OSPF Network Type – Non-Broadcast

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Points to remember about Non-Broadcast OSPF network type.

1. Designated Router (DR) and Back Designated Router(BDR) election occurs. BDR sends LS to multicast address 224.0.0.6 which is the DR and DR sends LS to multicast address 224.0.0.5 which is all routers within the area.
2. No pre-emption meaning when the DR goes down, BDR takes DR responsibility but when DR comes backup it won’t become the DR.
3. DR/BDR election process is based on the following criterias:
3a. Highest Router ID (RID)
3b. Highest IP address assigned on a loopback interface
3c. Highest IP address assigned on a non-loopback (physical) interface
4. Default network type on non-broadcast media like Frame Relay, ATM and X.25.
5. OSPF hello is exchange as unicast (neighbor statement under the OSPF process).

             Spoke                   Spoke
           .-----.                 .-----.
           | R01 |---.        .----| R02 |
           '-----'   |        |    '-----'
                     |        |
                S0/0 |        | S0/0
                .1   v        v .2  
                 .------------------.
                / Frame Relay Switch \
               (     10.0.0.0/24      )
                \                    /
                 '------------------'
                           ^
                           | .3   
                           | S0/0 
                        .-----.
                        | R03 |
                        '-----'
                          Hub 

Once the neighbor statements have been configured under the OSPF process, R03 attempts to form adjaceny by sending OSPF hello.

R3(config-router)#neighbor 10.0.0.1 
R3(config-router)#neighbor 10.0.0.2
R3(config-router)#
*Mar  1 00:06:46.091: OSPF: Starting 0.0.0.0 address 10.0.0.1 on Serial0/0
*Mar  1 00:06:47.023: OSPF: Starting 0.0.0.0 address 10.0.0.2 on Serial0/0

R3#sh ip ospf neighbor 

Neighbor ID     Pri   State           Dead Time   Address         Interface
N/A               0   ATTEMPT/DROTHER 00:01:55    10.0.0.1        Serial0/0
N/A               0   ATTEMPT/DROTHER 00:01:56    10.0.0.2        Serial0/0

DR/BDR election starts. R03 becomes the DR as it has the highest Router ID and R02 becomes the BDR as it has the second highest Router ID.

