In one lab I did in Packet Tracer, I used EIGRP with Frame Relay in a hub and spoke topology. I did not have a problem with this topology except with the issue of split horizon which can be solved by disabling the feature or implementing static routing (more complex solutions are to change the topology to full mesh or use subinterfaces). This is the topology of the network:
The network is working as it should so I thought of migrating it to OSPF. I haven’t encountered this kind of setup in the CCNA Certification Library and was not really discussed in those books. This is the first time I will be using OSPF in this kind of topology so I don’t really know the nature of this network. I usually use OSPF using point-to-point serial connection with HDLC or PPP. So to do that, I disabled EIGRP and applied the basic OSPF configuration which usually accomplishes the objective of having the routers learn the routes in the network:
R1
R2
R3
Before I test the network connectivity using Ping, I waited for the neighbor relationship to come up… and it did not. There was also no output when I issued the show ip ospf neighbor command. I was kind of expecting this result even though I don’t really know the reason behind it. Then I remember that even though there was no example of this kind of setup in the books, it was discussed there that OSPF has different network types which also require different configurations. Frame Relay belongs to the Non-broadcast Multi-access network type. The command for configuring the OSPF network type for a particular interface is ip ospf network type. So I tried this in Packet Tracer and got the following output:
This is now my configuration for R1
The adjacency-changes logs show that neighbor relationship has been established
Now check out the network type configured on the interface
You can see that the network type is configured for non-broadcast.
It’s time to check the routing table
Finally, the ping results
That’s it. We solved the mystery of the non-broadcast ospf network type.
GNS3 topology and PT file
The network is working as it should so I thought of migrating it to OSPF. I haven’t encountered this kind of setup in the CCNA Certification Library and was not really discussed in those books. This is the first time I will be using OSPF in this kind of topology so I don’t really know the nature of this network. I usually use OSPF using point-to-point serial connection with HDLC or PPP. So to do that, I disabled EIGRP and applied the basic OSPF configuration which usually accomplishes the objective of having the routers learn the routes in the network:
hostname R1
!
interface Loopback0
ip address 172.16.1.1 255.255.255.0
!
interface Serial0/0/0
ip address 192.168.1.1 255.255.255.0
encapsulation frame-relay
frame-relay map ip 192.168.1.2 102
frame-relay map ip 192.168.1.3 103
!
router ospf 1
router-id 1.1.1.1
log-adjacency-changes
network 172.16.1.0 0.0.0.255 area 0
network 192.168.1.0 0.0.0.255 area 0
R2
hostname R2
!
interface Loopback0
ip address 172.16.2.1 255.255.255.0
!
interface Serial0/0/0
ip address 192.168.1.2 255.255.255.0
encapsulation frame-relay
frame-relay map ip 192.168.1.1 201
frame-relay map ip 192.168.1.3 201
ip ospf priority 0
!
router ospf 1
router-id 2.2.2.2
log-adjacency-changes
network 172.16.2.0 0.0.0.255 area 0
network 192.168.1.0 0.0.0.255 area 0
!
interface Loopback0
ip address 172.16.2.1 255.255.255.0
!
interface Serial0/0/0
ip address 192.168.1.2 255.255.255.0
encapsulation frame-relay
frame-relay map ip 192.168.1.1 201
frame-relay map ip 192.168.1.3 201
ip ospf priority 0
!
router ospf 1
router-id 2.2.2.2
log-adjacency-changes
network 172.16.2.0 0.0.0.255 area 0
network 192.168.1.0 0.0.0.255 area 0
R3
hostname R3
!
interface Loopback0
ip address 172.16.3.1 255.255.255.0
!
interface Serial0/0/0
ip address 192.168.1.3 255.255.255.0
encapsulation frame-relay
frame-relay map ip 192.168.1.1 301
frame-relay map ip 192.168.1.2 301
ip ospf priority 0
!
router ospf 1
router-id 3.3.3.3
log-adjacency-changes
network 172.16.3.0 0.0.0.255 area 0
network 192.168.1.0 0.0.0.255 area 0
R2(config)#int s0/0/0
R2(config-if)#ip ospf network ?
broadcast Specify OSPF broadcast multi-access network
point-to-point Specify OSPF point-to-point network
Bummer.
