BGP overview

Introduction

BGP is an inter-AS routing protocol. BGP allows devices to exchange network reachability information. The two types of BGP are:

• IBGP—to communicate with peer devices in the same AS. Routes received from a device in the same AS are not advertised to other devices in the same AS but can be advertised to an EBGP peer.

• EBGP—to communicate with peers in different ASs. Routes received from a device in another AS can be advertised to EBGP and IBGP peers.

See “BGP” in the NSP NFM-P Classic Management User Guide for information about how to configure BGP using the NFM-P. See the appropriate device documentation for information about router-specific BGP configurations.

BGP and CPAM

The CPAM extracts BGP route information from the BGP RIB that is maintained by a CPAA.

Network and element management systems, such as the NFM-P, can be used to configure BGP on devices and perform the following functions:

• set the AS values for the routing instance

• create confederations of group-managed devices

• create BGP peer groups

• create peers within the BGP peer groups

• retrieve statistical information

• monitor BGP-related network events

BGP routing information is not typically monitored by these systems because of the high volume of BGP and MP-BGP routes,

The CPAM discovers and monitors BGP routing information by consolidating the data from the CPAAs and providing an overview of a carrier network. You can use the information to, for example, monitor whether the change in the number of BGP routes may compromise the stability of the network, or if key BGP routes are disappearing. For VPRN routes, a high rate of change for a set of VRFs is flagged by the CPAM.

Note: The number of routes sent out for an RT from a PE is captured by the CPAA MP-BGP. The CPAM displays the number of routes and exported routes for a VRF.

The CPAM and the CPAA use peering sessions, originator IDs and next hops in the advertised routes to detect BGP speakers. The CPAM is aware of the NFM-P-managed routers that are running BGP.

BGP and the CPAA

You can specify the role of a CPAA: IGP, BGP, or both. The role of the CPAA indicates to the CPAM whether information from a protocol should be interpreted. A CPAA with an IGP role must be assigned to an IGP administrative domain. A CPAA with a BGP role must be assigned to a BGP AS. See CPAM administrative domains for information.

The CPAA monitors a BGP AS and maintains a BGP RIB that is used by the CPAM to extract BGP route information. The CPAA supports the following BGP configurations:

• BGP AS

• BGP confederation AS

• BGP sub-AS

The CPAA does not send route updates to its peers or forward data traffic. The CPAA maintains a route table for all of the known routes. The CPAA should not function as a route reflector. In addition, EBGP peering is blocked. BGP is restricted to the core routing instance because services cannot be configured on the CPAA.

The CPAA should be peered with all of the route reflectors or with all of the IBGP speakers (full mesh topology) of the BGP AS or BGP sub-AS. See BGP topologies in CPAM for information about the deployment of the CPAA in supported topologies.

Note: Nokia recommends that the CPAA establish an IBGP connection with the BGP speakers, not the route reflector, because the route reflector advertises only one preferred next-hop.

CPAM administrative domains

WARNING Equipment Damage

The IGP administrative domain should generally be public IP address spaces, not private IP address spaces. If two IGP administrative domains have duplicate router IDs, for example, some functionality—such as the IP path monitor and managed routes—may not work correctly.

An administrative domain is a user-configured grouping that represents a logical routed network. The CPAM supports the following administrative domains:

• IGP administrative domain

  A routed network with OSPF, ISIS, or both protocols running. There can be only one backbone domain for each protocol. For OSPF, multiple areas with the same area ID cannot exist.

• BGP AS

  An administrative domain which represents the standard BGP AS, confederation AS, or sub-AS. A BGP confederation AS administrative domain contains other BGP sub-ASs.

