Border Gateway Protocol Recommended Instructions

  • Import your network’s configuration files as described in BGP Data Extraction.

  • Analyse the BGP reports for integrity checks errors as described in BGP Reports.

  • View BGP options as described in BGP Options.

  • Open the BGP Map to view EBGP and IBGP peering relationships as described in BGP Map.

  • View routing table information and perform path analyses as described in BGP Routing Table and BGP Routes Analysis.

  • View BGP information associated with a node from the BGP Routes Analysis.

  • View, add, or modify BGP neighbor information as described in BGP Routing Table.

  • Apply, modify or add BGP policies as described in Apply, Modify, or Add BGP Polices.

  • Learn how the subnet file works as described in BGP Subnets , and work through an example where the AS_PATH attribute is used to influence routing.

  • Learn about getipconf’s bgp-related usage notes and bgp-related files as described Getipconf Usage Notes.

Definitions

Term

Definition

Autonomous Systems (AS)

A set of routers under a single technical administration, identified by its AS number (1 to 64,511 for registered Internet numbers and 64,512 to 65,534 for private AS numbers.)

EBGP

External BGP - BGP running between different ASs

IBGP

Internal BGP - BGP running within one AS

Peers or Neighbors

Two routers are called peers or neighbors if they exchange BGP information through an opened TCP (Transmission Control Protocol) connection.

Confederations

BGP confederations are used to reduce the number of IBGP connections needed in the full-mesh requirement. An AS’s routers are divided into multiple smaller private ASs, and the smaller private ASs come together to produce a public AS.

Route Reflectors

A route reflector is a BGP speaker that is specially configured and used to pass IBGP learned routes to a set of IBGP neighbors. This eases the fully meshed requirement of IBGPs and reduces the number of IBGPs peering within an AS.

Community

A community is a group of destinations that share common BGP attributes, filters, and policies. Routing decisions can be applied to the community (the group of routes).

Peer Groups

Instead of setting up a community (a group of routes), a peer group (a group of peer routers) can be established and configured with the same update policies, which simplifies configuration tasks and makes updating more efficient.

AS_PATH

BGP carries the AS numbers of the ASs that have been traversed, using the AS_PATH attribute in order to reject updates containing its own AS number to prevent loops.

LOCAL_PREF

When there is more than one path to a network destination outside of the current AS, each of the routers that link outside the AS can set a preference value (via the LOCAL_PREF attribute) for routes advertised into the AS. The LOCAL_PREF attribute is used to influence traffic leaving an AS.

MULTI_EXIT_DISC

The MULTI_EXIT_DISC (MED) is used between EBGP peers when there are multiple paths from one AS to another. It indicates to external neighbors which path is preferred into an AS. The MED attribute influences traffic entering an AS.

Weight

A Cisco-specific attribute in which higher-weight routes are preferred. Router-originated routes have a weight of 32768 by default and other routes have a weight of zero. Weight works similarly to LOCAL_PREF except that it only applies to routes within the box and is not communicated to other peers.

Cluster ID

A route reflector and its clients form a cluster. Usually a cluster has a single route reflector. For redundancy, a cluster may have more than one route reflector. When a cluster has more than one route reflector, all of the route reflectors in the cluster need to be configured with the same cluster ID.