DBD (Database Description or Type2 OSPF Packet) is a sort of summary of the OSPF Database in a router. DBD is used to check if the LSDB between 2 routers is the same.
These packets are exchanged when an adjacency is being initialized. They describe the topology information a router has in its database. DBD uses poll-response procedure (master/slave). Master sends DBD packets/polls which are acknowledged by the slave.
Consider the simple below topology with two Routers:
As soon as we enable OSPF on the router interfaces, it starts exchanging Hello and DBD Packets.
It is obvious from the below detail, spend some time with it to understand it fully:
Good
DBD & LSU have same purpose?
As explained earlier, DBD (Database Description / Type2 OSPF Packet) is only a summary of the OSPF Database in a router. DBD is used to check if the LSDB between 2 routers is the same. It is not full packet.
LSU’s are full packets.
This example cleared Neighborship forming in my mind. Good!
Nice!!!
How neighborship formed in OSPF?
Let me explain this with an example.
Let’s say we have two routers R1 & R2.
R1’s router ID is 224.0.0.1 and R2’s router ID is 224.0.0.2.
R1 and R2 are connected via Ethernet but both are in DOWN STATE. When R1 is configured then it goes into INIT STATE.
R1 generates a statement “I’m router ID 224.0.0.1 and I see no one”.
When R2 comes into INIT STATE then R2 also generates a statement “I’m router ID 224.0.0.2, I see 224.0.0.1.
It is called 2-WAY-STATE.
Now both router store all information and neighbor neighborship is formed.
for more information please visit: https://aurumme.com/atech/ospf-type3-message-lsr-packet-link-state-request/
I had no clear idea how DBD works. Thanks for sharing the info?
thank you.