255.255.255.255

      Number of TOS metrics: 0

       TOS 0 Metrics: 1

    Link connected to: another Router (point-to-point)

     (Link ID) Neighboring Router ID: 150.1.1.1

     (Link Data) Router Interface address: 150.0.0.3

      Number of TOS metrics: 0

       TOS 0 Metrics: 64

    Link connected to: a Stub Network

     (Link ID) Network/subnet number: 150.0.0.3

     (Link Data) Network Mask: 255.255.255.255

      Number of TOS metrics: 0

       TOS 0 Metrics: 0

Using ospf network POINT_TO_MULTIPOINT type in Hub & Spoke topology does not requires that a mapping exists on each spokes to reach other spoke. The mapping to the Hub is mandatory because it will be NEXT-HOP for each route.

OSPF - Network Type NON_BROADCAST

Default mode for Frame-Relay main interfaces and multipoint subinterfaces.

In Hub & Spoke topology, the Hub MUST be the DR. Spoke not always have connectivity with other routers.

On the Spokes, configure ip ospf priority 0.

In this mode, you have to configure neighbors on the HUB router. There is no need to configure the neighbor on the Spokes: spokes will reply to unicast hellos from the Hub.

On r1:

!

interface Loopback0

 ip address 150.1.1.1 255.255.255.0

!

interface FastEthernet0/0

 ip address 150.10.0.11 255.255.255.0

 ip ospf network point-to-point

 duplex auto

 speed auto

!

interface Serial0/0

 ip address 150.0.0.1 255.255.255.0

 encapsulation frame-relay

 frame-relay map ip 150.0.0.4 104 broadcast

 frame-relay map ip 150.0.0.3 103 broadcast

 frame-relay map ip 150.0.0.2 102 broadcast

 no frame-relay inverse-arp

!

router ospf 1

 router-id 150.1.1.1

 log-adjacency-changes

 passive-interface Loopback0

 network 150.0.0.1 0.0.0.0 area 0

 network 150.1.1.1 0.0.0.0 area 0

 network 150.10.0.11 0.0.0.0 area 0

 neighbor 150.0.0.2

 neighbor 150.0.0.3

 neighbor 150.0.0.4

!

R1 S0/0 is NON_BROADCAST and R1 is the DR (default priority is 1).
Three neighbors are configured.

r1#show ip ospf interface S0/0

Serial0/0 is up, line protocol is up

  Internet Address 150.0.0.1/24, Area 0

  Process ID 1, Router ID 150.1.1.1, Network Type NON_BROADCAST, Cost: 64

  Transmit Delay is 1 sec, State DR, Priority 1

  Designated Router (ID) 150.1.1.1, Interface address 150.0.0.1

  No backup designated router on this network

  Timer intervals configured, Hello 30, Dead 120, Wait 120, Retransmit 5

    oob-resync timeout 120

    Hello due in 00:00:24

  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 3, Adjacent neighbor count is 3

    Adjacent with neighbor 150.2.2.2

    Adjacent with neighbor 150.3.3.3

    Adjacent with neighbor 150.4.4.4

  Suppress hello for 0 neighbor(s)

The neighbors are in FULL/DROTHER state, they are no DR, nor BDR.

r1#show ip ospf neighbor

Neighbor ID     Pri   State           Dead Time   Address         Interface

55.0.0.5          0   FULL/  -        00:00:35    150.10.0.15     FastEthernet0/0

150.2.2.2         0   FULL/DROTHER    00:01:59    150.0.0.2       Serial0/0

150.3.3.3         0   FULL/DROTHER    00:01:41    150.0.0.3       Serial0/0

150.4.4.4         0   FULL/DROTHER    00:01:36    150.0.0.4       Serial0/0

r1#

On r2:

!

interface Loopback0

 ip address 150.2.2.2 255.255.255.0

!

interface Serial0/0

 ip address 150.0.0.2 255.255.255.0

 encapsulation frame-relay

 ip ospf priority 0

 frame-relay map ip 150.0.0.4 201

 frame-relay map ip 150.0.0.3 201

 frame-relay map ip 150.0.0.1 201 broadcast

 no frame-relay inverse-arp

!

router ospf 1

 router-id 150.2.2.2

 log-adjacency-changes

 passive-interface Loopback0

 network 150.0.0.2 0.0.0.0 area 0

 network 150.2.2.2 0.0.0.0 area 0

!

