Summary of troubleshooting a Network Fault

First, let's briefly introduce the company's network structure:

A vswitch is integrated, And the vro connects to the peer vro in Shanghai through the ddnleased line. The following clients are connected to the vswitch.

Server Overview:

The server system is a Win2000 Server and accesses the Internet through ISDN dial-up. The agent software is Wingate.

Fault description:

The ISDN device is normal, the connection is normal, but the Internet access is unavailable.

Troubleshooting:

The first thing that comes to mind is Ping this command to test the connection.

I entered: Ping www.163.com

Returned information:
Pinging 163.com [202.106.185.77] with 32 bytes of data:
Reply from 172.16.64.1: Destination Unreachable
Reply from 172.16.64.1: Destination Unreachable
Reply from 172.16.64.1: Destination Unreachable
Reply from 172.16.64.1: Destination Unreachable

According to the returned message, it seems a bit incorrect. Why do I ping 163.comand return 172.16.64.1.
This is the IP address of the Shanghai router. However, in the first sentence, the IP address of 163.com is 202.106.185.77. This
It indicates that DNS is correct! The problem may be routing.

Another idea:
Try to unplug the network cable connected to the network card. Check whether the ISDN connection is normal without passing through the route.
Test result: everything is normal. Using ipconfig, you can clearly see the IP address automatically allocated locally.

Problem determination:
This indicates that the data can be normally sent out without routing. However, after the network cable is plugged in, the fault persists.
After contacting the Shanghai Information Department, The vro of the other party has closed port 80 to prevent Internet access.
So I tried to access the Internet using the proxy method and set the proxy server connected to the ISDN in the IE attribute,
Still not. It seems that data packets still cannot be used out. It is estimated that the other party's deny has dropped most of the proxy ports.

After thinking about it, I suddenly thought that Win2000 also had a NAT Function, so I checked the route table.
Enter the route print command in DOS
The routing table shows that all the default routes are routed through the address 172.16.64.1.
That is, the 0.0.0.0 address is forwarded to 172.16.64.1.
I think, if I do not forward it to this vro, will the problem be solved?
Try to delete the default route and run the route Delete 0.0.0.0 command.
Disconnect the ISDN connection again and restart the ISDN connection.
Ping 163.com, successful. (Note: The network cable is not switched out this time)
The fault is successfully rectified.

Written by willpower, 2003.7.14