*Mar  1 00:06:50.423: OSPF: 2 Way Communication to 2.2.2.2 on Serial0/0, state 2WAY
*Mar  1 00:06:50.423: OSPF: Neighbor change Event on interface Serial0/0
*Mar  1 00:06:50.423: OSPF: DR/BDR election on Serial0/0 
*Mar  1 00:06:50.423: OSPF: Elect BDR 0.0.0.0
*Mar  1 00:06:50.423: OSPF: Elect DR 3.3.3.3
*Mar  1 00:06:50.423:        DR: 3.3.3.3 (Id)   BDR: none 
*Mar  1 00:06:50.427: OSPF: Send DBD to 2.2.2.2 on Serial0/0 seq 0x1450 opt 0x52 flag 0x7 len 32
*Mar  1 00:06:50.427: OSPF: Neighbor change Event on interface Serial0/0
*Mar  1 00:06:50.427: OSPF: DR/BDR election on Serial0/0 
*Mar  1 00:06:50.427: OSPF: Elect BDR 0.0.0.0
*Mar  1 00:06:50.431: OSPF: Elect DR 3.3.3.3
*Mar  1 00:06:50.431:        DR: 3.3.3.3 (Id)   BDR: none 
*Mar  1 00:06:50.435: OSPF: 2 Way Communication to 1.1.1.1 on Serial0/0, state 2WAY
*Mar  1 00:06:50.435: OSPF: Neighbor change Event on interface Serial0/0
*Mar  1 00:06:50.435: OSPF: DR/BDR election on Serial0/0 
*Mar  1 00:06:50.435: OSPF: Elect BDR 0.0.0.0
*Mar  1 00:06:50.435: OSPF: Elect DR 3.3.3.3
*Mar  1 00:06:50.435:        DR: 3.3.3.3 (Id)   BDR: none 
*Mar  1 00:06:50.435: OSPF: Send DBD to 1.1.1.1 on Serial0/0 seq 0x1C2B opt 0x52 flag 0x7 len 32
*Mar  1 00:06:50.435: OSPF: Neighbor change Event on interface Serial0/0
*Mar  1 00:06:50.435: OSPF: DR/BDR election on Serial0/0 
*Mar  1 00:06:50.435: OSPF: Elect BDR 0.0.0.0
*Mar  1 00:06:50.435: OSPF: Elect DR 3.3.3.3
*Mar  1 00:06:50.435:        DR: 3.3.3.3 (Id)   BDR: none 
*Mar  1 00:06:50.439: OSPF: Rcv DBD from 2.2.2.2 on Serial0/0 seq 0x2384 opt 0x52 flag 0x7 len 32  mtu 1500 state EXSTART
*Mar  1 00:06:50.439: OSPF: First DBD and we are not SLAVE
*Mar  1 00:06:50.439: OSPF: Rcv DBD from 2.2.2.2 on Serial0/0 seq 0x1450 opt 0x52 flag 0x2 len 52  mtu 1500 state EXSTART
*Mar  1 00:06:50.439: OSPF: NBR Negotiation Done. We are the MASTER
*Mar  1 00:06:50.439: OSPF: Send DBD to 2.2.2.2 on Serial0/0 seq 0x1451 opt 0x52 flag 0x3 len 52
*Mar  1 00:06:50.439: OSPF: Rcv DBD from 1.1.1.1 on Serial0/0 seq 0x2189 opt 0x52 flag 0x7 len 32  mtu 1500 state EXSTART
*Mar  1 00:06:50.439: OSPF: First DBD and we are not SLAVE
*Mar  1 00:06:50.439: OSPF: Rcv DBD from 1.1.1.1 on Serial0/0 seq 0x1C2B opt 0x52 flag 0x2 len 52  mtu 1500 state EXSTART
*Mar  1 00:06:50.439: OSPF: NBR Negotiation Done. We are the MASTER
*Mar  1 00:06:50.439: OSPF: Send DBD to 1.1.1.1 on Serial0/0 seq 0x1C2C opt 0x52 flag 0x3 len 52
*Mar  1 00:06:50.443: OSPF: Rcv DBD from 2.2.2.2 on Serial0/0 seq 0x1451 opt 0x52 flag 0x0 len 32 mtu 1500 state EXCHANGE
*Mar  1 00:06:50.443: OSPF: Send DBD to 2.2.2.2 on Serial0/0 seq 0x1452 opt 0x52 flag 0x1 len 32
*Mar  1 00:06:50.443: OSPF: Send LS REQ to 2.2.2.2 length 12 LSA count 1
*Mar  1 00:06:50.443: OSPF: Rcv DBD from 1.1.1.1 on Serial0/0 seq 0x1C2C opt 0x52 flag 0x0 len 32  mtu 1500 state EXCHANGE
*Mar  1 00:06:50.443: OSPF: Send DBD to 1.1.1.1 on Serial0/0 seq 0x1C2D opt 0x52 flag 0x1 len 32
*Mar  1 00:06:50.443: OSPF: Send LS REQ to 1.1.1.1 length 12 LSA count 1
*Mar  1 00:06:50.443: OSPF: Rcv LS REQ from 2.2.2.2 on Serial0/0 length 36 LSA count 1
*Mar  1 00:06:50.443: OSPF: Send UPD to 10.0.0.2 on Serial0/0 length 40 LSA count 1
*Mar  1 00:06:50.447: OSPF: Rcv DBD from 2.2.2.2 on Serial0/0 seq 0x1452 opt 0x52 flag 0x0 len 32  mtu 1500 state EXCHANGE
*Mar  1 00:06:50.447: OSPF: Exchange Done with 2.2.2.2 on Serial0/0
*Mar  1 00:06:50.447: OSPF: Rcv LS UPD from 2.2.2.2 on Serial0/0 length 64 LSA count 1
*Mar  1 00:06:50.447: OSPF: Synchronized with 2.2.2.2 on Serial0/0, state FULL
*Mar  1 00:06:50.447: %OSPF-5-ADJCHG: Process 1, Nbr 2.2.2.2 on Serial0/0 from LOADING to FULL, Loading Done
*Mar  1 00:06:50.451: OSPF: Rcv LS REQ from 1.1.1.1 on Serial0/0 length 36 LSA count 1
*Mar  1 00:06:50.451: OSPF: Send UPD to 10.0.0.1 on Serial0/0 length 40 LSA count 1
*Mar  1 00:06:50.451: OSPF: Rcv DBD from 1.1.1.1 on Serial0/0 seq 0x1C2D opt 0x52 flag 0x0 len 32  mtu 1500 state EXCHANGE
*Mar  1 00:06:50.451: OSPF: Exchange Done with 1.1.1.1 on Serial0/0
*Mar  1 00:06:50.451: OSPF: Rcv LS UPD from 1.1.1.1 on Serial0/0 length 64 LSA count 1
*Mar  1 00:06:50.451: OSPF: Synchronized with 1.1.1.1 on Serial0/0, state FULL
*Mar  1 00:06:50.451: %OSPF-5-ADJCHG: Process 1, Nbr 1.1.1.1 on Serial0/0 from LOADING to FULL, Loading Done
*Mar  1 00:06:50.927: OSPF: Build router LSA for area 0, router ID 3.3.3.3, seq 0x80000002
*Mar  1 00:06:50.939: OSPF: Rcv LS UPD from 2.2.2.2 on Serial0/0 length 64 LSA count 1
*Mar  1 00:06:50.943: OSPF: Rcv LS UPD from 1.1.1.1 on Serial0/0 length 64 LSA count 1
*Mar  1 00:06:50.947: OSPF: Build network LSA for Serial0/0, router ID 3.3.3.3
*Mar  1 00:06:50.947: OSPF: Build network LSA for Serial0/0, router ID 3.3.3.3
*Mar  1 00:06:55.915: OSPF: Neighbor change Event on interface Serial0/0
*Mar  1 00:06:55.915: OSPF: DR/BDR election on Serial0/0 
*Mar  1 00:06:55.919: OSPF: Elect BDR 2.2.2.2
*Mar  1 00:06:55.919: OSPF: Elect DR 3.3.3.3
*Mar  1 00:06:55.919:        DR: 3.3.3.3 (Id)   BDR: 2.2.2.2 (Id)
*Mar  1 00:06:55.919: OSPF: Neighbor change Event on interface Serial0/0
*Mar  1 00:06:55.919: OSPF: DR/BDR election on Serial0/0 
*Mar  1 00:06:55.919: OSPF: Elect BDR 2.2.2.2
*Mar  1 00:06:55.919: OSPF: Elect DR 3.3.3.3
*Mar  1 00:06:55.919:        DR: 3.3.3.3 (Id)   BDR: 2.2.2.2 (Id)
*Mar  1 00:06:57.143: OSPF: Neighbor change Event on interface Serial0/0
*Mar  1 00:06:57.143: OSPF: DR/BDR election on Serial0/0 
*Mar  1 00:06:57.147: OSPF: Elect BDR 2.2.2.2
*Mar  1 00:06:57.147: OSPF: Elect DR 3.3.3.3
*Mar  1 00:06:57.147:        DR: 3.3.3.3 (Id)   BDR: 2.2.2.2 (Id)
*Mar  1 00:06:57.147: OSPF: Neighbor change Event on interface Serial0/0
*Mar  1 00:06:57.147: OSPF: DR/BDR election on Serial0/0 
*Mar  1 00:06:57.147: OSPF: Elect BDR 2.2.2.2
*Mar  1 00:06:57.151: OSPF: Elect DR 3.3.3.3
*Mar  1 00:06:57.151:        DR: 3.3.3.3 (Id)   BDR: 2.2.2.2 (Id)

