Today, I was practicing on OSPF and has come out with few questions while looking at the "debug ip ospf events" output. Here they are:-
Q1: What "Send immediate hello to nbr 0.0.0.254, src address 172.16.1.2, on FastEthernet0/0" implies? Why I can't see it through WireShark? Q2: Whenever neighbor change event is triggered DR BDR election takes place. However, in the below output I can see it took place contigiously two times, one after one. I have marked that in "RED". It happens even if there is only one new neigbor in the Neighbor field of Hello packet. Q3: Why one router waits for "Rcv DBD from 0.0.0.254 on FastEthernet0/0 seq 0x2BD opt 0x52 flag 0x7 len 32 mtu 1500 state INIT" from other router before being in 2-WAY state with that router. However. other router doesn't? I have higlighted it in "GREEN" below. Is this because, R3 has found R2 eligible by checking "Network Mask", "Area-ID", "Auth-type", Auth-key", but R2 just checked the "Neighbor" field and directly went to 2-WAY state without waiting for any DBDs. Confusing, DBDs are only sent after 2-WAYs. Q4: Why Negotiation is necessary in Broadcast and NBMA network, when we already know that DR has higher router-ID. Some times DR don't have higher router ID (if original DR gone down & then came back), but becomes SLAVE after negotiation. It creates confusion, can't DR be always MASTER? Q5: I thought router exchange LS-Request and LS-Update packets once they are in LOADING state. But I can see that it has started exchanging these packets even before the message "OSPF: Exchange Done with 0.0.0.254 on FastEthernet0/0". See in BLUE below. Why so? Q6: Lastly, I have seen first few LS-Update packets in WireShark. It's showing Type field as "STUB". But in later LS-Update packets, it got the right view of the network as "TRANSIT". Then why it got the wrong view of network first. What made it thought it was STUB at first place? ========================================= R3# *Mar 1 00:10:29.771: OSPF: Send hello to 224.0.0.5 area 0 on FastEthernet0/0 from 172.16.1.3 R3# *Mar 1 00:10:37.311: OSPF: Rcv hello from 0.0.0.254 area 0 from FastEthernet0/0 172.16.1.2 *Mar 1 00:10:37.315: OSPF: Send immediate hello to nbr 0.0.0.254, src address 172.16.1.2, on FastEthernet0/0 *Mar 1 00:10:37.319: OSPF: Send hello to 172.16.1.2 area 0 on FastEthernet0/0 from 172.16.1.3 *Mar 1 00:10:37.323: OSPF: End of hello processing R3# *Mar 1 00:10:39.771: OSPF: Send hello to 224.0.0.5 area 0 on FastEthernet0/0 from 172.16.1.3 **Mar 1 00:10:40.075: OSPF: Rcv DBD from 0.0.0.254 on FastEthernet0/0 seq 0x2BD opt 0x52 flag 0x7 len 32 mtu 1500 state INIT *Mar 1 00:10:40.075: OSPF: 2 Way Communication to 0.0.0.254 on FastEthernet0/0, state 2WAY **Mar 1 00:10:40.079: OSPF: Neighbor change Event on interface FastEthernet0/0 *Mar 1 00:10:40.079: OSPF: DR/BDR election on FastEthernet0/0 *Mar 1 00:10:40.083: OSPF: Elect BDR 0.0.0.254 *Mar 1 00:10:40.083: OSPF: Elect DR 0.0.0.255 *Mar 1 00:10:40.083: DR: 0.0.0.255 (Id) BDR: 0.0.0.254 (Id) *Mar 1 00:10:40.087: OSPF: Send DBD to 0.0.0.254 on