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answered 2021-06-07 16:17:25 +0000

Chuckc gravatar image

arp -a is a passive action showing the contents of the local ARP cache.

You can use arp -d to remove individual entries or the whole cache with arp -d *
If there is no entry in the cache, then something needing to access a local (on same subnet) IP address (like ping) will force an ARP request.
In the example below there is only one interface. The subnet is determined from the Default Gateway and Subnet Mask.

arp -d will require Admin permissions.

https://docs.microsoft.com/en-us/windows-server/administration/windows-commands/arp

https://docs.microsoft.com/en-us/windows-server/administration/windows-commands/ipconfig


C:\WINDOWS\system32>
C:\WINDOWS\system32>ipconfig  | findstr /I gateway
   Default Gateway . . . . . . . . . : 192.168.200.1

C:\WINDOWS\system32>ipconfig  | findstr /I mask
   Subnet Mask . . . . . . . . . . . : 255.255.255.0

C:\WINDOWS\system32>arp -a

Interface: 192.168.200.135 --- 0xf
  Internet Address      Physical Address      Type
  192.168.200.1         f0-9f-xx-xx-xx-xx     dynamic
  192.168.200.2         74-83-xx-xx-xx-xx     dynamic
  192.168.200.37        00-0c-xx-xx-xx-xx     dynamic
  192.168.200.100       bc-8c-xx-xx-xx-xx     dynamic
  192.168.200.205       c8-3a-xx-xx-xx-xx     dynamic
  192.168.200.209       c8-3a-xx-xx-xx-xx     dynamic
  192.168.200.245       00-0c-xx-xx-xx-xx     dynamic
  224.0.0.22            01-00-xx-xx-xx-xx     static
  228.67.43.91          01-00-xx-xx-xx-xx     static
  239.255.255.250       01-00-xx-xx-xx-xx     static

C:\WINDOWS\system32>arp -d *

C:\WINDOWS\system32>arp -a

Interface: 192.168.200.135 --- 0xf
  Internet Address      Physical Address      Type
  192.168.200.1         f0-9f-xx-xx-xx-xx     dynamic
  192.168.200.245       00-0c-xx-xx-xx-xx     dynamic
  224.0.0.22            01-00-xx-xx-xx-xx     static
  228.67.43.91          01-00-xx-xx-xx-xx     static

C:\WINDOWS\system32>
C:\WINDOWS\system32>ping 192.168.200.244

Pinging 192.168.200.244 with 32 bytes of data:
Control-C
^C
C:\WINDOWS\system32>arp -a

Interface: 192.168.200.135 --- 0xf
  Internet Address      Physical Address      Type
  192.168.200.1         f0-9f-xx-xx-xx-xx     dynamic
  192.168.200.37        00-0c-xx-xx-xx-xx     dynamic
  192.168.200.245       00-0c-xx-xx-xx-xx     dynamic
  224.0.0.22            01-00-xx-xx-xx-xx     static
  228.67.43.91          01-00-xx-xx-xx-xx     static

C:\WINDOWS\system32>ping 192.168.200.7

Pinging 192.168.200.7 with 32 bytes of data:
Reply from 192.168.200.7: bytes=32 time=3ms TTL=64

Ping statistics for 192.168.200.7:
    Packets: Sent = 1, Received = 1, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
    Minimum = 3ms, Maximum = 3ms, Average = 3ms
Control-C
^C
C:\WINDOWS\system32>arp -a

Interface: 192.168.200.135 --- 0xf
  Internet Address      Physical Address      Type
  192.168.200.1         f0-9f-xx-xx-xx-xx     dynamic
  192.168.200.7         b4-fb-xx-xx-xx-xx     dynamic
  192.168.200.37        00-0c-xx-xx-xx-xx     dynamic
  192.168.200.245       00-0c-xx-xx-xx-xx     dynamic
  224.0.0.22            01-00-xx-xx-xx-xx     static
  228.67.43.91          01-00-xx-xx-xx-xx     static

C:\WINDOWS\system32>
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No.2 Revision

updated 2021-06-07 16:38:16 +0000

grahamb gravatar image

arp -a is a passive action showing the contents of the local ARP cache.

