The default OSPF network type on multipoint interfaces–the nonbroadcast network type–prevents OSPF from working without further configuration.
The actions to take for the issues related to neighbor discovery:
■ If the configured network type allows for neighbor discovery using Hellos (Broadcast, Point-to-multipoint), and you use InARP, the neighbors should be discovered.
■ If the configured network type allows for neighbor discovery (Broadcast, Point-to-multipoint), and you use frame-relay map, ensure that the broadcast keyword is included.
■ If the configured network type does not allow for neighbor discovery (Nonbroadcast, Point-to-multipoint nonbroadcast), statically configure neighbors.
When using subinterfaces, IOS needs a command under a Frame Relay subinterface that associates each PVC with that subinterface: either a "frame-relay interface-dlci" command or a "frame-relay map" command.
-The "frame-relay interface-dlci" command just associates the DLCI with the subinterface, relying on Frame Relay InARP to discover mappings.
-The second command ("frame-relay map") statically configures that mapping, while also associating the DLCI with the subinterface.
For a Frame Relay partial mesh to work when also using an OSPF DR, a PVC must exist between any two routers that need to perform database exchange directly with each other.
In short, the following PVCs must exist:
■ Between the DR and every other router in the subnet
■ Between the BDR and every other router in the subnet
Summarizing the key points:
■ If using a network type that requires a DR/BDR, restrict the role of DR and BDR to routers that have a PVC connecting to all other routers (hub routers).
■ Configure the OSPF network type to avoid using a DR/BDR.
Rule: For any routers without a direct PVC, statically configure an IP-address-to-DLCI mapping with the other router’s next-hop IP address, and a DLCI that does
connect to a router that has PVCs with each of the two routers. (For hub-and-spoke networks configure Frame Relay IP-address-to-DLCI mapping also between the spokes, even if they already have OSPF routes to each other.)
-For Broadcast OSPF network type the Hello interval is 10 seconds.
-For all other OSPF network types the Hello interval is 30 seconds.
A. Considering a Non-Broadcast (NBMA) setup between R9, R10, R11:
By using the (default) network type setting of nonbroadcast, all four routers will elect a DR and BDR.
They also will not attempt to multicast Hellos to discover each other, so they need to configure each other in OSPF "neighbor" commands.
Note: The "neighbor" command does not have to be configured on both the hub and the spoke. Configuring it on the hub router is enough to bring up the OSPF neighborship.
We need to restrict routers so that only routers with PVCs to all other routers (hub routers) are allowed to become DR or BDR (using the "ip ospf priority 0" command on the spokes).
R9#show ip ospf interface serial 0/1.1
Serial0/1.1 is up, line protocol is up
Internet Address 10.0.1.1/29, Area 2
Process ID 1, Router ID 9.9.9.9, Network Type NON_BROADCAST, Cost: 64
Transmit Delay is 1 sec, State DR, Priority 1
Designated Router (ID) 9.9.9.9, Interface address 10.0.1.1
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 00:00:00
Supports Link-local Signaling (LLS)
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 0, Adjacent neighbor count is 0
Suppress hello for 0 neighbor(s)
R9(config)#interface serial 0/1.1 multipoint
R9(config-subif)#frame-relay map ip 10.0.1.2 102 broadcast
R9(config-subif)#frame-relay map ip 10.0.1.3 103 broadcast
R9(config)#router ospf 1
R9(config-router)#neighbor 10.0.1.2
R9(config-router)#neighbor 10.0.1.3
R10(config)#interface serial 0/0.1 multipoint
R10(config-subif)#frame-relay map ip 10.0.1.1 201 broadcast
R10(config-subif)#ip ospf priority 0
R10(config)#router ospf 1
R10(config-router)#neighbor 10.0.1.1
R11(config)#interface serial 0/0.1 multipoint
R11(config-subif)#frame-relay map ip 10.0.1.1 301 broadcast
R11(config-subif)#ip ospf priority 0
R11(config)#router ospf 1
R11(config-router)#neighbor 10.0.1.1
Pings between R10 and R11 still do not work until we configure Frame Relay mappings on each router to the other router:
