The authentication method used for VRRP protocol exchanges on this virtual router: noAuthentication(1, the default), simpleTextPassword(2), or ipAuthenticationHeader(3); the value is shared across all VRRP instances on the same ifIndex. Admins set simpleTextPassword or the IP auth header when they want to prevent unauthorized routers from joining or disrupting the VRRP group, though modern deployments increasingly rely on physical/VLAN segmentation instead since these mechanisms are considered legacy.