An edge router (also called access router) is a network device located at the boundary of a network that connects to external networks, wide area networks (WANs) and the internet. Typically the edge router sends or receives data directly to or from other organizations' networks. The edge router is also the organization's network connection to the internet. 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:
- As external Border Gateway Protocol (BGP) routers that connect one autonomous system to other ASes, which includes connecting an enterprise network to the network edge of its internet service provider (ISP); and
- 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 will 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.