FastEthernet0/0 seq 0x16AA opt 0x52 flag 0x7 len 32 *Mar 1 00:10:40.091: OSPF: First DBD and we are not SLAVE **Mar 1 00:10:40.095: OSPF: Rcv hello from 0.0.0.254 area 0 from FastEthernet0/0 172.16.1.2 *Mar 1 00:10:40.095: OSPF: Neighbor change Event on interface FastEthernet0/0 *Mar 1 00:10:40.099: OSPF: DR R3#/BDR election on FastEthernet0/0 *Mar 1 00:10:40.099: OSPF: Elect BDR 0.0.0.254 *Mar 1 00:10:40.103: OSPF: Elect DR 0.0.0.255 *Mar 1 00:10:40.103: DR: 0.0.0.255 (Id) BDR: 0.0.0.254 (Id) *Mar 1 00:10:40.107: OSPF: Neighbor change Event on interface FastEthernet0/0 *Mar 1 00:10:40.107: OSPF: DR/BDR election on FastEthernet0/0 *Mar 1 00:10:40.107: OSPF: Elect BDR 0.0.0.254 *Mar 1 00:10:40.111: OSPF: Elect DR 0.0.0.255 *Mar 1 00:10:40.111: DR: 0.0.0.255 (Id) BDR: 0.0.0.254 (Id) *Mar 1 00:10:40.115: OSPF: End of hello processing* *Mar 1 00:10:40.275: OSPF: Rcv DBD from 0.0.0.254 on FastEthernet0/0 seq 0x16AA opt 0x52 flag 0x2 len 52 mtu 1500 state EXSTART *Mar 1 00:10:40.275: OSPF: NBR Negotiation Done. We are the MASTER *Mar 1 00:10:40.279: OSPF: Send DBD to 0.0.0.254 on FastEthernet0/0 seq 0x16AB opt 0x52 flag 0x3 len 52 *Mar 1 00:10:40.347: OSPF: Rcv DBD from 0.0.0.254 on FastEthernet0/0 seq 0x16AB opt 0x52 flag 0x0 len 32 mtu 1500 state EX R3#CHANGE *Mar 1 00:10:40.351: OSPF: Send DBD to 0.0.0.254 on FastEthernet0/0 seq 0x16AC opt 0x52 flag 0x1 len 32 *Mar 1 00:10:40.355: OSPF: Send LS REQ to 0.0.0.254 length 12 LSA count 1 *Mar 1 00:10:40.479: OSPF: Rcv LS REQ from 0.0.0.254 on FastEthernet0/0 length 36 LSA count 1 *Mar 1 00:10:40.479: OSPF: Send UPD to 172.16.1.2 on FastEthernet0/0 length 40 LSA count 1 *Mar 1 00:10:40.479: OSPF: Rcv DBD from 0.0.0.254 on FastEthernet0/0 seq 0x16AC opt 0x52 flag 0x0 len 32 mtu 1500 state EXCHANGE **Mar 1 00:10:40.479: **OSPF: Exchange Done with 0.0.0.254 on FastEthernet0/0** **Mar 1 00:10:40.479: OSPF: Rcv LS UPD from 0.0.0.254 on FastEthernet0/0 length 64 LSA count 1 *Mar 1 00:10:40.479: OSPF: Synchronized with 0.0.0.254 on FastEthernet0/0, state FULL *Mar 1 00:10:40.483: %OSPF-5-ADJCHG: Process 100, Nbr 0.0.0.254 on FastEthernet0/0 from LOADING to FULL, Loading Done *Mar 1 00:10:41.159: OSPF: Rcv LS UPD from 0.0.0.254 on FastEthernet0/0 length 64 LSA count 1 *Mar 1 00: R3#10:41.167: OSPF: Rcv hello from 0.0.0.1 area 0 from FastEthernet0/0 172.16.1.1 *Mar 1 00:10:41.167: OSPF: Send immediate hello to nbr 0.0.0.1, src address 172.16.1.1, on FastEthernet0/0 *Mar 1 00:10:41.171: OSPF: Send hello to 172.16.1.1 area 0 on FastEthernet0/0 from 172.16.1.3 *Mar 1 00:10:41.175: OSPF: End of hello processing R3# *Mar 1 00:10:44.663: OSPF: Rcv hello from 0.0.0.254 area 0 from FastEthernet0/0 172.16.1.2 *Mar 1 00:10:44.667: OSPF: End of hello processing *Mar 1 00:10:45.455: OSPF: Rcv LS UPD from 0.0.0.254 on FastEthernet0/0 length 64 LSA count 1 R3# *Mar 1 00:10:46.295: OSPF: Rcv hello from 0.0.0.1 area 0 from FastEthernet0/0 172.16.1.1 *Mar 1 00:10:46.299: OSPF: Immediate hellos sent on FastEthernet0/0 limited by number non-full neighbors 1 *Mar 1 00:10:46.303: OSPF: End