OSPF Adjacencies in point to point

Routing & Switching OSPF
1

Hi Rene,

I have a doubt. Whether 2-way state is present in point to point network type?

//Sudha

2

Hello @sudha.sairam19,

Yes, all network types will have the 2-way state. Let’s bring the live equipment, shall we?
image
Here I have two routers (R4 and R5) connected together via serial links. I will just enable ospf on them and turn on the debug to watch the neighbor adjacency states in action.

R4:    
    interface Serial2/0
     ip address 192.168.45.4 255.255.255.0          
     clock rate 128000
     no shut

R5:
interface Serial2/0
 ip address 192.168.45.5 255.255.255.0
 no sh

**Enabling ospf on both: (I will turn on debugs before doing this- otherwise I won't see the cool stuff)**

router ospf 1
 log-adjacency-changes
 network 192.168.45.0 0.0.0.255 area 0

I know we know but let’s verify the network type:

R4#show ip ospf int s2/0 | i Netw
  Process ID 1, Router ID 192.168.45.4, Network Type POINT_TO_POINT, Cost: 64

R5#show ip ospf int s2/0 | i Net
  Process ID 1, Router ID 192.168.45.5, Network Type POINT_TO_POINT, Cost: 64

Let’s check the debugs:

OSPF: Send hello to 224.0.0.5 area 0 on Serial2/0 from 192.168.45.5
OSPF: Rcv hello from 192.168.45.4 area 0 from Serial2/0 192.168.45.4
OSPF: Send immediate hello to nbr 192.168.45.4, src address 192.168.45.4, on Serial2/0
OSPF: Send hello to 224.0.0.5 area 0 on Serial2/0 from 192.168.45.5
OSPF: End of hello processing
 OSPF: Rcv hello from 192.168.45.4 area 0 from Serial2/0 192.168.45.4

OSPF: 2 Way Communication to 192.168.45.4 on Serial2/0, state 2WAY

OSPF: Serial2/0 Nbr 192.168.45.4: Prepare dbase exchange
OSPF: Send DBD to 192.168.45.4 on Serial2/0 seq 0x1B84 opt 0x52 flag 0x7 len 32
OSPF: End of hello processing

 OSPF: Rcv DBD from 192.168.45.4 on Serial2/0 seq 0x28A opt 0x52 flag 0x7 len 32  mtu 1500 state EXSTART
 OSPF: First DBD and we are not SLAVE
OSPF: Rcv DBD from 192.168.45.4 on Serial2/0 seq 0x1B84 opt 0x52 flag 0x2 len 52  mtu 1500 state EXSTART
 OSPF: NBR Negotiation Done. We are the MASTER
 OSPF: Serial2/0 Nbr 192.168.45.4: Summary list built, size 1
 OSPF: Send DBD to 192.168.45.4 on Serial2/0 seq 0x1B85 opt 0x52 flag 0x1 len 52
 OSPF: Rcv LS REQ from 192.168.45.4 on Serial2/0 length 36 LSA count 1
 OSPF: Send UPD to 192.168.45.4 on Serial2/0 length 40 LSA count 1

 OSPF: Rcv DBD from 192.168.45.4 on Serial2/0 seq 0x1B85 opt 0x52 flag 0x0 len 32  mtu 1500 state EXCHANGE
 OSPF: Exchange Done with 192.168.45.4 on Serial2/0
 OSPF: Send LS REQ to 192.168.45.4 length 12 LSA count 1
 OSPF: Rcv LS UPD from 192.168.45.4 on Serial2/0 length 52 LSA count 1

 OSPF: Synchronized with 192.168.45.4 on Serial2/0, state FULL

%OSPF-5-ADJCHG: Process 1, Nbr 192.168.45.4 on Serial2/0 from LOADING to FULL, Loading Done

As you can see the 2-way state is happening on point to point and that’s when a router will see it’s own router ID within the hello packet from the neighbor which means bi-directional communication has been established between two routers.

Regards.

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