Reading the Output of 'debug ip ospf packet'

Using debug ip ospf packet we can look at the parameters in OSPF packets which is receiving from a neighbor..

Reading it's output by using the codes it uses may be helpful in deep troubleshooting.

Let's see a sample debug of a one packet..

Date and time is the time which the packet is received.
OSPF-100 PAK meaning a packet which belongs to OSPF process id 100
rcv means received packet
v:2 means OSPF version is 2
t:1 means the OSPF packet type is 1
     Following are the packet types by it's number..
     1. Hello
     2. DBD (Database Discription)
     3. LSR (Link State Request)
     4. LSU (Link State Update)
     5. LSAck (Link State Ack)
l:48 means the packet length in bytes (this packet is 48 bytes)
rid:2.2.2.2 means the router-id of the packet sender
aid:0.0.0.0 means the area-id is 0
chk:4D40 is the checksum which is used to validate the packet
aut:0 means the authentication is none
         if aut:1 it means the authentication is plain text
         if aut:2 it means the authentication is MD5 digest
auk: will show some more details like the key-id and sequence if authentication is enabled
from Ethernet0/0 is the interface which the packet is received

OSPF Neighbor States Changing on 'debug ip ospf adj'

debug ip ospf adj is used to troubleshoot neighbor adjacency issues of OSPF. It lists all the state changes a router go through when forming a neighbor relationship.

As a summary it should go through the following states.

1. Down: no OSPF neighbors detected at this moment.
2. Init: Hello packet received.
3. Two-way: own router ID found in received hello packet.
4. ExStart: master and slave roles determined.
5. Exchange: database description packets (DBD) are sent.
6. Loading: exchange of LSRs (Link state request) and LSUs (Link state update) packets.
7. Full: OSPF routers now have an adjacency.

Let's see how it is displayed on a router. Only two routers are connected for this lab with a direct cable and following configuration is applied to both routers. Note that the link is a multi access segment with a /24 subnet.

Router(config)#router ospf 100
Router(config-router)#network 192.168.12.0 0.0.0.255 area 0

R1's interface is 192.168.12.1/24 and R2's interface is 192.168.12.2/24
R1's loopback is 1.1.1.1/32 and R2's loopback is 2.2.2.2/32

(click on the images to view in full size)