Q. Why can’t I communicate with any computers outside my local subnet?

A. I recently had this exact problem. My connection had been working fine, then suddenly I couldn’t communicate with any computer outside my local subnet. Internet connectivity had also failed. These symptoms pointed to the gateway configuration, but I hadn’t changed anything. I could ping the gateway just fine. So, I ran the Ipconfig utility and saw the following output.

Windows IP Configuration

Ethernet adapter Local Area Connection:

Connection-specific DNS Suffix . :
IPv6 Address. . . . . . . . . . . . : 2002:4cb7:32c7:1234:c13b:de8e:5abc:330f
Temporary IPv6 Address. . . . . . : 2002:4cb7:32c7:1234:9c4d:fd1b:79c9:4318
Link-local IPv6 Address . . . . . : fe80::c13b:de8e:5abc:330f%8
IPv4 Address. . . . . . . . . . . : 192.168.1.15
Subnet Mask . . . . . . . . . . . : 255.255.255.0
Default Gateway . . . . . . . . . : fe80::21d:7eff:fe0d:1c91%8
                                    0.0.0.0
                                    192.168.1.1

Notice the second-to-last line: A 0.0.0.0 gateway (above the real gateway) was taking precedence, thus stopping traffic outside my subnet. I printed my routing table by entering

Usersjohn>route print

The output was

======================================================================

Interface List
8 ...00 1d 7d 07 a2 fc ...... Realtek RTL8168B/8111B Family PCI-E Gigabit Ethe rnet NIC (NDIS 6.0)
1 ........................... Software Loopback Interface 1
13 ...00 00 00 00 00 00 00 e0 Microsoft ISATAP Adapter
12 ...02 00 54 55 4e 01 ...... Teredo Tunneling Pseudo-Interface

=================================================================

IPv4 Route Table

=================================================================

Active Routes:
Network Destination Netmask Gateway Interface Metric
0.0.0.0 0.0.0.0 On-link 192.168.1.15 20
0.0.0.0 0.0.0.0 192.168.1.1 192.168.1.15 266
127.0.0.0 255.0.0.0 On-link 127.0.0.1 306
127.0.0.1 255.255.255.255 On-link 127.0.0.1 306
127.255.255.255 255.255.255.255 On-link 127.0.0.1 306
169.254.0.0 255.255.0.0 On-link 192.168.1.15 30
169.254.255.255 255.255.255.255 On-link 192.168.1.15 266
192.168.1.0 255.255.255.0 On-link 192.168.1.15 266
192.168.1.15 255.255.255.255 On-link 192.168.1.15 266
192.168.1.255 255.255.255.255 On-link 192.168.1.15 266
224.0.0.0 240.0.0.0 On-link 127.0.0.1 306
224.0.0.0 240.0.0.0 On-link 192.168.1.15 266
255.255.255.255 255.255.255.255 On-link 127.0.0.1 306
255.255.255.255 255.255.255.255 On-link 192.168.1.15 266

=================================================================

Persistent Routes:
Network Address Netmask Gateway Address Metric
0.0.0.0 0.0.0.0 192.168.1.1 Default

======================================================================

Nothing explained why I was seeing a 0.0.0.0 gateway,so I decided to try deleting the persistent route for my gateway.

Usersjohn>route delete 0.0.0.0 mask 0.0.0.0 OK!

Next, I checked Ipconfig. The 0.0.0.0 gateway along with my normal gateway of 192.168.1.1 had been removed. I went back into my adapter properties, set the default gateway, and the 192.168.1.1 gateway returned (without the 0.0.0.0). The problem was solved.

I'm not 100 percent sure why this problem occurred. After some research, I found that it might be an incompatibility between Windows Vista and my router.