R10#ping 10.0.1.3
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.0.1.3, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)
R11#ping 10.0.1.2
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.0.1.2, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)
R10(config)#interface serial 0/0.1 multipoint
R10(config-subif)#frame-relay map ip 10.0.1.3 201 broadcast
R11(config)#interface serial 0/0.1 multipoint
R11(config-subif)#frame-relay map ip 10.0.1.2 301 broadcast
Now pings are working between the spoke routers:
R10#ping 10.0.1.3
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.0.1.3, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/29/80 ms
R11#ping 10.0.1.2
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.0.1.2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/29/108 ms
After configuring R10 and R11 with the "ip ospf priority 0" command, R9 is elected as DR and both spoke routers are DROthers:
R9#show ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
10.10.10.10 0 FULL/DROTHER 00:01:31 10.0.1.2 Serial0/1.1
11.11.11.11 0 FULL/DROTHER 00:01:51 10.0.1.3 Serial0/1.1
12.12.12.12 1 FULL/DR 00:00:39 192.168.3.2 FastEthernet0/0
R9#show ip ospf interface serial 0/1.1
Serial0/1.1 is up, line protocol is up
Internet Address 10.0.1.1/29, Area 2
Process ID 1, Router ID 9.9.9.9, Network Type NON_BROADCAST, Cost: 64
Transmit Delay is 1 sec, State DR, Priority 1
Designated Router (ID) 9.9.9.9, Interface address 10.0.1.1
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 00:00:29
Supports Link-local Signaling (LLS)
Index 1/1, flood queue length 0
Next 0x0(0)/0x0(0)
Last flood scan length is 1, maximum is 10
Last flood scan time is 4 msec, maximum is 4 msec
Neighbor Count is 2, Adjacent neighbor count is 2
Adjacent with neighbor 10.10.10.10
Adjacent with neighbor 11.11.11.11
Suppress hello for 0 neighbor(s)
B. Considering a Point-to-multipoint setup between R9, R10, R11:
Network type point-to-multipoint tells routers to act oppositely compared to the nonbroadcast type: to not elect a DR/BDR and to dynamically discover neighbors.
Also, note that the routers without PVCs to each other router still require the frame-relay map commands.
R9(config)#interface serial 0/1.1 multipoint
R9(config-subif)#frame-relay map ip 10.0.1.2 102 broadcast
R9(config-subif)#frame-relay map ip 10.0.1.3 103 broadcast
R9(config-subif)#ip ospf network point-to-multipoint
R10(config)#interface serial 0/0.1 multipoint
R10(config-subif)#frame-relay map ip 10.0.1.1 201 broadcast
R10(config-subif)#frame-relay map ip 10.0.1.3 201 broadcast
R10(config-subif)#ip ospf network point-to-multipoint
R11(config)#interface serial 0/0.1 multipoint
R11(config-subif)#frame-relay map ip 10.0.1.1 301 broadcast
R11(config-subif)#frame-relay map ip 10.0.1.2 301 broadcast
R11(config-subif)#ip ospf network point-to-multipoint
R9#show ip ospf interface serial 0/1.1
Serial0/1.1 is up, line protocol is up
Internet Address 10.0.1.1/29, Area 2
Process ID 1, Router ID 9.9.9.9, 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 00:00:03
Supports Link-local Signaling (LLS)
Index 1/1, 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)
Neighbors are dynamically discovered, without the use of the "neighbor" command and no DR/BDR are elected:
R9#show ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
1.1.1.1 0 FULL/ - 00:00:39 192.168.0.21 Serial0/0
11.11.11.11 0 FULL/ - 00:01:38 10.0.1.3 Serial0/1.1
10.10.10.10 0 FULL/ - 00:01:30 10.0.1.2 Serial0/1.1
12.12.12.12 1 FULL/DR 00:00:39 192.168.3.2 FastEthernet0/0
Pings work between the hub and the spokes and between the spokes:
R10#ping 10.0.1.3
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.0.1.3, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/26/68 ms
R11#ping 10.0.1.2
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.0.1.2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/25/100 ms
C. Considering a Point-to-multipoint nonbroadcast setup between R9, R10, R11:
OSPF network type point-to-multipoint nonbroadcast tells routers to act like the similarly named point-to-multipoint type by not electing a DR/BDR.