of hello processing R3# *Mar 1 00:10:49.771: OSPF: Send hello to 224.0.0.5 area 0 on FastEthernet0/0 from 172.16.1.3 *Mar 1 00:10:49.847: OSPF: Rcv DBD from 0.0.0.1 on FastEthernet0/0 seq 0x1DCC opt 0x52 flag 0x7 len 32 mtu 1500 state INIT *Mar 1 00:10:49.851: OSPF: 2 Way Communication to 0.0.0.1 on FastEthernet0/0, state 2WAY *Mar 1 00:10:49.855: OSPF: Neighbor change Event on interface FastEthernet0/0 *Mar 1 00:10:49.855: OSPF: DR/BDR election on FastEthernet0/0 *Mar 1 00:10:49.855: OSPF: Elect BDR 0.0.0.254 *Mar 1 00:10:49.859: OSPF: Elect DR 0.0.0.255 *Mar 1 00:10:49.859: DR: 0.0.0.255 (Id) BDR: 0.0.0.254 (Id) *Mar 1 00:10:49.863: OSPF: Send DBD to 0.0.0.1 on FastEthernet0/0 seq 0x131E opt 0x52 flag 0x7 len 32 *Mar 1 00:10:49.867: OSPF: First DBD and we are not SLAVE *Mar 1 00:10:49.943: OSPF: Rcv DBD from 0.0.0.1 on FastEthernet0/0 seq 0x131E opt 0x52 flag 0x2 len 112 mtu 1500 state EXSTART *Mar 1 00:10:49.947: OSPF: NBR Negotiation Done. We are the MASTER *Mar 1 0 R3#0:10:49.951: OSPF: Send DBD to 0.0.0.1 on FastEthernet0/0 seq 0x131F opt 0x52 flag 0x3 len 92 *Mar 1 00:10:50.043: OSPF: Rcv DBD from 0.0.0.1 on FastEthernet0/0 seq 0x131F opt 0x52 flag 0x0 len 32 mtu 1500 state EXCHANGE *Mar 1 00:10:50.047: OSPF: Send DBD to 0.0.0.1 on FastEthernet0/0 seq 0x1320 opt 0x52 flag 0x1 len 32 *Mar 1 00:10:50.051: OSPF: Send LS REQ to 0.0.0.1 length 12 LSA count 1 *Mar 1 00:10:50.091: OSPF: Rcv DBD from 0.0.0.1 on FastEthernet0/0 seq 0x1320 opt 0x52 flag 0x0 len 32 mtu 1500 state EXCHANGE *Mar 1 00:10:50.095: OSPF: Exchange Done with 0.0.0.1 on FastEthernet0/0 *Mar 1 00:10:50.115: OSPF: Rcv LS UPD from 0.0.0.1 on FastEthernet0/0 length 64 LSA count 1 *Mar 1 00:10:50.119: OSPF: Synchronized with 0.0.0.1 on FastEthernet0/0, state FULL *Mar 1 00:10:50.119: %OSPF-5-ADJCHG: Process 100, Nbr 0.0.0.1 on FastEthernet0/0 from LOADING to FULL, Loading Done R3# *Mar 1 00:10:52.163: OSPF: Rcv LS UPD from 0.0.0.1 on FastEthernet0/0 length 64 LSA count 1 R3# *Mar 1 00:10:53.247: OSPF: Rcv hello from 0.0.0.254 area 0 from FastEthernet0/0 172.16.1.2 *Mar 1 00:10:53.251: OSPF: End of hello processing R3# *Mar 1 00:10:55.203: OSPF: Rcv hello from 0.0.0.1 area 0 from FastEthernet0/0 172.16.1.1 *Mar 1 00:10:55.203: OSPF: Neighbor change Event on interface FastEthernet0/0 *Mar 1 00:10:55.203: OSPF: DR/BDR election on FastEthernet0/0 *Mar 1 00:10:55.203: OSPF: Elect BDR 0.0.0.254 *Mar 1 00:10:55.203: OSPF: Elect DR 0.0.0.255 *Mar 1 00:10:55.203: DR: 0.0.0.255 (Id) BDR: 0.0.0.254 (Id) *Mar 1 00:10:55.203: OSPF: End of hello processing R3# *Mar 1 00:10:59.771: OSPF: Send hello to 224.0.0.5 area 0 on FastEthernet0/0 from 172.16.1.3 R3# *Mar 1 00:11:02.467: OSPF: Rcv hello from 0.0.0.254 area 0 from FastEthernet0/0 172.16.1.2 *Mar 1 00:11:02.471: OSPF: End of hello processing R3# *Mar 1 00:11:04.391: OSPF: Rcv hello from 0.0.0.1 area 0 from FastEthernet0/0 172.16.1.1 *Mar 1 00:11:04.395: OSPF: End of hello processing R3# ===========================================================
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