OSPF has five types of packets, which have the same header format.

 OSPF Authentication Overview

TheAuth Typefield in the OSPF packet header determines the authentication mode. If theAuth Typeis 1, plaintext authentication is used.

Plaintext authentication involves transmitting the password in an easily readable format, which is less secure compared to MD5.

 HCIP-Datacom-Core Reference

Authentication mechanisms, including plaintext authentication, are detailed in the OSPF security configuration chapter, confirming thatAuth Type = 1corresponds to plaintext​​.