How to Flush ARP cache in Windows, Linux and MacOS

With certain network changes you might end up with nodes in your network having issues contacting other hosts outside of their subnet.

A typical scenario is when the default gateway's IP is re-assigned to a new router and the old device stays up for some reason. Hosts, that contacted the old router earlier know it's MAC address and associate the old IP with that MAC. However, the IP belongs to a different node now, so these network hosts will have connectivity issues outside of their subnet.

A quick fix is flushing the ARP cache on these hosts, so they can query and learn the MAC address of the new router.

Flush the ARP cache - Windows

Flushing the ARP cache on a Windows machine is easy: use the arp -d command.

# View the ARP table
arp -a 

# Delete a single entry (1.1.1.1 in this example)
arp -d 1.1.1.1

# Flush the whole ARP cache
arp -d *
# *** or ***
arp -a -d

Flush the ARP cache - Linux

The syntax is a little different on Unix type systems:

# View the ARP cache
arp -n 

# Delete a single entry (1.1.1.1 here)
arp -d 1.1.1.1

# Flush the whole cache
ip -s neigh flush all

Flush the ARP cache - Mac

# View the ARP cache
arp -a

# Delete a single entry (1.1.1.1 in this example)
sudo arp -d 1.1.1.1

# Flush the whole ARP cache
sudo arp -a -d