core router & edge router

core router

A core router is a router that forwards packets to computer hosts within a network (but not between networks). A core router is sometimes contrasted with an edge router, which routes packets between a self-contained network and other outside networks along a network backbone.

edge router

An edge router is a specialized router located at a network boundary that enables a campus network to connect to external networks. They are primarily used at two demarcation points: the wide area network (WAN) and the internet. Typically, the edge router sends or receives data directly to or from other organizations' networks, using either static or dynamic routing capabilities. Handoffs between the campus network and the internet or WAN edge primarily use Ethernet, usually Gigabit Ethernet copper or Gigabit Ethernet over single or multimode fiber optics. In some instances, an organization maintains multiple isolated networks of its own and uses edge routers to link them together instead of using a core router.

Edge routers are often hardware devices, but their functions can also be performed by software running on a standard x86 server. At its most essential level, the internet can be viewed as the sum of all the interconnections of edge routers across all participating organizations, from its periphery -- small business and home broadband routers, for example -- all the way to its core, where major telecom provider networks connect to each other via massive edge routers.

Types of edge routers and how they work

Edge routers are divided into two different types: subscriber edge routers and label edge routers.

Subscriber edge routers function in two ways:

1. As external Border Gateway Protocol (BGP) routers that connect one autonomous system (AS) to other ASes, which includes connecting an enterprise network to the network edge of its internet service provider (ISP); and

2. As small or midsize business (SMB) or consumer broadband routers connecting a home network or small office to an ISP's network edge.

Label edge routers, which are used at the edge of Multiprotocol Label Switching (MPLS) networks, act as gateways between a local network and a WAN or the internet and assign labels to outbound data transmissions. Edge routers are not internal routers that partition a given AS network into separate subnets. To connect to external networks, routers use the internet protocol (IP) and the Open Shortest Path First (OSPF) protocol to route packets efficiently.

Edge routers play a fundamental role as more services and applications begin to be managed on an organization's network edge rather than in its data center or in the cloud. Services considered suitable for edge router management include wireless capabilities often built into network edge devices, Dynamic Host Configuration Protocol (DHCP) services and domain name system (DNS) services, among others.

Difference between edge routers and core routers

In general, edge routers accept inbound customer traffic into the network. These edge devices characterize and secure IP traffic from other edge routers, as well as core routers. They provide security for the core. By comparison, core routers offer packet forwarding between other core and edge routers and manage traffic to prevent congestion and packet loss. To improve efficiency, core routers often employ multiplexing.

Security considerations

Because edge routers serve as a connection point between external networks, security is an issue, since enterprises can't control who might try to access the corporate network.