Keepalived VIP for k8s

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Cluster information:

Kubernetes version:1.21.6
Cloud being used: VPC
Installation method:yum
Host OS: centos7.9
CNI and version:default
CRI and version: defalut
network plugin:flannel 0.15
keepalived version:1.3.5
kube-proxy mode:ipvs

I have a http service with nodePort 30080, i config keepalived VIP as :192.168.20.200/24 brd 192.168.20.255 dev eth0 label eth0:vip, when node is get VIP, but ipvsadm -ln | grep 30080, the 192.168.20.180 is not in the ipvs forward table, but the ipaddr for eth0 192.168.20.51/24 is in the ipvs table; if i change the VIP to 192.168.20.180/25(is not same to 24 well), it work correct, why? please help me, tks a lot.