I checked the current network type configured in the interface
R2#show ip ospf interface s0/0/0
Serial0/0/0 is up, line protocol is up
Internet address is 192.168.1.2/24, Area 0
Process ID 1, Router ID 2.2.2.2, Network Type MULTI-POINT, Cost: 64
Transmit Delay is 1 sec, State WAITING, Priority 0
No designated router on this network
No backup designated router on this network
Timer intervals configured, Hello 30, Dead 120, Wait 120, Retransmit 5
Hello due in 00:00:13
Index 2/2, 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 0 msec
Neighbor Count is 0, Adjacent neighbor count is 0
Suppress hello for 0 neighbor(s)
Notice the ospf network type configured on the interface, it says MULTI-POINT. Packet Tracer does not support the other OSPF network types. And I got really confused with the output so I decided to just look for the answers in the Internet and I found a very good tutorial on different OSPF network types. It was well-written and there were a lot of router show outputs so everyone can really follow with the discussion. Check out the post I am talking about written by Arden Packeer, CCIE # 20716 by clicking this link.
I learned in his tutorial the missing command in my configuration; the neighbor router subcommand on routers eligible for DR, in this case the hub, R1. This command is also not available in PT. I also learned there that in configuring ospf in Frame Relay network, the network type defaults to non-broadcast.
I also found this excerpt which explains the nature of NBMA networks in accordance with OSPF:
Special care should be taken when configuring OSPF over multi−access non−broadcast medias such as Frame Relay, X.25, ATM. The protocol considers these media like any other broadcast media such as Ethernet. NBMA clouds are usually built in a hub and spoke topology. PVCs or SVCs are laid out in a partial mesh and the physical topology does not provide the multi access that OSPF believes is out there. The selection of the DR becomes an issue because the DR and BDR need to have full physical connectivity with all routers that exist on the cloud. Also, because of the lack of broadcast capabilities, the DR and BDR need to have a static list of all other routers attached to the cloud. This is achieved using the neighbor ip−address [priority number] [poll−interval seconds] command, where the "ip−address" and "priority" are the IP address and the OSPF priority given to the neighbor. A neighbor with priority 0 is considered ineligible for DR election. The "poll−interval" is the amount of time an NBMA interface waits before polling (sending a Hello) to a presumably dead neighbor. The neighbor command applies to routers with a potential of being DRs or BDRs (interface priority not equal to 0).
Armed with the new knowledge and inspiration by Mr. Packeer, I was determined to finish the lab and fired up my GNS3.
This is now my configuration for R1
!
router ospf 1
router-id 1.1.1.1
log-adjacency-changes
network 172.16.1.0 0.0.0.255 area 0
network 192.168.1.0 0.0.0.255 area 0
neighbor 192.168.1.2
neighbor 192.168.1.3
!
router ospf 1
router-id 1.1.1.1
log-adjacency-changes
network 172.16.1.0 0.0.0.255 area 0
network 192.168.1.0 0.0.0.255 area 0
neighbor 192.168.1.2
neighbor 192.168.1.3
!
