Basic Network Config

The following files may be touched by configuring a computer name, IP, network, or domain.
This is for a fixed IP:

/etc/hosts
/etc/sysconfig/network
/etc/sysconfig/network-scripts/ifcfg-eth0
/etc/resolv.conf

DHCP setup:

/etc/sysconfig/network
/etc/sysconfig/network-scripts/ifcfg-eth0

The RedHat setup command

use the arrow keys to scroll down to Network configuration
configure IP address, Netmask, Default gateway, and Primary nameserver
You can also configure your machine to be a DHCP client with setup

Look in /etc to see which files were modified by setup using ls -lt to sort by time stamp.

% ls -lt | head

You will also find that /etc/sysconfig/network and /etc/sysconfig/network-scripts/ifcfg-eth0 were modified.

To bring up the network, specifying IP, netmask, and broadcast using the ifconfig command:

# ifconfig eth0 10.2.135.201 netmask 255.255.255.0 broadcast 10.1.255.255 up

Then you will need to set the default router:

# route add default gw 10.2.135.1

The netstat command

Check the kernel routing tables:

# netstat -nr
Kernel IP routing table
Destination   Gateway       Genmask        Flags MSS Window irtt Iface
192.168.1.0   0.0.0.0       255.255.255.0 U       40 0         0 eth0
127.0.0.0     0.0.0.0       255.0.0.0      U       40 0         0 lo
0.0.0.0       192.168.1.1   0.0.0.0        UG      40 0         0 eth0

Netstat Flags

U: the interface is up
G: the route is to a gateway

Check interface statistics:

$ netstat -i
Kernel Interface table
Iface   MTU Met   RX-OK RX-ERR RX-DRP RX-OVR   TX-OK TX-ERR TX-DRP TX-OVR Flg
eth0   1500   0 944869      0      0      0 1399218      0      0      0 BMRU
lo    16436   0   25770      0      0      0   25770      0      0      0 LRU

MTU
RX: packets received
TX: packets transmitted
OK: error-free
ERR: damaged
DRP: dropped
OVR: lost because of over-run

Display sockets waiting for connections on your machine, also established connections.

# netstat -ta
Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address           Foreign Address     State
tcp        0      0 *:32768                 *:*                 LISTEN
tcp        0      0 *:sunrpc                *:*                 LISTEN
tcp        0      0 *:x11                   *:*                 LISTEN
tcp        0      0 ns:domain               *:*                 LISTEN
tcp        0      0 oaxaca:domain           *:*                 LISTEN
tcp        0      0 *:ssh                   *:*                 LISTEN
tcp        0      0 oaxaca:rndc             *:*                 LISTEN
tcp        0      0 oaxaca:x11-ssh-offset   *:*                 LISTEN
tcp        0      0 oaxaca:ssh              ponto:34429         ESTABLISHED

Connectivity tests:

Try to ping yourself, then your default router, then your Name Server

# ping 10.2.135.201
# ping 10.2.135.1
# ping 172.20.2.15
How does your system restart the network services?
How do these services start at boot time? Which run-levels support networking?

# service network restart
or
# /etc/init.d/network restart

Is DNS Resolving hostnames?

# nslookup google.com
Non-authoritative answer:
Name: google.com
Address: 216.239.35.100
Name: google.com
Address: 216.239.51.100

Check your nameserver config file:

# cat /etc/resolv.conf
search miracosta.edu
nameserver 172.20.2.15
nameserver 172.20.2.10

Loading kernel modules

Very few drivers are built into the Linux kernel.
They provided as dymanically loadable modules.
This keeps the kernel small and ensures you only load what you need.

Network Card Drivers Location

/lib/modules/`uname -r`/kernel/drivers/net

modprobe is the preferred way to load a module

it will load any additional modules on which your module may depend. (man depmod)
It doesn't require you type the full path to the module

# modprobe tlan

insmod requires the full path to the module for loading modules

You must insmod all dependencies by hand

# insmod /<full-path-to-module>/tlan.o

Options can be used with the insmod command, here we support the I/O port address

# insmod ne.o io=0x300

depmod computes module dependencies

updates file: /lib/modules/`uname -r`/modules.dep

# depmod -a

lsmod to list loaded kernel modules

# lsmod

rmmod to remove (unload) kernel modules

# rmmod <module-name>

The /etc/modules.conf file

configuration file for loading kernel modules
the file is optional and can be used to change the behavior of modprobe and depmod

$ cat /etc/modules.conf
alias parport_lowlevel parport_pc
alias eth0 3c59x
alias scsi_hostadapter sym53c8xx
alias eth1 tlan
alias usb-controller usb-ohci
alias char-major-188 visor
alias sound-slot-0 sb
post-install sound-slot-0 /bin/aumix-minimal -f /etc/.aumixrc -L >/dev/null 2>&1 || :
pre-remove sound-slot-0 /bin/aumix-minimal -f /etc/.aumixrc -S >/dev/null 2>&1 || :

Some modules require specifying options such as IRQ and I/O port address (excerpt from modules.conf):

alias eth0 3c503
optoins 3c503 irq=5 io=0x300