The use of type 0 indicates that VRRP advertisement messages are not authenticated (provides no authentication). The master transmitting VRRP advertisement messages will transmit the value 0 in the egress messages authentication type field and the authentication data field. Backup virtual routers receiving VRRP advertisement messages with the authentication type field equal to 0 will ignore the authentication data field in the message.
All compliant VRRP advertisement messages are accepted. The following fields within the received VRRP advertisement message are checked for compliance (the VRRP specification may require additional checks):
IP header checks specific to VRRP:
IP header destination IP address - must be 224.0.0.18
IP header TTL field - must be equal to 255, the packet must not have traversed any IP routed hops
IP header protocol field - must be 112 (decimal)
VRRP message checks:
Version field
Must be set to the value 2.
Type field
Must be set to the value of 1 (advertisement).
Virtual router ID field
Must match one of the configured VRID on the ingress IP interface (All other fields are dependent on matching the virtual router ID field to one of the interfaces configured VRID parameters).
Priority field
Must be equal to or greater than the VRID in-use priority or be equal to 0 (Note, equal to the VRID in-use priority and 0 requires further processing regarding master/backup and senders IP address to determine the validity of the message).
Authentication type field
Must be equal to 0.
Advertisement interval field
Must be equal to the VRID configured advertisement interval.
Checksum field
Must be valid
Authentication data fields
Must be ignored.
VRRP messages not meeting the criteria are silently dropped.