The adjacency-changes logs show that neighbor relationship has been established
R1#
*Mar 1 00:02:20.219: %OSPF-5-ADJCHG: Process 1, Nbr 3.3.3.3 on Serial0/0 from LOADING to FULL, Loading Done
*Mar 1 00:02:20.227: %OSPF-5-ADJCHG: Process 1, Nbr 2.2.2.2 on Serial0/0 from LOADING to FULL, Loading Done
*Mar 1 00:02:20.219: %OSPF-5-ADJCHG: Process 1, Nbr 3.3.3.3 on Serial0/0 from LOADING to FULL, Loading Done
*Mar 1 00:02:20.227: %OSPF-5-ADJCHG: Process 1, Nbr 2.2.2.2 on Serial0/0 from LOADING to FULL, Loading Done
R1#sh ip ospf neigh
Neighbor ID Pri State Dead Time Address Interface
2.2.2.2 0 FULL/DROTHER 00:01:32 192.168.1.2 Serial0/0
3.3.3.3 0 FULL/DROTHER 00:01:38 192.168.1.3 Serial0/0
Neighbor ID Pri State Dead Time Address Interface
2.2.2.2 0 FULL/DROTHER 00:01:32 192.168.1.2 Serial0/0
3.3.3.3 0 FULL/DROTHER 00:01:38 192.168.1.3 Serial0/0
R2#sh ip ospf neigh
Neighbor ID Pri State Dead Time Address Interface
1.1.1.1 1 FULL/DR 00:01:35 192.168.1.1 Serial0/0
Neighbor ID Pri State Dead Time Address Interface
1.1.1.1 1 FULL/DR 00:01:35 192.168.1.1 Serial0/0
R3#sh ip ospf neigh
Neighbor ID Pri State Dead Time Address Interface
1.1.1.1 1 FULL/DR 00:01:55 192.168.1.1 Serial0/0
Neighbor ID Pri State Dead Time Address Interface
1.1.1.1 1 FULL/DR 00:01:55 192.168.1.1 Serial0/0
Now check out the network type configured on the interface
R1#sh ip ospf interface s0/0
Serial0/0 is up, line protocol is up
Internet Address 192.168.1.1/24, Area 0
Process ID 1, Router ID 1.1.1.1, Network Type NON_BROADCAST, Cost: 64
Transmit Delay is 1 sec, State DR, Priority 1
Designated Router (ID) 1.1.1.1, Interface address 192.168.1.1
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 00:00:19
Supports Link-local Signaling (LLS)
Index 2/2, 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 2, Adjacent neighbor count is 2
Adjacent with neighbor 2.2.2.2
Adjacent with neighbor 3.3.3.3
Suppress hello for 0 neighbor(s)
Serial0/0 is up, line protocol is up
Internet Address 192.168.1.1/24, Area 0
Process ID 1, Router ID 1.1.1.1, Network Type NON_BROADCAST, Cost: 64
Transmit Delay is 1 sec, State DR, Priority 1
Designated Router (ID) 1.1.1.1, Interface address 192.168.1.1
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 00:00:19
Supports Link-local Signaling (LLS)
Index 2/2, 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 2, Adjacent neighbor count is 2
Adjacent with neighbor 2.2.2.2
Adjacent with neighbor 3.3.3.3
Suppress hello for 0 neighbor(s)
You can see that the network type is configured for non-broadcast.
It’s time to check the routing table
R3#sh ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
172.16.0.0/16 is variably subnetted, 3 subnets, 2 masks
O 172.16.1.1/32 [110/65] via 192.168.1.1, 00:06:52, Serial0/0
C 172.16.3.0/24 is directly connected, Loopback0
O 172.16.2.1/32 [110/65] via 192.168.1.2, 00:06:52, Serial0/0
C 192.168.1.0/24 is directly connected, Serial0/0
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
172.16.0.0/16 is variably subnetted, 3 subnets, 2 masks
O 172.16.1.1/32 [110/65] via 192.168.1.1, 00:06:52, Serial0/0
C 172.16.3.0/24 is directly connected, Loopback0
O 172.16.2.1/32 [110/65] via 192.168.1.2, 00:06:52, Serial0/0
C 192.168.1.0/24 is directly connected, Serial0/0
Finally, the ping results
R3#ping 172.16.1.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.16.1.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/28/80 ms
R3#ping 172.16.2.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.16.2.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/53/128 ms
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.16.1.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/28/80 ms
R3#ping 172.16.2.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.16.2.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/53/128 ms
That’s it. We solved the mystery of the non-broadcast ospf network type.
GNS3 topology and PT file
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