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Table Of Contents
BGP 4 MIB Support for per-Peer Received Routes
BGP 4 per-Peer Received Routes Table Elements and Objects
Network Address Prefix Descriptions for the NLRI Field
Related Features and Technologies
BGP 4 MIB Support for per-Peer Received Routes
First Published: 12.0(21)SLast Updated: February 28, 2006History for the BGP 4 MIB Support for per-Peer Received Routes Feature
Finding Support Information for Platforms and Cisco IOS Software Images
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Feature Overview
BGP 4 MIB Support for per-Peer Received Routes introduces a new table in the CISCO-BGP4-MIB that provides the capability to query (by using Simple Network Management Protocol [SNMP] commands) for routes that are learned from individual Border Gateway Protocol (BGP) peers.
Before this new MIB table was introduced, a network operator could obtain the routes learned by a local BGP-speaking router by querying the local BGP speaker with an SNMP command (for example, the snmpwalk command). The network operator used the SNMP command to query the bgp4PathAttrTable of the CISCO-BGP4-MIB. The routes that were returned from a bgp4PathAttrTable query were indexed in the following order:
•
Prefix
•
•
Because the bgp4PathAttrTable indexes the prefixes first, obtaining routes learned from individual BGP peers will require the network operator to "walk through" the complete bgp4PathAttrTable and filter out routes from the interested peer. A BGP Routing Information Base (RIB) could contain 10,000 or more routes, which makes a manual "walk" operation impossible and automated walk operations very inefficient.
BGP 4 MIB Support for per-Peer Received Routes introduces a Cisco-specific enterprise extension to the CISCO-BGP4-MIB that defines a new table called the cbgpRouterTable. The cbgpRouterTable provides the same information as the bgp4PathAttrTable with the following two differences:
•
–
–
–
The search criteria for SNMP queries of local routes are improved because peer addresses are indexed before prefixes. A search for routes that are learned from individual peers is improved with this enhancement because peer addresses are indexed before prefixes. A network operator will no longer need to search through potentially thousands of routes to obtain the learned routes of a local BGP RIB table.
•
Note
BGP 4 per-Peer Received Routes Table Elements and Objects
The following sections describe new table elements, AFI and SAFI tables and objects, and network address prefixes in the Network Layer Reachability Information (NLRI) fields that have been introduced by the BGP 4 MIB Support for per-Peer Received Routes enhancement.
MIB Tables and Objects
Table 1 describes the MIB indexes of the cbgpRouterTable.
For a complete description of the MIB, see the CISCO-BGP4-MIB file CISCO-BGP4-MIB.my, available through Cisco.com at the following URL:
http://www.cisco.com/public/sw-center/netmgmt/cmtk/mibs.shtml
Table 1 MIB Indexes of the cbgpRouterTable
cbgpRouteAfi
Represents the AFI of the network layer protocol that is associated with the route.
cbgpRouteSafi
Represents the SAFI of the route. It gives additional information about the type of the route. The AFI and SAFI are used together to determine which local RIB (Loc-RIB) contains a particular route.
cbgpRoutePeerType
Represents the type of network layer address that is stored in the cbgpRoutePeer object.
cbgpRoutePeer
Represents the network layer address of the peer from which the route information has been learned.
cbgpRouteAddrPrefix
Represents the network address prefix that is carried in a BGP update message.
See Table 2 for information about the types of network layer addresses that can be stored in specific types of AFI and SAFI objects.
cbgpRouteAddrPrefixLen
Represents the length in bits of the network address prefix in the NLRI field.
See Table 3 for a description of the 13 possible entries.
AFIs and SAFIs
Table 2 lists the AFI and SAFI values that can be assigned to or held by the cbgpRouteAfi and cbgpRouteSafi indexes, respectively. Table 2 also displays the network address prefix type that can be held by specific combinations of AFIs and SAFIs. The type of network address prefix that can be carried in a BGP update message depends on the combination of AFIs and SAFIs.
Table 2 AFIs and SAFIs
ipv4(1)
unicast(1)
IPv4 address
ipv4(1)
multicast(2)
IPv4 address
ipv4(1)
vpn(128)
VPN-IPv4 address
ipv6(2)
unicast(1)
IPv6 address
Note
Network Address Prefix Descriptions for the NLRI Field
Table 3 describes the length in bits of the network address prefix in the NLRI field of the cbgpRouteTable. Each entry in the table provides information about the route that is selected by any of the six indexes in Table 1.
