I noticed a bogus entry in the arp table:

# cat /proc/net/arp
IP address       HW type     Flags       HW address            Mask     Device   0x1         0x2         00:15:XX:XX:XX:5B     *        br0  0x1         0x0         00:19:XX:XX:XX:56     *        br0    0x1         0x2         00:14:XX:XX:XX:CD     *        vlan1 was a laptop connected a few days ago, and its entry is still there.
Also, what is the meaning of flag value 0x0 ?

I tried "ip neigh flush dev br0" and also " ip neigh del to lladdr 00:19:XX:XX:XX:56  dev br0", but neither did any change.
Is there a version of the arp command that supports the -d option?