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Core Routing: Carrier Services

A Core Network's primary purpose in life is to provide a "service" of interconnectivity to someone or something. In a routing context, this means using MPLS in conjunction with BGP to "signal" customer services such as pseudowires, L2VPNs and L3VPNs across the network.

What are Core Routing Carrier Services?

Carrier Services are the primary function of a Core Routing network; they provide virtual private networks (VPNs) to each network "customer".  Typically this functionality is the primary reason for using Core Routing technologies such as MPLS (Multi-Protocol Label Switching) and BGP (Border Gateway Protocol).  Carrier Services utilize the core's  Underlay Transport to "signal" customer VPNs across the network.  Once established, these VPN services may be further enhanced using Traffic Engineering technologies.

Service Types

Customer VPNs can be provided in a few different ways:

  • as a simple point-to-point "pseudowire" that virtually connects a customer router at one site to another router belonging to the same customer at a different site, making the two routers appear to the customer as though they are directly connected to one another.
  • as a meshed L2VPN (Layer-2 VPN) that virtually connects customer routers at multiple distant sites, making all of the customer routers appear as though they are connected to each other on a shared layer-2 broadcast domain.
  • as a L3VPN (Layer-3 VPN) where the customer routers at each site directly exchange routing information with the core network, which in turn propagates that routing information across the network to the customer's routers at other sites.
Service Signaling

Because Carrier Services span across the network core, they must be signaled using certain technologies.  BGP is the most common protocol used to signal a service across a core network, but T-LDP (Targeted LDP) may also be used in certain circumstances.  Both BGP and T-LDP use MPLS labels to signal their services between edge routers.  The MPLS signaling labels for a given service are only relevant to the edge routers that connect to the service's customer; the routers in the network core as well as the edge routers not participating in the service are indifferent to the service's labels.

To learn more about any of these Underlay technologies, check out the following resources below or reach out to us at CoreNetworkingHelp@wwt.com