Networking

• One of the key elements of connecting to different systems in the network configuration involved
• A Network is a set of hardware devices connected together, either physically or logically to allow them to exchange information.
• Network management is fairly easy when it comes to Ret Hat.
• Most of the network configuration is kept in files; therefore, adjusting these settings is simple.
• In the network system maintains the fully qualified domain name

  Let’s start by looking at the information about hostname & networking  

• To check the hostname: #hostname
• To Managing hostname temporarily:  --->#hostname     server254

• To Managing permanently: #vim /etc/sysconfig/network

NETWORKING          =YES HOSTNAME              = SERVER254 NETWORKING_IPV6=YES

• For avoiding graphical problems:

#vi /etc/hosts 192.168.0.254    Server254. Example.com    server254 :wq!

• To Manging IP – Address:
• To check the ipaddress:

Syn:  if config [options]   [interface] Options:         netmask Up Down Ex:  # if config  ethʘ

• To display all interfaces on the system

#ifconfig

• To change ip address temporarily:

Syn:     #if config ethʘ <ip-address> net mask <sub net mask> <up/down> #if config ethʘ 192.168.0.254 net mask       255.255.255.0 up #ifconfig ethʘ             To verify

• To change permanently:

(a)        #setup             (b)       System-config-network-tui --> you could also check the output of the interface config file #vim /etc/sysconfig/network-scripts/ifcfg- ethʘ Device             = ethʘ BOOTPROTO   =None ONBOOT         =Yes IPADDR            =192.168.0.254 NETMASK        = 255.255.255.0 :wq  

• To check the interface detected (or) not:

Syn:     # eth tool <interface> # eth tool eth ʘ

• To bring the signle interface down:

#ifdown eth ʘ

• To restore the interface that you just brought down:

#ifup eth ʘ *Note:

• Any time you make a change to an interface’s settings, you need to bring dwon that interface and then bring it back u again.

WARNING:  Restarting the network service interrupts all network connections and any client that is currently connected.

• Restart the network service as follows:

Syn: # service <service name> <stop/start/restart/status> # service network restart

• To check the all services status:

# service – status – all

• To Manage permanently:

Syn:     #chkconfig      --level <run levels>     <service name>          <on/off> #chkconfig      network on

• To check the status of the service:

# chkconfig –list network

• To disable the service at boot time:

#chkconfig network off     Routing:   When you have a system that has two or more network interfaces, they are called dual-bomed  (or) multi bomed systems. You need to make sure that each interface has a gateway that  it can route through. Syn:     route   [options, Add     Add a net route Del       Deletes an Existing route Flush   Flushes any temporary routes

• Let’s look at the current routes on the system:

# route

• To set default gateway:

#route add default gw 192.168.0.1 ethʘ

• To verify:

# route

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Networking utilities: Ping:  Tests the connectivity between two hosts #ping 192.168.0.254

• When you ping something on a linux host, unlike in windows, the ping continues until you cancel it. You can limit the number of ping requests sent by prefixing –c number – count in front of the destination host.

#ping –c 3 192.168.0.254 Net stat: Shows information about connections (open, closed and listening).

• Using net stat command to obtain information on routing tables, listening sockets, and established connections.

Syn: net stat [options] Options: -r         Displays the routing table. -I          Displays interface statistics -t         shows tcp connections -U        shows UDP connections -a         Displays all sockets (tcp, udp, or local) -p         Displays process Id’s -e         Displays Extended information.   --> To check that the connection is available for your clients: # netstat  - tuape  / grep ssh Client DNS Troubleshooting: /etc/sysconfig/network : contains the hostname of the system /etc/hosts  : contains the local IP to hostname mappings /etc/resolu.cong : contains the IP address of the DNS servers Nslookup : queries (or) looks up a domain name or system Ping     : Test connectivity between two hosts. Ethernet Bonding: Ethernet bonding is used to combine multiple interfaces into one, creating an increase in available bandwidth and redundancy. This is done by creating a special network interface file called as a channel bonding interface.