Network Configuration in Linux : PART 2

In This part 2 we are going to see the below points ,


5.Configuring IP address for interface?
6.How to define the routing ?
7.How to activate / deactivate network interfaces ?
8.How to enable IP Forward in Linux?
9.Speed and Duplex setting for interface?
10.Usefull commands in Linux for network troubleshoot.

  5. Configuring IP address for interface:

A.Command Line using ifconfig   //Temperary

  # ifconfig eth0   XXX.XXX.XXX.XXX netmask 255.255.255.0 broadcast XXX.XXX.XXX.255
B.Manually assign IP in config file - /etc/sysconfig/network-scripts/ifcfg-ethX  /permanent

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

For Alias IP

  #vi /etc/sysconfig/network-scripts/ifcfg-eth0:0

C.Using GUI Tool - /usr/sbin/system-config-network


6. How to define / add routing ?


A. Through 'route' command

   route add default gw XXX.XXX.XXX.XXX dev eth0
   route add  -net  XXX.XXX.XXX.0  netmask 255.255.255.0 gw XXX.XXX.XXX.XXX dev eth0

B. Modify  the config file -  /etc/sysconfig/static-routes   //only for static routes

C. Define the parameter in  config file - /etc/sysconfig/network-scripts/ifcfg-ethX




7. Activate deactivate Network interfaces:


A. Activate:

   # /sbin/ifup eth0  (or) #ifconfig eth0 up
B. De-Activate:

   # /sbin/ifdown eth0 (or) #ifconfig eth0 down
   

8 .Enable IP forward:

A. Turn on IP forwarding to allow Linux computer to act as a gateway or router.

#echo 1 > /proc/sys/net/ipv4/ip_forward

B. Modify the config file entry - /etc/sysctl.conf

  #vi /etc/sysctl.conf

  net.ipv4.ip_forward = 1


C. Verify ip forward

#cat /proc/sys/net/ipv4/ip_forward

1



9. Speed and Duplex setting in  Linux ?

A. Using the command : mii-tool  // view, manipulate media-independent interface status

 To view the speed - # mii-tool -v

 To set the speed  - #mii-tool -F option
                             #mii-tool -A option

B.Using the command : ethtool    // Display or change ethernet card settings

ethtool -g eth0     Queries ethernet device for rx/tx ring parameter information.
ethtool -a eth0     Queries ethernet device for pause parameter information.
ethtool -c eth0     Queries ethernet device for coalescing information.
ethtool -i eth0     Queries ethernet device for associated driver information.
ethtool -d eth0     Prints a register dump for the specified ethernet device.
ethtool -k eth0     Queries ethernet device for offload information.
ethtool -S eth0     Queries ethernet device for NIC and driver statistics.


10. Usefull commands and files in Linux for netowrk troubleshoot:

1. /etc/rc.d/init.d/network   start - command to start, restart or stop the network

2. /etc/inetd.conf  -  Network Socket Listener Daemons

   - The network listening daemons listen and respond to all network socket connections made on the TCP/IP ports assigned to it. The ports are defined by the file /etc/services
  
   - Entries in this file consist of a single line made up of the following fields:

        service socket-type protocol wait user server cmdline

Note : The inetd daemon must be restarted to pick up the changes made to the file:
       
        #/etc/rc.d/init.d/inetd restart

3.netstat - Display connections, routing tables, stats etc

    List all connected processes: #netstat -nap
    Show network statistics:      #netstat -s
    Display routing table info:   #netstat -rn
    Display interface statistics: #netstat -i

4.traceroute - print the route packets take to network host

5. socklist - Display list of open sockets, type, port, process id and the name of the process. Kill with fuser or kill

6. nslookup - Give a host name and the command will return IP address. Note that nslookup does not use the /etc/hosts file

7. Mii-tool - view, manipulate media-independent interface status

8. ethtool - Display or change ethernet card settings

9. tcpdump - Dump traffic on a network.