The Default Gateway is the IP Address of a router or a routing device to which all the packet to a destination for which the server doesn't have a route will be forwarded to. Most of the servers in any network leave the routing job to the routers meaning there will be a default gateway added to the system and very little (if any) static routes added to it. This makes management much easier.
This procedure should work on Redhat Enterprise Linux, Fedora, Centos.
DHCP, Dynamic Host Configuration Protocol is the protocol used by network devices like a PC or a printer (DHCP clients) to obtain IP Address, Default Gateway, Domain Name, DNS Servers, NetBIOS servers and more that helps the device to work properly in an IP Network.
While in an ideal scenario, most if not all organisations run the DHCP server on a Windows server or a Linux/Unix server. While this is justfiable in bigger corporate and enterprise networks, a smaller network like a branch office can be supported by a local Router, Switch or a Firewall can run a DHCP server without the need of an additional server hardware to run DHCP. Most of the routers, firewalls and some switches do have a DHCP server builtin. Most of the new Cisco Routers and Switches running Cisco IOS can run a DHCP server.
The Default Gateway or the Default Router is the IP address (IPv4) to which all the traffic to any target destination(s) which does not have a route in the Routing Table of the server will be forwarded.
This Default Gateway is maintained in the file
/etc/defaultrouter [IPv4 only]