Refer to Exhibit:All of the switches in the exhibit are AOS-CX switches.

Why MD5 Authentication on Lag 1 is Preferred:

Lag 1 is the primary link between Switch-2 and Switch-1, both of which are Layer 3 switches running OSPF.

By enabling MD5 authentication, OSPF routers exchange authenticated packets, preventing unauthorized or rogue OSPF routers from forming adjacencies or injecting routes.

MD5 is a secure authentication method and ensures the integrity and authenticity of OSPF communications.

Other Options Analysis:

A. Configure OSPF authentication on VLANs 10-19 in password mode: While configuring authentication on VLAN interfaces could secure VLAN-specific OSPF traffic, it is less effective because the main threat of rogue OSPF comes from unauthorized L3 devices connected via the backbone (Lag 1).

C. Disable OSPF entirely on VLANs 10-19: Disabling OSPF on these VLANs is not a preferred solution because OSPF is needed to route traffic in this design.

D. Configure passive-interface as the OSPF default and disable OSPF passive on Lag 1: While passive interfaces prevent OSPF from forming adjacencies, it does not directly prevent rogue routers. Passive mode only limits OSPF advertisements on specific interfaces.