An IGP administrative domain is uniquely identified by a domain number and name that are configured when it is created. A CPAA that is configured with an IGP role must be assigned to an IGP administrative domain. Each CPAA can be assigned to only one IGP administrative domain. A BGP AS is identified by a BGP AS number, which should be identical to the network-configured BGP AS, a BGP AS name, and BGP AS type. Each BGP AS administrative domain is associated with only one IGP administrative domain. An IGP administrative domain can be associated with several BGP AS administrative domains. A CPAA that is configured with a BGP role must be assigned to each BGP AS administrative domain. Each CPAA can be assigned to only one BGP AS administrative domain.

The BGP AS administrative domain in the CPAM models the actual BGP AS that is being monitored by a CPAA with a BGP role. One CPAA is used to monitor BGP routes in each AS or sub-AS, that is associated with an IGP administrative domain in the CPAM. The following types of BGP AS are monitored:

• standard BGP AS

• BGP sub-AS (within a confederation AS)

A standard BGP AS uses a registered BGP AS identifier to advertise its known BGP routes to other registered AS domains.

A BGP sub-AS can exist within a confederation AS administrative domain and uses a private AS identifier to advertise routes to other BGP sub-AS domains within the registered AS. The use of sub-AS domains reduces the number of IBGP sessions between routers and the number of BGP routes advertised between registered AS domains. Confederations do not reduce the number of updates between the ASs.

BGP sub-AS administrative domains are created in the CPAM within a confederation AS. A standard AS uses a CPAA to monitor the entire AS. For BGP confederation AS domains, each sub-AS domain should be monitored using a different CPAA.

MP-BGP

The CPAA collects MP-BGP routing information when the VPN IPv4 address family is activated on each IBGP peering session. The CPAA uses the RT of the advertised routes to differentiate between the VPN sites. Although a VPN site can be assigned more than one RT, the CPAA cannot make this association from the routing updates. The next hops in the advertised routes identify the PEs for the specific RT.

You can use the CPAM to retrieve MP-BGP information, such as the number of routes per RT. In addition, you can retrieve the list of next hops and number of routes per next hop for each RT. The CPAA monitors the number of routes for each RT and, if you configure threshold reaching alarms, raises alarms when the number of routes reaches the configured threshold, such as low water mark, high water mark, and flap rate.

BGP RIB information

You can use the CPAM to view BGP attribute information about BGP advertised prefixes. The CPAA collects the following BGP RIB information, that can be viewed in the CPAM:

• routes with the same advertised BGP next hop

• routes that share the same route reflector originator ID (originator of the route into the AS)

• routes with the same MED

• IBGP routes with the same local preference attribute

• routes with the same BGP communities attribute

BGP AS path view

The BGP AS path view is an on-demand graphical representation of the entire BGP network from the perspective of a BGP AS or sub-AS, as displayed in the figure below. Because only one CPAA can be associated with a BGP AS, the BGP AS path view displays the BGP network from the perspective of one CPAA. A BGP AS or sub-AS is represented as a node on the topology map.

Figure 10-1: BGP AS path view

Each arrow represents at least one EBGP connection between two BGP ASs or sub-ASs and indicates the direction of EBGP update message from the originating AS to the terminating AS. Each link on the map displays the number of EBGP routes that are advertised from one AS to another AS, in the direction indicated by the arrow.

You can specify the number of ASs and next hops that are displayed on the map, as described in To view BGP AS path topology .

You can view the information displayed on the BGP AS path view from the ASN and ASN link forms. See To view ASN link information to To view BGP AS path topology for information.

BGP highlighting

You can use the CPAM to highlight all of the NEs that advertise a prefix into an AS on the IGP topology map. You must specify a BGP prefix, and an RD for VPN IPv4 prefixes. The CPAM highlights all of the NEs that advertise a route for that prefix into the administrative domain. The router or routers which advertise the preferred route, based on the BGP attributes, are highlighted in a different color from the other advertising routers. See To highlight advertising routers for BGP prefixes for information about how to configure the highlighting of advertising routers that advertise prefixes into an AS or sub-AS.

© 2024 Nokia. Nokia Confidential Information

Use subject to agreed restrictions on disclosure and use.