Multiple IP Addresses on a Single NIC

Article translations Article translations
Article ID: 149399 - View products that this article applies to.
This article was previously published under Q149399
Expand all | Collapse all


A computer with two IP addresses assigned to its interface is unable to connect to computers across a router.


A single network interface card (NIC) configured with multiple IP addresses defined on different logical subnets will always use the first IP address defined in the TCP/IP configuration as its source address, regardless of the destination.


To resolve this problem, upgrade to Windows NT Workstation and Server version 4.0.

The problem does not occur if the computer has one NIC per IP address (two NICs).


Microsoft has confirmed this to be a problem in Windows NT versions 3.5 and 3.51. This problem was corrected in Windows NT Workstation or Server version 4.0.


Consider the following scenario:

A computer with a single NIC and two IP addresses--the first is, the second on the same segment where two routers are present, router 1 with IP address and router 2 with IP address

The route table is as follows:

Network Address  Netmask         Gateway Address  Interface   Metric   1   1   1   1   1   1   1   1   1
(Previous entry is an added static route)   1   1

Note that the interface is always Network is on the other side of router 2 ( and a static route was added for it. With this configuration, connectivity to any host on the local subnet with an IP address of 130.0.x.x or 130.1.x.x is possible. Connectivity to any host on the other side of router 1 ( is also possible. Connectivity to anything beyond router 2 is not possible. A network trace shows that the source IP address is when trying to reach a destination over router 2. Router 2 only knows about network and doesn't have a route defined for network

  • A static route can be added in router 2 to fix this problem (i.e. route add


Article ID: 149399 - Last Review: November 1, 2006 - Revision: 3.1
  • Microsoft Windows NT Workstation 3.5
  • Microsoft Windows NT Workstation 3.51
  • Microsoft Windows NT Server 3.5
  • Microsoft Windows NT Server 3.51

Give Feedback


Contact us for more help

Contact us for more help
Connect with Answer Desk for expert help.
Get more support from