Linux Setting up your network

Basic Approaches Configure during installation –Disadvantage -> not able to redo easily –Advantage-> holds your hand Configure after installation –Disadvantage -> collision with other config tools –Advantage-> fairly easy to use (99.5% coverage) Access files directly –Disadvantage -> more details to know –Advantage-> access to everything and a deeper understanding

Access Files Directly Most of the files are in /etc Use installation to recognize NIC cards /etc/sysconfig to specify setup /etc/modules.conf to recognize cards /etc/rc.d/init.d to restart network after configuring Add manual routes to static-routes

/ etc Tons of configuration information Very small amount related to the configuration of the network Focus on /etc/sysconfig first Use the installation process to recognize the NIC cards. Edit sysconfig files afterwards if errors occur.

Recognizing cards Installation is reasonably sophisticated. Most cards will be recognized either with a generic driver or the real one. Use ifconfig to determine if card is recognized. (see next overhead) For older cards use /etc/modules.conf

ifconfig -> eth0 Link encap:Ethernet HWaddr 00:E0:7D:7A:AE:2C inet addr: Bcast: Mask: UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets: errors:0 dropped:0 overruns:0 frame:0 TX packets: errors:0 dropped:0 overruns:0 carrier:0 collisions:6947 txqueuelen:100 RX bytes: (12.3 Mb) TX bytes: (26.3 Mb) Interrupt:5 Base address:0xe000 lo Link encap:Local Loopback inet addr: Mask: UP LOOPBACK RUNNING MTU:16436 Metric:1 RX packets:1269 errors:0 dropped:0 overruns:0 frame:0 TX packets:1269 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes: (109.1 Kb) TX bytes: (109.1 Kb)

Cards Recognized.. Next? Check the configuration of the network Use netstat to check the routing tables Be sure the cards are connected to the right network if multiple cards (router) Use ping to check for connectivity.

netstat -nr -nr Kernel IP routing table Destination Gateway Genmask Flags MSS Window irtt Iface U eth U lo UG eth0

Problems? General Networking Examine the network configuration files / etc … sysconfig network [prompt]# cat network NETWORKING=yes FORWARD_IPV4=false HOSTNAME=testserver DOMAINNAME=localdomain GATEWAY= [prompt]#

Red Hat Fedora exception to network file Format is same but… FORWARD_IPV4 flag is overridden by an entry in a kernel configuration file named /etc/sysctl.conf net.ipv4.ip_forward = 1

Each Device / etc … sysconfig network network-scripts ifcfg-eth0 … [prompt]#cat ifcfg-eth0 DEVICE=eth0 BOOTPROTO=static IPADDR= NETMASK= NETWORK= BROADCAST= ONBOOT=yes [prompt]#

Recognizing a NIC /etc/modules.conf alias eth0 ne2k-pci alias eth1 3c5x9 options ne2k-pci irq=5 Forces the boot programs to examine additional “modules” for support in recognizing devices. Modules do other things and generally add functionality to the kernel. Odd format, but says to probe for a device using the ne2000 probe and name it eth0. Lets you control naming and also deal with two cards with identical type (not plug and play) Lets you add other info to help the probe software detect the device (specifying interrupt and i/o settings)

Other issues in recognizing Two cards of the same type are problematic if using older ISA cards –Most plug and play work fine –Is same and older May need to use separate software to set I/O And to set INTERRUPT Then use modules.conf to convey setting to boot. Look online for details for setting modules for specific network card types.

Restarting the network / etc … rc.d init.d network This is a script used during the boot process to start up the network. Don’t change it! Restart the network by 1.cd ing to the /etc/rc.d/init.d directory 2../network restart 3./sbin/service network restart

ping Don’t forget to use ping to test connectivity Use the lights to be sure interfaces are connected Use ifconfig to track the progress of communications through each interface “inch” your way out ( ping ing) if outside connection fails Be sure to configure forwarding on your router in the /etc/sysconfig/network file

static routes Used to add routes not obvious (most) Almost anything other than default gateway file is /etc/sysconfig/static-routes Example configuration line any net netmask gw See /etc/init.d/network script on next page –Shows file being read –Shows how the file adds static routes

/etc/init.d/network snapshot # Add non interface-specific static-routes. if [ -f /etc/sysconfig/static-routes ]; then grep "^any" /etc/sysconfig/static-routes | while read ignore args ; do /sbin/route add -$args done fi First line – names the file being read Second line – shows the file being filtered to look for lines beginning with “any” Third line – shows how to build the line on the file and how it as used with the route command