Read-create selector (default noAuthentication) for how VRRP protocol exchanges between virtual routers are authenticated: no authentication, a clear-text simple password, or an IP authentication header; per the RFC, this value must match across all routers sharing the same ifIndex/VRID. Admins set simpleTextPassword or ipAuthenticationHeader to prevent a rogue device from injecting VRRP advertisements and hijacking the virtual router role, though these older mechanisms provide only weak protection by modern standards.