What is a Core Routing Underlay?
As the foundational layer of any Core Routing network, the Underlay Transport is what provides basic reachability between network segments. This reachability, which is the network's own awareness of how to get around itself, is the foundation for the Carrier Services and Traffic Engineering capabilities that the network provides as a service to its customers.
Interior Routing Protocols
The most basic element of an Underlay is its interior routing protocol, which in a Core Routing network is either IS-IS (Intermediate System to Intermediate System) or OSPF (Open Shortest Path First). Regardless of which protocol is used, the functional purpose is the same:
- to form neighborships between directly-connected routers
- to share network reachability information between those neighbors
- to calculate the best paths to reach any given network segment from every router
Interior Transport Mechanisms
In addition to the routing protocol that teaches each router how to reach distant network segments, there is a critical transport mechanism known as MPLS (Multi-Protocol Label Switching). MPLS allows Core Routing networks to efficiently shuttle packets across the network by associating a very small "label" with each IPv4 or IPv6 network segment and then using the label to "fast switch" rather than process the much-longer IP headers. The association between an MPLS label and an IP network segment is known as a "binding", and is typically established using a protocol called LDP (Label Distribution Protocol) or with Segment Routing.
To learn more about any of these Underlay technologies, check out the following resources below or reach out to us at CoreNetworkingHelp@wwt.com
