How does IPVS sync connection info from master to backup?

Issue

• How does IPVS sync connection info from master to backup?

man page KEEPALIVED.CONF(5):

        lvs_sync_daemon <INTERFACE> <VRRP_INSTANCE> [id <SYNC_ID>] [maxlen <LEN>] [port <PORT>] [ttl <TTL>] [group <IP ADDR>]
                                     # Binding interface, vrrp instance and optional
                                     #  syncid for lvs syncd
                                     #  syncid (0 to 255) for lvs syncd
                                     #  maxlen (1..65507) maximum packet length
                                     #  port (1..65535) UDP port number to use
                                     #  ttl (1..255)
                                     #  group - multicast group address (IPv4 or IPv6)
                                     # NOTE: maxlen, port, ttl and group are only available on Linux 4.3 or later.