OSPF Packet Type

OSPF uses multiple OSPF packets to perform more advanced operations than RIP. OSPF packets are encapsulated in IP and exchanged between routers. The protocol number in the IP header is 89. The OSPF packets exchanged by OSPF routers are of the following types

Figure OSPF packet encapsulation
Figure OSPF packet encapsulation
Type Packet type
1 Hello
2 DD(Database Description)
3 LSR(Link State Request)
4 LSU(Link State Update)
5 LSAck(Link State Acknowledgement)
Table OSPF Packet Type

Hello packet

Hello packets are used for dynamic discovery and maintaining of neighbors.

Related article

The details of Hello Packet are explained in the following article.

N-Study
OSPF Hello Packet | N-Study
https://www.n-study.com/en/ospf-detail/ospf-hello/
OSPF Hello packets are used to establish OSPF neighbors; this section details the format of OSPF Hello packets and the conditions for establishing a neighbor.

DD packet

DD packets are used to synchronize the link state database; they contain the LSA header part contained in their own LSDB.

DBD is sometimes used as an abbreviation for DD.

Related article

Details of DD packets are explained in the following article.

N-Study
OSPF DD(Database Description) Packet | N-Study
https://www.n-study.com/en/ospf-detail/ospf-dd/
OSPF DD packets are packets that provide an overview of LSDB. the format of DD packets is explained.

LSR packet

LSR packets are packets that request the missing LSAs recognized in the exchange of DD packets.

LSU packet

The LSU packet sends the LSA requested by the LSR. LSU packets contain LSAs.

LSAck packet

LSAck packets are used to confirm the reception of LSU packets.

OSPF header format

The format of the 24-byte OSPF header that is commonly added to OSPF packets is as follows

Figure OSPF header format

Version

Version (8 bits) is the OSPF version; the OSPF version for IPv4 is “2”.

Type

The Type (8 bits) indicates the type of OSPF packet as described above.

Packet Length

Packet Length (16 bits) is the combined length of the OSPF header and the OSPF data portion.

Router ID

The Router ID (32-bit) is a 32-bit identification number that identifies an OSPF router.

Related article

For more information about OSPF router IDs, please see the following article

N-Study
OSPF Router ID : Identify OSPF routers | N-Study
https://www.n-study.com/en/ospf-detail/router-id/
The router ID is a 32-bit number that identifies the OSPF router. Just like IPv4 addresses, it's an 8-bit decimal number separated by ". (dot)" and then write four of them in a row.

Area ID

Area ID (32 bits) is the area number to which the OSPF enabled interface belongs.

Checksum

Checksum (16 bits) to perform error checking.

AuType

AuType (16 bits) indicates the type of authentication.

AuType value Type of authentication
0 No authentication
1 plaintext password
2 MD5

Authentication

Authentication (64 bit) is the data used for authentication.

How the OSPF works