This article was previously published under Q149399
A computer with two IP addresses assigned to its interface is unable toconnect to computers across a router.
A single network interface card (NIC) configured with multiple IP addressesdefined on different logical subnets will always use the first IP addressdefined in the TCP/IP configuration as its source address, regardless ofthe destination.
To resolve this problem, upgrade to Windows NT Workstation and Serverversion 4.0.
The problem does not occur if the computer has one NIC per IP address (twoNICs).
Microsoft has confirmed this to be a problem in Windows NT versions 3.5 and3.51. This problem was corrected in Windows NT Workstation or Serverversion 4.0.
Consider the following scenario:
A computer with a single NIC and two IP addresses--the first is 22.214.171.124,the second 126.96.36.199--is on the same segment where two routers arepresent, router 1 with IP address 188.8.131.52 and router 2 with IP address184.108.40.206.
Note that the interface is always 220.127.116.11. Network 18.104.22.168 is on theother side of router 2 (22.214.171.124) and a static route was added for it.With this configuration, connectivity to any host on the local subnet withan IP address of 130.0.x.x or 130.1.x.x is possible. Connectivity to anyhost on the other side of router 1 (126.96.36.199) is also possible.Connectivity to anything beyond router 2 is not possible. A network traceshows that the source IP address is 188.8.131.52 when trying to reach adestination over router 2. Router 2 only knows about network 184.108.40.206 anddoesn't have a route defined for network 220.127.116.11.
A static route can be added in router 2 to fix this problem (i.e. route add 18.104.22.168 22.214.171.124).