OSPF has five types of packets, which have the same header format. If the Auth Type field in the packet header is 1, which of the following authentication modes is used?

The OSPF packet header contains a 16-bit Auth Type field that specifies the authentication method used. According to the OSPFv2 standard defined in RFC 2328, the values for this field are standardized. An Auth Type value of 1 explicitly indicates the use of "Simple password" authentication, also known as plaintext authentication. In this mode, an 8-octet password is included directly in the packet's authentication field in clear text. While simple to configure, it is considered insecure as the password can be easily captured.

A. Non-authentication: This mode, where no authentication is performed, is indicated by an Auth Type value of 0.
B. MD5 authentication: This is a form of cryptographic authentication, which is specified by an Auth Type value of 2.
D. Hash authentication: This is a general category. The specific OSPF cryptographic authentication (which uses hashing like MD5) is assigned the Auth Type value 2.

1. Moy

J. (1998). RFC 2328: OSPF Version 2. The Internet Society. Appendix D.3

"The OSPF packet header". This document defines the Auth Type field values

stating: "1 - Simple password".

2. Huawei. (2020). HCIP-Datacom-Core Technology V1.0 Training Material. Section: OSPF Principles

Subsection: OSPF Authentication. This official courseware details the OSPF packet header

confirming that an Auth Type of 1 corresponds to simple (plaintext) authentication.

3. Kurose

J. F.

& Ross

K. W. (2021). Computer Networking: A Top-Down Approach (8th ed.). Pearson. Chapter 5.2

"The Link-State (LS) Routing Algorithm". The section on OSPF describes its packet format and authentication types

aligning with the RFC 2328 standard where type 1 is simple password.