Troubleshooting Your Network Connection

Below are some common problems our users have experienced trying to connect computers to the Caltech network, and their symptoms.

The ping program is very helpful in diagnosing network problems. Basically, it sends a little greeting which is network language for "hello, how's it going?" and then expects for a little confirmation back of "fine, thanks!". If you have never used ping before, IMSS staffers are happy to help you learn how to use it.

Problem: Server Problems at your Destination

Symptoms: Your computer can reach everything else except a particular server, which of course is the one you need to get to. For instance, if you're trying to get to http://www.google.com/ and cannot, but can get everywhere else on the web, the problem is very likely that Google is having problems at their end.

Solution: You can try sending in a trouble report to the administrators of the destination site, though they likely know already that there are problems. Your only other recourse is to take a deep breath and do something else until their server(s) come back online. If you know of a similar site or server to the one you cannot reach, you could also try that (for instance, using Yahoo rather than Google).

If you are having difficulty reaching a specific server at Caltech, but do not know how to contact the administrators of it, IMSS may be able to assist you in reaching them. Submit a request at http://help.caltech.edu (request type IMSS-->Other) briefly describing your situation and request the contact information for the administrators of the Caltech system you are trying to reach.

Problem: Bad Subnet Mask in Configuration

Symptoms: Cannot successfully ping computers on your same subnet (for example, your default router's IP address), but can successfully ping computers of your same subnet (for example, 131.215.48.254).

Solution: Doublecheck your computer's IP address configuration, according to the configuration guides by operating system link in the Campus Network Services section of this website, paying specific attention to the subnet mask in your configuration. That should correct the problem. If not, see below.

Problem: Bad Default Route

Symptoms: Can successfully ping computers on your same subnet (for example, your default router's IP address), but cannot successfully ping computers of your same subnet (for example, 131.215.48.254).

Solution: Doublecheck your computer's IP address configuration, according to the configuration guides by operating system link in the Campus Network Services section of this website. That should correct the problem. If not, see below.

Problem: Bad DNS Servers (Or None) in Configuration

Symptoms: Can successfully ping computers by IP address, but cannot ping computers by name (for example, its.caltech.edu).

Solutions: Doublecheck your computer's IP address configuration, according to the configuration guides by operating system link in the Campus Network Services section of this website, paying specific attention to the DNS servers listed in your configuration. That should correct the problem. If not, see below.

Problem: Bad IP Address in Configuration

Symptoms: Cannot ping anything successfully.

Solution: Doublecheck your computer's IP address configuration, according to the configuration guides by operating system link in the Campus Network Services section of this website, paying specific attention to the IP address assigned to your computer. That should correct the problem. If not, see below.

Problem: Network Access Blocked For Computing Security Reasons

Symptoms: Network access that used to work suddenly stops working. Can no longer access Caltech servers or off-campus systems. May or may not appear to have an IP address.

Solution: Check to see if your computer has been blocked from accessing the network, by entering your system's MAC address at the MAC Address Block Check webpage.

If your computer was indeed blocked, contact us at http://help.caltech.edu (request type IMSS-->Information Security-->Other). Consider registering as the contact for your computer by its MAC address at the MAC Registry webpage this way you will be contacted if there's a problem in the future.

Problem: Bad Hardware (Network Interface Card, Cabling, Wall Port, Wall Wiring, etc.)

Symptoms: Cannot ping anything successfully.

Solution: Doublecheck your computer's IP address configuration, according to the guides by operating system to be certain that a misconfiguration is not the cause of your problem. Submit a request at http://help.caltech.edu (request type IMSS-->Network, WIreless & Remote Access-->Other) with your exact location, your computer's operating system, your computer's MAC Address, whether you are using DHCP or a Static IP Address, the IP address you are using, and list what you have already doublechecked. We will arrange for a network engineer to test the connection to your wall port, and from there, narrow down if the problem is with our equipment, your cabling, or your network interface card.

If you are unable to send email, call the IMSS Help Desk at 626.395.3500 and ask the Help Desk representative to open a ticket with our Network group, being sure to provide all of the above details.

Other Problems:

If you have looked over this list and are still stumped, please submit a request at at http://help.caltech.edu (request type IMSS-->Network, WIreless & Remote Access-->Other) with your exact location, your computer's operating system, your computer's MAC Address, whether you are using DHCP or a Static IP Address, the IP address you are using, and list everything which you have already doublechecked in detail.

If you are unable to send email, call the IMSS Help Desk at 626.395.3500 and ask the Help Desk representative to open a ticket with our Network group, being sure to provide all of those details. We're happy to help get you back on the Caltech network.