Type. 8 bits.
OSPF request/reply code.

Length. 16 bits.
Size of the OSPF message including the OSPF header in bytes.

Router ID. 32 bits.
The Router ID of the packet's source.

Area ID. 32 bits.
The area that this packet belongs to. All OSPF packets are associated with a single area. Most travel a single hop only. Packets travelling over a virtual link are labelled with the backbone Area ID of 0.0.0.0.

Checksum. 16 bits.
The standard IP checksum of the entire contents of the packet, starting with the OSPF packet header but excluding the 64 bit authentication field. This checksum is calculated as the 16-bit one's complement of the one's complement sum of all the 16 bit words in the packet, excepting the authentication field. If the packet's length is not an integral number of 16 bit words, the packet is padded with a byte of zero before checksumming. The checksum is considered to be part of the packet authentication procedure; for some authentication types the checksum calculation is omitted.

AuType. 16 bits.
Identifies the authentication procedure to be used for the packet.

Authentication. 64 bits.