Service Provider Core


The documents on this page pertain mostly to technologies like MPLS, iBGP, overlay technologies (like PBB-EVPN and VxLAN), Route Reflection and Confederations.

  • VPLS, PBB, EVPN and VxLAN Diagrams: These diagrams give an overview of the different overlay and L2VPN technologies currently used. Whilst not comprehensive, these diagram will help the understanding how they work and interrelate.

  •  Pseudowire Overview: Shows a conceptual overview of what an MPLS pseudowire (or xconnect) is, as well as how it is signalled.


  • VRF Route Leaking using Import and Export maps: This documents shows how traffic passes from one VRF to another and where all the config sits, using import and export maps.

  • SSO, GR, NSF and NSR: These terms are often  used for High Availability feature of devices in a Service Provider Core. This quick reference has been created in an attempt to clarify these often ambiguous or confusing features.

  • BGP Route Dampening: BGP Route Dampening is commonly used in Service Provider environments to protect the core network from BGP reconvergence events caused by unstable BGP routes. This document details how it works.
  • Route Reflection Rules: A quick reference guide to the principle and rules involved in route reflection.
  • 6to4 Tunnelling: A visual guide to 6to4 Automatic Tunnels, breaking down details like how IPv4 addresses are embedded in IPv6 addresses and how tunnels are formed.
  • Router Tables and Databases: This diagram, whilst not exhaustive, gives an overview of the tables and databases that you would encounter when looking at a router within a service provider network. It also provides the corresponding Cisco IOS commands.
  • Inter-AS MPLS Options: MPLS communications between Autonomous Systems can be achieved a number of ways and can sometimes be confusing to get your head around. This document outlines the different possibilities, giving diagrams of the overall concepts as well as CLI output from the downloadable labs that can be downloaded from here.
  • Carrier Supporting Carrier: When a Service Provider needs to connect two separate parts of its network together, sometimes it needs to call on another Service Provider to help. This document covers just such a scenario known as CsC or Carrier Supporting Carrier. An accompanying downloadable lab and full configs can be downloaded from here.
  • MPLS TE Database and RSVP Process: This document shows three basic concepts of MPLS Traffic Engineering: (1) How the Topology Database is populated, (2) How the RESV and PATH messages are used to signal an MPLS TE tunnel and (3) The contents of the RSVP messages.
  • MPLS DiffServ Tunnelling Models: Very quick reference document showing the Pipe, Short Pipe and Uniform Tunnelling Models.
  • Segment Types: This cheat sheet shows the major Segment Types involved in Segment Routing, describing the underlying idea of each, along with a diagram showing an example of how the forwarding is done.
  • Segment Routing – IGP Extensions: How TLVs are formatted and communicated as  IGPs extension can be confusing to keep track of. This document aims to provide a quick reference for how such extensions are applied to IS-IS and OSPF with regards to Segment Routing.
  • Segment Routing – Automated Steering: A quick reference overview of how Automated Steering works based on an example topology.
  • Segment Routing – On Demand Next Hop: Segment Routing ODN allows for dynamic instantiation of polices based on existing templates. This document describes how this is done with XR CLI configuration and output examples.
  • Segment Routing – Flexible Algorithm: Using Flex-Algos with Segment Routing you can create customised algorithms by defining optimisation metrics and constraints. Each Flex-Algo creates its own topology of the network right down its TI-LFA backup paths. This doc gives an introduction to Flex-Algo along with some basic IOS-XR configuration.
  • Segment Routing – Binding SIDs and the SRLG: Binding SIDs are a powerful tool within SR, that allows you to uniquely identify an SR Policy. It provides SID list simplification, opacity and protection from churn for outside domains. This document gives an overview of the basics.
  • IS-IS Neighborships: IS-IS is a common IGP used in Service Provider networks. This document shows how neighborships are formed and databases are synchronised for both Broadcast and Point-to-Point networks.
  • IS-IS MD5 Authentication: Example configuration for how to configure IS-IS MD5 Authentication for both IIH packets and for LSP, PSNP and CSNP packets.
  • LDP Basics: A brief overview of LDP Discovery, Neighborships and Modes.
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