Benefits
Improved SNMP Query Capabilities
The search criteria for SNMP queries for routes that are advertised by individual peers are improved because the peer address is indexed before the prefix. A network operator will no longer need to search through potentially thousands of routes to obtain the learned routes of a local BGP RIB table.
Improved AFI and SAFI Support
Support is added for multiprotocol BGP. AFI and SAFI are added as indexes to the table. The CISCO-BGP4-MIB can be queried for any combination of AFIs and SAFIs that are supported by the local BGP speaker.
Restrictions
BGP 4 MIB Support for per-Peer Received Routes supports only routes that are contained in IPv4 AFIs and unicast SAFIs in the local BGP RIB table. The BGP 4 MIB Support for per-Peer Received Routes enhancement is supported only by BGP Version 4.
Related Features and Technologies
BGP 4 MIB Support for per-Peer Received Routes is an extension of the BGP routing protocol. For more information about configuring BGP, refer to the "Configuring BGP" chapter of the Cisco IOS Release 12.0 Network Protocols Configuration Guide, Part 1, and Cisco IOS Release 12.0 Network Protocols Command Reference, Part 1.
Additional References
The following sections provide references related to BGP 4 MIB Support for per-Peer Received Routes.
Related Documents
Configuring SNMP Support
The chapter "Configuring SNMP Support" in Cisco IOS Configuration Fundamentals Configuration Guide, Release 12.4
SNMP Commands
The chapter "SNMP Commands" in Cisco IOS Configuration Fundamentals Command Reference, Release 12.4
Standards
MIBs
None
To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL:
RFCs
RFC 1657
BGP-4 MIB
RFC 1771
A Border Gateway Protocol 4 (BGP-4)
RFC 2547
BGP/MPLS VPNs
RFC 2858
Multiprotocol Extensions for BGP-4
Technical Assistance
Configuration Tasks
None
Configuration Examples
None
Command Reference
None
Glossary
AFI—Address Family Identifier. Carries the identity of the network layer protocol that is associated with the network address.
BGP—Border Gateway Protocol. An interdomain routing protocol that exchanges reachability information with other BGP systems. It is defined by RFC 1163, A Border Gateway Protocol (BGP). The current implementation of BGP is BGP Version 4 (BGP4). BGP4 is the predominant interdomain routing protocol that is used on the Internet. It supports CIDR and uses route aggregation mechanisms to reduce the size of routing tables.
MBGP—multiprotocol BGP. An enhanced version of BGP that carries routing information for multiple network layer protocols and IP multicast routes. It is defined in RFC 2858, Multiprotocol Extensions for BGP-4.
MIB—Management Information Base. A group of managed objects that are contained within a virtual information store or database. MIB objects are stored so that values can be assigned to object identifiers and to assist managed agents by defining which MIB objects should be implemented. The value of a MIB object can be changed or retrieved using SNMP or CMIP commands, usually through a GUI network management system. MIB objects are organized in a tree structure that includes public (standard) and private (proprietary) branches.
NLRI—Network Layer Reachability Information. Carries route attributes that describe a route and how to connect to a destination. This information is carried in BGP update messages. A BGP update message can carry one or more NLRI prefixes.
RIB—Routing Information Base (RIB). A central repository of routes that contains Layer 3 reachability information and destination IP addresses or prefixes. The RIB is also known as the routing table.
SAFI—Subsequent Address Family Identifier. Provides additional information about the type of the Network Layer Reachability Information that is carried in the attribute.
SNMP—Simple Network Management Protocol. A network management protocol used almost exclusively in TCP/IP networks. SNMP provides a means to monitor and control network devices and to manage configurations, statistics collection, performance, and security.
snmpwalk—The snmpwalk command is a Simple Network Management Protocol (SNMP) application that is used to communicate with a network entity MIB using SNMP.
VPN—Virtual Private Network. Enables IP traffic to travel securely over a public TCP/IP network by encrypting all traffic from one network to another. A VPN uses a tunnel to encrypt all information at the IP level.
Any Internet Protocol (IP) addresses used in this document are not intended to be actual addresses. Any examples, command display output, and figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses in illustrative content is unintentional and coincidental.
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