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

 

\ F.Q.D.N = Hostname    +  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

Learn more about Linux Interview Questions in this blog post. 

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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.

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