Networking in linux

To start network services:
# /etc/rc.d/init.d/network start

To stop network services:
# /etc/rc.d/init.d/network stop

To restart network services:
# /etc/rc.d/init.d/network restart

To view the network configuraiton:
# ifconfig [or]
# ip addr show

To configure an interface :
# ifconfig eth0 192.168.0.1 netmask 255.255.255.0 up
# Modify the file /etc/sysconfig/network-scripts/ifcfg-eth0

To configure alias on eth0 :
# ifconfig eth0:1 192.168.0.2 netmask 255.255.255.0 up

To list routing table :
# route

To add the default gateway to the routing table:
# route add default gw 192.168.0.15
[or]
# ip route add default via 192.168.0.5

To add a route for a specific host:
# route add -host 11.0.0.2 gw 192.168.0.115

To add a route for a specific network:
# route add -net 11.0.0.0 gw 192.168.0.115

Daemon used for dynamin routing/ Uses RIP: routed

Command to start routed daemon:
# rcrouted start

Configure a network card:
# ip link set mtu 9000 dev eth0

To show the network links:
# ip link show

To view ARP cache:
# arp -n

To remove an ARP entry:
# arp -d 192.168.1.1

To modifiy the host name resolution order, Modify the below file:
# cat /etc/host.conf
order hosts,bind

To modify the DNS server info:
# cat /etc/resolv.conf
search openna.com
nameserver 218.104.16.6
nameserver 218.104.16.12

To configure networking in Linux, modify the below file:
# cat /etc/sysconfig/network
NETWORKING=yes
NETWORKING_IPV6=yes
HOSTNAME=myserver
GATEWAY=192.168.1.1
GATEWAYDEV=eth0

To enable IP Forwarding:

For RHEL 6.2,
a. Add the below lines to /etc/sysctl.conf file
# Enable packet forwarding
net.ipv4.ip_forward = 1

b. Restart network services
# /etc/rc.d/init.d/network restart

For RHEL version lesser than 6.2,
a. Modify /etc/sysconfig/network
b. Restart network services