Cisco ASA, ESX/vSphere, and Duplicate IP’s

Summary:

Windows (2003/2008/R2) and/or Linux VM’s added to a VLAN and continuously report duplicate IP’s and Windows assign themselves APIPA (Private Address).

Symptoms:

1. (Windows) 169.254.x.x Address shows up as (Preferred) when running ipconfig /all in command prompt
2. Resetting Adapter pops up Duplicate IP Error.
3. Changing VM Network to a dummy network and vm nic reset, causes issue to go away.
4. Changing VM Network back to problem network clears issue until vm is reset or nic is reset.

Resolution:

Assuming the Cisco ASA is the cause, you can follow the below steps to rectify the issue:

1. Login to the Security Appliance ASDM
2. Select Device Setup
3. Expand Routing
4. Select Proxy ARP
5. Disable Proxy arp on the related interface (usually associated w/ your VLAN)
• Other command line method:
• sysopt noproxyarp <interface name>

If Windows is the issue for some reason, you can do this:

1. Start –> Run… –> Regedit
2. Find this key: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters
3. Insert a new DWORD value
4. Name the DWORD value “ArpRetryCount”
5. Change the value for the new entry to 0 if not already set that way.
6. Disable and Re-enable your network adapter to see if problem goes away.