'/etc/sysconfig/network' file contains general information for all interfaces on your system. Like
However this file can be also used as a configuration file for eth0 [instead of ifcfg-eth0 when there is only one interface [NIC] on your system. For example you can remove the 'IPADDR' , 'NETMASK' & 'GATEWAY' entries from ifcfg-eth0 and add it to 'network' file
# cat /etc/sysconfig/network
After restarting the network, the above IP, netmask & gateway will be assigned to eth0.
But when you have more than one interface card, the individual interface card information's will be recorded in the file ifcfg-ethX in directory '/etc/sysconfig/network-scripts' instead. So if you have more than one NIC, then information for each NIC's will appear in separate files in the directory '/etc/sysconfig/network-scripts' with names of the form 'ifcfg-eth0' for eth0 'ifcfg-eth1' for eth1... etc