OSPF DBD (Database Descriptor) Packets: OSPF Packet Types

Rashmi Bhardwaj | Blog,Routing & Switching

Introduction to OSPF DBD

IP routing is the most important aspect of networking. There are several types of protocols which support IP routing using distance vector mechanism or link state mechanism. Ultimate goal of IP routing is to find the best shortest path for packet delivery in the network. Link state routing protocols are more commonly and widely used as they support large enterprises, IPv4, IPv6 networks, CIDR and VLSM addressing models. Some routing protocols use transport protocols such as TCP and UDP for data transmission, however protocols such as Open Shortest path first (OSPF) will not carry data using TCP and UDP.

Today we look more in detail about OSPF DBD (database descriptor) packet type, its purpose, working and features.

OSPF DBD packets

Download the OSPF DBD Packet Cheatsheet


Also Refer: OSPF Packet Types: The Ultimate Guide

OSPF Database Descriptor (DBD) Packet: Working & Features 

The link state routing protocols required their link state database should remain synchronized across all routers to function properly. The synchronization starts as soon as adjacency is performed between neighbouring routers. The OSPF uses a database descriptor (DBD) packet to achieve this purpose. The database comprises multiple packets. The poll response procedure is used to describe multiple packet usage. The routers are designated as Master and slaves. Database description is sent by slave router after master sends the database description packet. 

  • OSPF router performs summarization of database descriptor (DBD) packets and LSA set belongs to that database.
  • When the neighbour views LSA , having a more recent copy of its own database, it requests a new LSA from the neighbour.
  • Routers holding LSA do not send packets immediately after hearing hello and parameter check; instead each router will create and send the database descriptor (DBD) packets which contain each LSA header.
  • The header includes information for unique identification of LSA and the revision.
  • The DD message will use OSPF defined simple error recovery process. Each DD packet has several LSA headers, with an assigned sequence number.
  • The receiver acknowledgement happens for received DD packets by sending DD packets with the same sequence number.
  • Sender will use a window size of 1 packet before sending the next DD packet and wait for acknowledgement.
  • As the relationship between two routers is formed by neighbours it determines which router will be master and which router will be slave during the exchange of database.
  • During DD packet exchange the role of master and slave determine routers responsibilities. The LSA header has a local router database.
  • DD sequence number is used to sequentially arrange database descriptor (DBD) packet collection. The sequence number increments by 1 until the overall database description is sent. 
  • Interface MTU is having MTU value of outgoing interface. For virtual fields this value is set to 0x0000. 

A typical OSPF DBD (database descriptor) Packet

A typical OSPF DBD packet looks like as under:

Open Shortest path first 

   OSPF header 

   OSPF version : 2

    Message type: DB Descr. (2) 

    Packet length : 72 

    Source OSPF router : ( 

    Area ID: (backbone)

    Packet checksum :0x9d6b

    Auth type: null

 OSPF DBD (database description)

   Interface MTU: 1500

   Options: 0x52 (O,L,E) 

      DB description: 0x03 (M,MS) 

       ………….0…. = R: OOBResync bit not set 

       ………….0…. = I: Init bit not set 

       ………….1…. = M: More bit set

       ………….1…. = MS: Master/Slave bit set 

  DD sequence : 9755 

 LSA header 

  LS age : 972 seconds

  Do not age: False

  Options: 0x22 (DC,E)

   Link-state advertisement type: Router-LSA (1)

   Link-state ID :

   Advertising router: ( 

   LS sequence number: 0x8000002a

   LS checksum: 0xc970

   Length: 48 

LSA header 

LS age : 11 seconds

  Do not age: False

  Options: 0x22 (DC,E)

   Link-state advertisement type: Router-LSA (1)

   Link-state ID :

   Advertising router: ( 

   LS sequence number: 0x80000031

   LS checksum: 0xc9948

   Length: 36

Continue Reading:

EIGRP Packet Types: The Complete Guide

OSPF Router Types: Detailed Explanation

Are you preparing for your next interview?

If you want to learn more about OSPF, then check our e-book on OSPF Interview Questions and Answers in easy to understand PDF Format explained with relevant Diagrams (where required) for better ease of understanding.


Leave a Comment

Your email address will not be published. Required fields are marked *

Shopping Cart