You can use arp -d to remove individual entries or the whole cache with arp -d *
If there is no entry in the cache, then something needing to access a local (on same subnet) IP address (like ping) will force an ARP request.
In the example below there is only one interface. The subnet is determined from the Default Gateway and Subnet Mask.

arp -d will require Admin permissions.

https://docs.microsoft.com/en-us/windows-server/administration/windows-commands/arp

https://docs.microsoft.com/en-us/windows-server/administration/windows-commands/ipconfig

https://docs.microsoft.com/en-us/windows-server/administration/windows-commands/arp

https://docs.microsoft.com/en-us/windows-server/administration/windows-commands/ipconfig


C:\WINDOWS\system32>
C:\WINDOWS\system32>ipconfig  | findstr /I gateway
   Default Gateway . . . . . . . . . : 192.168.200.1

C:\WINDOWS\system32>ipconfig  | findstr /I mask
   Subnet Mask . . . . . . . . . . . : 255.255.255.0

C:\WINDOWS\system32>arp -a

Interface: 192.168.200.135 --- 0xf
  Internet Address      Physical Address      Type
  192.168.200.1         f0-9f-xx-xx-xx-xx     dynamic
  192.168.200.2         74-83-xx-xx-xx-xx     dynamic
  192.168.200.37        00-0c-xx-xx-xx-xx     dynamic
  192.168.200.100       bc-8c-xx-xx-xx-xx     dynamic
  192.168.200.205       c8-3a-xx-xx-xx-xx     dynamic
  192.168.200.209       c8-3a-xx-xx-xx-xx     dynamic
  192.168.200.245       00-0c-xx-xx-xx-xx     dynamic
  224.0.0.22            01-00-xx-xx-xx-xx     static
  228.67.43.91          01-00-xx-xx-xx-xx     static
  239.255.255.250       01-00-xx-xx-xx-xx     static

C:\WINDOWS\system32>arp -d *

C:\WINDOWS\system32>arp -a

Interface: 192.168.200.135 --- 0xf
  Internet Address      Physical Address      Type
  192.168.200.1         f0-9f-xx-xx-xx-xx     dynamic
  192.168.200.245       00-0c-xx-xx-xx-xx     dynamic
  224.0.0.22            01-00-xx-xx-xx-xx     static
  228.67.43.91          01-00-xx-xx-xx-xx     static

C:\WINDOWS\system32>
C:\WINDOWS\system32>ping 192.168.200.244

Pinging 192.168.200.244 with 32 bytes of data:
Control-C
^C
C:\WINDOWS\system32>arp -a

Interface: 192.168.200.135 --- 0xf
  Internet Address      Physical Address      Type
  192.168.200.1         f0-9f-xx-xx-xx-xx     dynamic
  192.168.200.37        00-0c-xx-xx-xx-xx     dynamic
  192.168.200.245       00-0c-xx-xx-xx-xx     dynamic
  224.0.0.22            01-00-xx-xx-xx-xx     static
  228.67.43.91          01-00-xx-xx-xx-xx     static

C:\WINDOWS\system32>ping 192.168.200.7

Pinging 192.168.200.7 with 32 bytes of data:
Reply from 192.168.200.7: bytes=32 time=3ms TTL=64

Ping statistics for 192.168.200.7:
    Packets: Sent = 1, Received = 1, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
    Minimum = 3ms, Maximum = 3ms, Average = 3ms
Control-C
^C
C:\WINDOWS\system32>arp -a

Interface: 192.168.200.135 --- 0xf
  Internet Address      Physical Address      Type
  192.168.200.1         f0-9f-xx-xx-xx-xx     dynamic
  192.168.200.7         b4-fb-xx-xx-xx-xx     dynamic
  192.168.200.37        00-0c-xx-xx-xx-xx     dynamic
  192.168.200.245       00-0c-xx-xx-xx-xx     dynamic
  224.0.0.22            01-00-xx-xx-xx-xx     static
  228.67.43.91          01-00-xx-xx-xx-xx     static

C:\WINDOWS\system32>