Linux / Unix Network Troubleshooting Guide

To use a Linux or Unix computer with ResNet, it needs to have an Ethernet adapter installed and a DHCP client installed and enabled. This document does not try to explain network card driver installation due to the complexity. It is assumed the user has a basic understanding of the OS, has already installed the network card, and has the necessary kernel modules loaded in or compiled. For detailed instructions on installing network card drivers or kernel modules, as well as configuring the network adapter card to use DHCP, we suggest reading the various applicable HOW-TO documents that can be found at sites such as:

The Linux Documentation Project

Free BSD

Driver / Module

Linux

Under Linux the drivers for a network card are called modules and must be loaded into the kernel. Most Linux distributions come with a large number of modules compiled and ready to be inserted into the kernel. Before randomly inserting modules, check that the module is not already loaded, and that it is the correct module for the network card you are using. The lsmod command show currently loaded modules. Common modules are the tulip module, used by PCI Netgear network cards, and the eepro module used by Intel EtherExpress PCI cards. There are many more modules. If Linuxconf is available on the computer, a list of modules is supplied in a drop down menu under the Host Name and IP devices section. If the network adapter is ISA, it will also need it's IRQ and IO ranges specified, which may be done in Linuxconf or in the /etc/modules.conf file. To load a module for a PCI network adapter, the simplest way is to use the modprobe command, followed by the named of the kernel module, such as modprobe tulip. The kernel modules are kept in the /lib/modules/kernel_name directory where kernel_name is the name of the kernel being used, i.e.: Linux or linux-2.4.17.

Unix

Most variances of Unix support some method of loading modules into the kernel. FreeBSD for example uses the commands kldload, kldunload, and kldstat to manage the loaded kernel modules. Solaris may use the commands modload, modunload, and modinfo. Please refer to documentation for your specific Unix on loading and unloading kernel modules.

Connectivity

If you are having trouble connecting to the ResNet, one of the first items to check is whether or not the computer has received an IP address. The ifconfig utility is used for this. Type ifconfig -a to list all configured network adapters. It will list IP addresses for each adapter. If the network adapter does not have an IP address which starts 10.0. restart the dhcp client on the computer. Each OS and distribution may use a different dhcp client program; common dhcp client programs are dhcpcd, pumpd, and dhcleint. After restarting the dhcp client, recheck the IP address of the adapter using ifconfig -a. If the network adapter still does not have a correct IP address, refer to the Linux network setup guides to enable it to use DHCP.

Routes

If the computer has not yet been registered but has received an IP address that begins with 192.168.1 and it does not bring up the ResNet registration web page when opening a web browser, first check the DNS configuration file as described under the DNS section below. If that information is correct, it will be necessary to check the default routes. Type netstat -r to display routes that are enabled on the computer. Prior to registering on the ResNet, the default route should be shown as 192.168.1.1 .If it is not listed in the list, it will either need to be added manually using route add default gw 192.168.1.1 , or more appropriately, refer to the Linux network setup guide to enable DHCP which will automatically set it up for you. If the computer has been registered and has received an IP address that begins with 155.31 but you cannot get to web pages when opening a web browser, first check the DNS configuration file as described under the DNS section below. If that information is correct, it will be necessary to check the default routes. Type netstat -r to display routes that are enabled on the computer. Once registered on the ResNet, the default route should be shown as 155.31.*.* .If it is not listed in the list, refer to the Linux network setup guide to enable DHCP which will automatically setup the default route for you. It is possible to add the route manually using route add default gw 155.31.*.*, but this is very difficult and requires you know the default gateway for your subnet. You can find the default gateway from a roommate's computer if it has already been registered, but if the network is changed, your computer won't be updated. Thus we still strongly recommend the computer be setup to use DHCP to receive all it's IP, DNS, and routing information via DHCP.

If the computer has a correct IP address, and all the routing information appears, you can test it's network connectivity by pinging the default gateway. Find the default gateway by typing netstat -r. Then ping it by typing ping IP_ADDRESS, where IP_ADDRESS is the IP address of the gateway gotten from the netstat -r command. Use the key combination CTRL-C to stop pinging the gateway. You should receive output from it showing the time it takes a packet to be sent and return in the form of:

PING 10.0.0.254 (10.0.0.254): 56 data bytes 64 bytes from 10.0.0.254: icmp_seq=0 ttl=255 time=0.689 ms --- 10.0.0.254 ping statistics --- 1 packets transmitted, 1 packets received, 0% packet loss round-trip min/avg/max/stddev = 0.689/0.689/0.689/0.000 ms round-trip min/avg/max/stddev = 0.689/0.689/0.689/0.000 ms

DNS

The DHCP process assigns DNS information when your computer requests an IP address. Typically, there are no extra steps necessary to setup your computer to receive and use DNS server information. DNS can be a problem under some Unix distributions however, and if you can ping hosts or access a website by typing in it's IP address but not host name, the following information might help. The /etc/resolv.conf file should contain entries for the domain in which the machine exists and the nameserver assigned by the DHCP client. Various Unix and Linux DHCP client don't assign the DNS information to this file.

To test DNS connectivity, the command nslookup, and more recently the commands dig and host, are used. Typing host mhc.edu should return an IP address of the computer mhc.edu. Typing dig will list the root DNS server you are using. If neither of these commands are available, typing nslookup will start the program, from which typing mhc.edu will return the default nameserver as well as the IP address of the computer mhc.edu. Exit the nslookup program by typing exit.