r2#show ip ospf interface Serial 0/0

Serial0/0 is up, line protocol is up

  Internet Address 150.0.0.2/24, Area 0

  Process ID 1, Router ID 150.2.2.2, Network Type NON_BROADCAST, Cost: 64

  Transmit Delay is 1 sec, State DROTHER, Priority 0

  Designated Router (ID) 150.1.1.1, Interface address 150.0.0.1

  No backup designated router on this network

  Timer intervals configured, Hello 30, Dead 120, Wait 120, Retransmit 5

    oob-resync timeout 120

    Hello due in 00:00:22

  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 150.1.1.1  (Designated Router)

  Suppress hello for 0 neighbor(s)

r2# 

r2#show ip ospf neighbor 

Neighbor ID     Pri   State           Dead Time   Address         Interface

150.1.1.1         1   FULL/DR         00:01:57    150.0.0.1       Serial0/0

r2#

And so on for r3 and r4.

The routing table on r2 is the following:

r2#show ip route ospf

     55.0.0.0/32 is subnetted, 1 subnets

O       55.0.0.5 [110/66] via 150.0.0.1, 00:03:58, Serial0/0

     150.1.0.0/32 is subnetted, 1 subnets

O       150.1.1.1 [110/65] via 150.0.0.1, 01:11:34, Serial0/0

     150.3.0.0/32 is subnetted, 1 subnets

O       150.3.3.3 [110/65] via 150.0.0.3, 00:15:45, Serial0/0

     150.4.0.0/32 is subnetted, 1 subnets

O       150.4.4.4 [110/65] via 150.0.0.4, 01:10:26, Serial0/0

     150.10.0.0/24 is subnetted, 1 subnets

O       150.10.0.0 [110/65] via 150.0.0.1, 00:08:48, Serial0/0

We can see that the next-hop is handled as on BROADCAST networks. Even if the packets have to go via the Hub, NEXT-HOP is the spoke router that announces the route.
This behaviour implies that frame-relay mapping is present between each spokes.

r2#show ip route 150.4.4.4

Routing entry for 150.4.4.4/32

  Known via "ospf 1", distance 110, metric 65, type intra area

  Last update from 150.0.0.4 on Serial0/0, 00:06:46 ago

  Routing Descriptor Blocks:

  * 150.0.0.4, from 150.4.4.4, 00:06:46 ago, via Serial0/0

      Route metric is 65, traffic share count is 1

r2#show ip route 55.0.0.5

Routing entry for 55.0.0.5/32

  Known via "ospf 1", distance 110, metric 66, type intra area

  Last update from 150.0.0.1 on Serial0/0, 00:10:36 ago

  Routing Descriptor Blocks:

  * 150.0.0.1, from 55.0.0.5, 00:10:36 ago, via Serial0/0

      Route metric is 66, traffic share count is 1

r1 is seen as a transit network, so it has the hability to change the next-hop:

r2#show ip ospf database router 150.4.4.4

            OSPF Router with ID (150.2.2.2) (Process ID 1)

          Router Link States (Area 0)

  LS age: 222

  Options: (No TOS-capability, DC)

  LS Type: Router Links

  Link State ID: 150.4.4.4

  Advertising Router: 150.4.4.4

  LS Seq Number: 8000000B

  Checksum: 0xB608

  Length: 48

  Number of Links: 2

    Link connected to: a Stub Network

     (Link ID) Network/subnet number: 150.4.4.4

     (Link Data) Network Mask: 255.255.255.255

      Number of TOS metrics: 0

       TOS 0 Metrics: 1

    Link connected to: a Transit Network

     (Link ID) Designated Router address: 150.0.0.1

     (Link Data) Router Interface address: 150.0.0.4

      Number of TOS metrics: 0

       TOS 0 Metrics: 64

Notes/Tips/Traps:

Using ospf network NON_BROADCAST type in Hub & Spoke topology requires that a mapping exists on each spokes to reach each other spoke because the spoke's IP address is the next-hop for the prefix it advertises in the NBMA network.

So, if static mapping is not allowed, we are facing an issue with ospf network NON_BROADCAST type.

The broadcast statement in the mapping is not mandatory as the hellos are sent unicast.