(1.2.3.4 is an arbitrary replacement but doesn't affect the basic issue) What is causing this? The systems in question have only one interface per subnet but both systems have multiple NICs which are on the same subnets. What I mean is this: on both systems NIC1 connects to subnet 1, NIC2 to subnet 2 and so on for five NICs and different subnets. The subnets do have different IP ranges (no overlap). 10.222.109.3 does happen to be on the same system as 1.2.3.4 but it doesn't have the same mac address and it is a physical interface. Address HWType HWAddress Flags Mask Iface 10.222.109.3 ether bc:30:5b:a6:c4:bf C eth9 . . . 1.2.3.4 ether bc:30:5b:a6:c4:bf C eth9 Leroy Tennison Network Information/Cyber Security Specialist E: leroy@xxxxxxxxxxxxxxxx 2220 Bush Dr McKinney, Texas 75070 www.datavoiceint.com TThis message has been sent on behalf of a company that is part of the Harris Operating Group of Constellation Software Inc. These companies are listed here . If you prefer not to be contacted by Harris Operating Group please notify us . This message is intended exclusively for the individual or entity to which it is addressed. This communication may contain information that is proprietary, privileged or confidential or otherwise legally exempt from disclosure. If you are not the named addressee, you are not authorized to read, print, retain, copy or disseminate this message or any part of it. If you have received this message in error, please notify the sender immediately by e-mail and delete all copies of the message.