Article ID: 113342 - Last Review: February 20, 2007 - Revision: 2.3

How to Test a TCP/IP Router or Multihomed Host

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This article was previously published under Q113342

SUMMARY

If you are on a subnet and are having problems talking to another subnet through TCP/IP, the following information can help you determine if the problem is with the router.

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MORE INFORMATION

To troubleshoot router problems, you need a network map and the Internet addresses and subnet masks for your node, the router, the remote side of the router, and the destination node.

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Example

                          Two Subnets One Router
                          ----------------------
                              |   ROUTER   |
                          ----------------------
              195.22.3.1  >   |            |   < 195.22.4.25
              255.255.255.0   |            |   255.255.255.0
                              |            |

  |---------------------------|            |---------------------------|

                  |                                   |
                 YOU                              DESTINATION
             195.22.3.33                          195.22.4.66
            255.255.255.0                        255.255.255.0

Use the PING command to access your computer. For example:
ping 195.22.3.33

If this PING works, your node is probably okay.
Use the PING command to access the 'near' side of the router. For example:
ping 195.22.3.1

If this PING works, this side of the router is okay.

NOTE: Because you can ping this address does not necessarily mean this is a router.
Use the PING command to access the 'far' side of the router. For example:
ping 195.22.4.25

If this PING works, the router is working.

If it does not work, have someone use the PING command
ping 195.22.4.25

from the destination node (195.22.4.66).

If this PING works, the router is bad.
Use the PING command to access the remote host. For example:
ping 195.22.4.66

If this works, TCP/IP should be working fine.

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Notes

In most cases, the subnet mask should be the same for all nodes on the same side of the router.
The router in this case could be a multihomed Windows computer or server (a Windows computer or server with two or more network cards installed).
There could be two routers in separate sites performing the same job as above; if this is the case, treat this situation the same as above. (Keep in mind that each router could have a near and far side depending on the configuration.)
It is suggested to not use the node name when you are testing the router; use the Internet address. This will avoid any problems with the hosts file or domain name server.

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