OSPF neighbor from R03’s perspective.

R3#sh ip ospf ne

Neighbor ID     Pri   State           Dead Time   Address         Interface
1.1.1.1           1   FULL/DROTHER    00:01:50    10.0.0.1        Serial0/0
2.2.2.2           1   FULL/BDR        00:01:48    10.0.0.2        Serial0/0

The command “show IP ospf interface” shows all the interface running OSPF. The output displays important information like network type, hello intervals including dead, wait and retransmits and DR/BDR.

R3#sh ip ospf interface
Serial0/0 is up, line protocol is up 
  Internet Address 10.0.0.3/24, Area 0 
  Process ID 1, Router ID 3.3.3.3, Network Type NON_BROADCAST, Cost: 64
  Enabled by interface config, including secondary ip addresses
  Transmit Delay is 1 sec, State DR, Priority 1 
  Designated Router (ID) 3.3.3.3, Interface address 10.0.0.3
  Backup Designated router (ID) 2.2.2.2, Interface address 10.0.0.2
  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 1/1, flood queue length 0
  Next 0x0(0)/0x0(0)
  Last flood scan length is 3, maximum is 3
  Last flood scan time is 0 msec, maximum is 0 msec
  Neighbor Count is 2, Adjacent neighbor count is 2 
    Adjacent with neighbor 1.1.1.1
    Adjacent with neighbor 2.2.2.2  (Backup Designated Router)
  Suppress hello for 0 neighbor(s)

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