ip neigh add 192.168.1.5 lladdr aa:bb:cc:dd:ee:ff dev eth0
Manually insert a static neighbor entry
This pins the MAC address aa:bb:cc:dd:ee:ff to IP 192.168.1.5 in the kernel's neighbor cache, bypassing ARP for that host. Use it when a device answers ARP unreliably or for security on a trusted wired segment. The entry is temporary and vanishes on reboot, and newer kernels may want nud permanent appended to keep it from expiring.
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