6.1 VLAN Issues
6.1.4 Finding the route between VLANs
The Route Processor contains most of the system memory components and the main system processor. 

A default gateway is simply a router interface, normally referenced with an IP address. 

A default router is a router with at least one interface serving as a default gateway. For DHCP, a default router is a router that is providing a pool of IP addresses. 

Connecting the separate subnets through a Route Processor introduces the issue of how end-user devices can communicate with other devices through multiple LAN segments. Some network devices use routing tables to identify where to deliver packets outside of the local network segment. Even though it is not the responsibility of end-user devices to route data, these devices still must be able to send data to addresses on subnets other than their own.

So that each end device does not have to manage its own routing tables, most devices are configured with the IP address of a designated Route Processor. This designated Route Processor is the default router to which all nonlocal network packets are sent. The Route Processor then forwards the packets toward the appropriate destination. A network device's default router IP address depends on which IP subnet contains that network device.