A new feature has been added in the new 5.5 release of ESXi.  You can now clear the ARP cache on an ESXi server.  This is a very useful feature that should have always been part of ESXi.  This feature ONLY works with ESXi 5.5.  The KB article contents are below and were copied from http://kb.vmware.com/kb/2049667
Clearing the ARP cache table in ESXi 5.5Â (2049667)
Purpose
esxcli
 command introduced in vSphere 5.5 to clear the ARP table. ESXi 3.x, 4.x, and ESXi 5.0/5.1 do not include any mechanism to clear the ARP table.
For more information, see Troubleshooting network connection issues using Address Resolution Protocol (ARP) (1008184).
Resolution
esxcli network ip neighbor remove
 command to clear the ARP cache table.
To clear the ARP cache table in ESXi 5.5, use this command:
esxcli network ip neighbor remove [fusion_builder_container hundred_percent="yes" overflow="visible"][fusion_builder_row][fusion_builder_column type="1_1" background_position="left top" background_color="" border_size="" border_color="" border_style="solid" spacing="yes" background_image="" background_repeat="no-repeat" padding="" margin_top="0px" margin_bottom="0px" class="" id="" animation_type="" animation_speed="0.3" animation_direction="left" hide_on_mobile="no" center_content="no" min_height="none"][options]
Where options
 includes:
-i string
 orÂ--interface-name=string
WhereÂ
string
 is the name of the VMkernel network interface from which the neighbor entry must be removed. If this option is not specified, the neighbor is removed from all interfaces.-a address
 orÂ--neighbor-addr=address
WhereÂ
address
 is the IPv4/IPv6 address of the neighbor. This is mandatory.-N instance
 orÂ--netstack=instance
WhereÂ
instance
 is the network stack instance. If unspecified, the default netstack instance is used.-v number
 orÂ--version=number
WhereÂ
number
 is the IP version and can either be 4 or 6. This is mandatory.
For example, to delete the ARP entry for address 10.131.0.103
:
- Connect to the ESXi 5.5 host using SSH. For more information, see Using Tech Support Mode in ESXi 4.1 and ESXi 5.x (1017910).
- View the current ARP table using this command:
# esxcli network ip neighbor list
You see output similar to:
Neighbor     Mac Address     Vmknic   Expiry State Type
------------Â -----------------Â ------Â Â -------Â -----Â -----
10.131.0.103 00:1c:c4:a9:6f:fc  vmk0    908 sec       Unknown
10.131.0.179 00:1e:0b:bf:7a:50  vmk0   1062 sec       Unknown - To delete the ARP entry for addressÂ
10.131.0.103
, run one of these commands:# esxcli network ip neighbor -v 4 -a 10.131.0.103
# esxcli network ip neighbor --version=4 --neighbor-addr=10.131.0.103
- View the ARP table again using this command:
# esxcli network ip neighbor list
You see output similar to:
Neighbor     Mac Address     Vmknic   Expiry State Type
------------Â -----------------Â ------Â Â -------Â -----Â -----
10.131.0.179 00:1e:0b:bf:7a:50  vmk0   750 sec       Unknown
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