However, the difference lies in neighbor discovery–the keyword “nonbroadcast” implies that the routers cannot broadcast (or multicast) to discover neighbors.
Also, regardless of network type, for those routers without direct PVCs, Frame Relay mapping must be added.
Using the same configuration as above, we can change the OSPF network type of the multipoint subinterfaces on all three routers:
R9(config)#interface serial 0/1.1 multipoint
R9(config-subif)#ip ospf network point-to-multipoint non-broadcast
*Mar 1 01:04:07.227: %OSPF-5-ADJCHG: Process 1, Nbr 11.11.11.11 on Serial0/1.1 from FULL to DOWN, Neighbor Down: Interface down or detached
*Mar 1 01:04:07.227: %OSPF-5-ADJCHG: Process 1, Nbr 10.10.10.10 on Serial0/1.1 from FULL to DOWN, Neighbor Down: Interface down or detached
R10(config-subif)#ip ospf network point-to-multipoint non-broadcast
R10(config-subif)#
*Mar 1 02:18:03.835: %OSPF-5-ADJCHG: Process 1, Nbr 9.9.9.9 on Serial0/0.1 from FULL to DOWN, Neighbor Down: Interface down or detached
R11(config-subif)#ip ospf network point-to-multipoint non-broadcast
R11(config-subif)#
*Mar 1 02:18:34.707: %OSPF-5-ADJCHG: Process 1, Nbr 9.9.9.9 on Serial0/0.1 from FULL to DOWN, Neighbor Down: Interface down or detached
Modifying the OSPF network type to point-to-multipoint NONBROADCAST, the neighborships fail because neighbor discovery is turned off now, requiring the "neighbor" command:
R9#show ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
1.1.1.1 0 FULL/ - 00:00:37 192.168.0.21 Serial0/0
12.12.12.12 1 FULL/DR 00:00:37 192.168.3.2 FastEthernet0/0
R9#show ip ospf interface serial 0/1.1
Serial0/1.1 is up, line protocol is up
Internet Address 10.0.1.1/29, Area 2
Process ID 1, Router ID 9.9.9.9, 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 00:00:14
Supports Link-local Signaling (LLS)
Index 1/1, flood queue length 0
Next 0x0(0)/0x0(0)
Last flood scan length is 1, maximum is 9
Last flood scan time is 0 msec, maximum is 4 msec
Neighbor Count is 0, Adjacent neighbor count is 0
Suppress hello for 0 neighbor(s)
After statically configuring neighbors on R9 the OSPF neighborships are formed again. There is no need to configure the "neighbor" command on the spoke routers also.
R9(config)#router ospf 1
R9(config-router)#neighbor 10.0.1.2
R9(config-router)#neighbor 10.0.1.3
R9(config-router)#
*Mar 1 01:13:07.327: %OSPF-5-ADJCHG: Process 1, Nbr 11.11.11.11 on Serial0/1.1 from LOADING to FULL, Loading Done
*Mar 1 01:13:07.343: %OSPF-5-ADJCHG: Process 1, Nbr 10.10.10.10 on Serial0/1.1 from LOADING to FULL, Loading Done
Neighbors are up again, not electing any DR/BDR:
R9#show ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
1.1.1.1 0 FULL/ - 00:00:39 192.168.0.21 Serial0/0
11.11.11.11 0 FULL/ - 00:01:49 10.0.1.3 Serial0/1.1
10.10.10.10 0 FULL/ - 00:01:49 10.0.1.2 Serial0/1.1
12.12.12.12 1 FULL/DR 00:00:39 192.168.3.2 FastEthernet0/0
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