The terms and concepts presented in this appendix should prove helpful in understanding the BGP domain discovered and monitored by Network Protocol Manager for BGP.

Begin by examining Interior gateway protocol and exterior gateway protocol links.

Figure 1. Interior gateway protocol and exterior gateway protocol links

The links between the routers within an independent network, or autonomous system (AS), are referred to as Interior Gateway Protocol (IGP) links. The links between routers in different autonomous systems are referred to as Exterior Gateway Protocol (EGP) links. BGP is an EGP.

  • AS

    Autonomous system. A collection of networks, or more precisely, the routers joining those networks, that are under the same administrative authority and that share a common routing strategy.

  • BGP

    Border Gateway Protocol. A routing protocol, which is defined in RFC 1657, that updates routes between autonomous systems.

  • BGP neighbors

    BGP speakers that communicate with one another. External BGP neighbors (also known as external BGP peers) are in different autonomous systems, while internal BGP neighbors (also known as internal BGP peers) are in the same autonomous system. Normally, external neighbors are adjacent to each other and share a subnet, while internal neighbors may be anywhere in the same autonomous system.

  • BGP network

    Interconnected routers that are running BGP services.

  • BGP peers

    See BGP neighborsin this list.

  • BGP router

    A router that is running a BGP service.

  • BGP service

    A BGP process: An instance of the BGP routing protocol that is running in memory.

  • BGP session

    A link between BGP speakers. Sessions between BGP speakers of different autonomous systems are referred to as external sessions or external links. Sessions between BGP speakers within the same autonomous system are referred to as internal sessions or internal links.

  • BGP speaker

    Any BGP router that forms a BGP session with any other BGP router.

  • Confederation

    A mechanism used to scale BGP implementations by reducing the number of IBGP peering sessions. Essentially, the parent autonomous system is split into multiple sub autonomous systems, referred to as BGP confederation members . To the outside world, the confederation looks like a single autonomous system.

  • EBGP

    External BGP. A session between two BGP peers in different autonomous systems, for the purpose of communicating external routing information between the autonomous systems.

  • EGP

    Exterior Gateway Protocol. A routing protocol used to exchange routing information among two routers in a network of autonomous systems. An EGP protocol maintains routes between autonomous systems.

  • IBGP

    Internal BGP. A session between two BGP peers in the same autonomous system, for the purpose of communicating externally derived routing information within the autonomous system. IBGP peers can be attached by using a full mesh topology or the Route Reflector (RR) model.

  • IGP

    Interior Gateway Protocol. A routing protocol, such as Open Shortest Path First (OSPF), used to calculate routes and exchange routing information among routers within an autonomous system.

  • MTU

    Maximum transmission unit. A setting that controls the maximum IP packet size that a PC will send.

  • Multi-access segment

    A network segment supporting three or more routers. A network segment is part of an Ethernet or other network on which all message traffic is common to all nodes, that is, a message is broadcast from one node on the segment and received by all others on the segment.

  • Route reflector

    An alternative to the IBGP full mesh topology. In this model, an IBGP peer that is configured as a route reflector is responsible for passing IBGP learned routes to a set of IBGP neighbors. The route reflector model may be implemented for an entire autonomous system or within individual BGP confederation members.

  • Route reflector cluster

    Two or more route reflectors that back up the same set of IBGP peers and share the same cluster ID.

  • VLAN

    Virtual Local Area Network. A network of computers that behave as if they are connected to the same wire even though they may actually be physically located on different network segments of a LAN. VLANs are configured through software rather than hardware, which makes them extremely flexible.

  • VPN

    Virtual Private Network. A private-access network over public connections.