A common route aggregation practice is to group as large an address space as possible into as few prefix entries as possible. This is desirable in reducing the number of prefixes carried by the Internet, but it's detrimental to adjacent networks that have multiple connections to the aggregating network. One result of aggregation is that routing accuracy of neighbors is lost.
In this situation, more-specific routes can be generated to better identify a prefix's address subsets across multiple connections. Deaggregation is a BGP feature that reconstructs components from a received aggregate prefix.
Deaggregation is accomplished by using the conditional injection feature. Conditional injection is the creation of more-specific components when an aggregate exists. These components are injected into the local BGP RIB to provide more-specific routing information in the local AS than the aggregate. These components can be installed in the IP RIB and advertised to other BGP peers within the AS.
Conditional route injection is configured as follows:
bgp inject-map map1 exist-map map2 [copy-attributes]
BGP tracks the prefix (the aggregate) in the exist-map to determine whether to install a prefix or prefixes as specified in the inject-map.
The exist-map must have at least two match clauses:
- match ip address prefix-list specifies the aggregate based on which to inject more specifics. Only one exact match is allowed.
- match ip route-source specifies the neighbor that sent the aggregate. The component inherits the attributes from the aggregate if the option copy-attributes is specified; otherwise, they are treated as locally generated routes for some of the attributes. The NEXT_HOP is always the eBGP peer that originated the aggregate. Additional matches can be made for AS_PATH and community.
from: Cisco IOS IP Routing: BGP Command Reference
Files:
Topology
Configs
BGP Configuration
BGP Conditional Route Injection
Feature HistoryThis feature module describes the BGP Conditional Route Injection feature. It includes the following sections:Feature Overview
Routes that are advertised through the Border Gateway Protocol (BGP) are commonly aggregated to minimize the number of routes that are used and reduce the size of global routing tables. However, common route aggregation can obscure more specific routing information that is more accurate but not necessary to forward packets to their destinations. Routing accuracy is obscured by common route aggregation because a prefix that represents multiple addresses or hosts over a large topological area cannot be accurately reflected in a single route. Cisco IOS software provides several methods in which you can originate a prefix into BGP. The existing methods include redistribution and using the network or aggregate-address command. These methods assume the existence of more specific routing information (matching the route to be originated) in either the routing table or the BGP table.The BGP Conditional Route Injection feature allows you to originate a prefix into a BGP routing table without the corresponding match. This feature allows more specific routes to be generated based on administrative policy or traffic engineering information in order to provide more specific control over the forwarding of packets to these more specific routes, which are injected into the BGP routing table only if the configured conditions are met. Enabling this feature will allow you to improve the accuracy of common route aggregation by conditionally injecting or replacing less specific prefixes with more specific prefixes. Only prefixes that are equal to or more specific than the original prefix may be injected. The BGP Conditional Route Injection feature is enabled with the bgp inject-map exist-mapcommand. This command uses two route maps (inject-map and exist-map) to install one (or more) more specific prefix into a BGP routing table. The exist-map specifies the prefixes that the BGP speaker will track. The inject-map defines the prefixes that will be created and installed into the local BGP table.Benefits
The BGP Conditional Route Injection feature allows you to inject more specific prefixes into a BGP routing table over less specific prefixes that were selected through normal route aggregation. These more specific prefixes can be used to provide a finer granularity of traffic engineering or administrative control than is possible with aggregated routes.Related Features and Technologies
The BGP Conditional Route Injection feature is an extension of the BGP routing protocol. For more information about configuring BGP, conditional advertisement, route summarization and route filtering, refer to the "Configuring BGP" chapter of the Release 12.2 Cisco IOS IP Configuration Guide and the Cisco IOS IP Command Reference, Volume 2 of 3: Routing Protocols.Supported Platforms
The BGP Conditional Route Injection feature is supported by all platforms in Cisco IOS Release 12.2(14)S that support BGP:•Cisco 7200 series
••Determining Platform Support Through Cisco Feature NavigatorCisco IOS software is packaged in feature sets that support specific platforms. To get updated information regarding platform support for this feature, access Cisco Feature Navigator. Cisco Feature Navigator dynamically updates the list of supported platforms as new platform support is added for the feature.Cisco Feature Navigator is a web-based tool that enables you to determine which Cisco IOS software images support a specific set of features and which features are supported in a specific Cisco IOS image. You can search by feature or release. Under the release section, you can compare releases side by side to display both the features unique to each software release and the features in common.To access Cisco Feature Navigator, you must have an account on Cisco.com. If you have forgotten or lost your account information, send a blank e-mail to cco-locksmith@cisco.com. An automatic check will verify that your e-mail address is registered with Cisco.com. If the check is successful, account details with a new random password will be e-mailed to you. Qualified users can establish an account on Cisco.com by following the directions athttp://www.cisco.com/register.Cisco Feature Navigator is updated regularly when major Cisco IOS software releases and technology releases occur. For the most current information, go to the Cisco Feature Navigator home page at the following URL:Availability of Cisco IOS Software ImagesPlatform support for particular Cisco IOS software releases is dependent on the availability of the software images for those platforms. Software images for some platforms may be deferred, delayed, or changed without prior notice. For updated information about platform support and availability of software images for each Cisco IOS software release, refer to the online release notes or, if supported, Cisco Feature Navigator.Supported Standards, MIBs, and RFCs
StandardsNo new or modified standards are supported by this feature.MIBsNo new or modified MIBs are supported by this feature.To obtain lists of supported MIBs by platform and Cisco IOS release, and to download MIB modules, go to the Cisco MIB website on Cisco.com at the following URL:RFCsNo new or modified RFCs are supported by this feature.Configuration Tasks
This section contains configuration tasks for the BGP Conditional Route Injection feature. The first task must be performed to implement conditional route injection for BGP, the second task is an optional task to help you verify that conditional route injection is configured and working. The second task includes some troubleshooting tips.Configuring BGP Conditional Route Injection
To configure the BGP Conditional Route Injection feature, perform the following required steps beginning in global configuration mode:
Note
Verifying BGP Conditional Route Injection
Use the optional show ip bgp or show ip bgp injected-paths commands to help you verify that BGP conditional route injection is configured and working. This task includes some troubleshooting tips.The following sample output is similar to the output that will be displayed when the show ip bgp command is entered:Router# show ip bgp 172.16.0.0BGP routing table entry for 172.16.0.0/8, version 13Paths:(2 available, best #1, table Default-IP-Routing-Table)Flag:0x200Not advertised to any peerLocal, (injected path from 172.16.0.0/8)10.0.0.2 from 10.0.0.2 (2.2.2.2)Origin incomplete, localpref 100, valid, external, bestCommunity:95787423120010.0.0.2 from 10.0.0.2 (2.2.2.2)Origin incomplete, metric 0, localpref 100, valid, externalThe following sample output is similar to the output that will be displayed when the show ip bgp injected-routescommand is entered:Router# show ip bgp injected-pathsBGP table version is 11, local router ID is 10.0.0.1Status codes:s suppressed, d damped, h history, * valid, > best, i -internalOrigin codes:i - IGP, e - EGP, ? - incompleteNetwork Next Hop Metric LocPrf Weight Path*> 172.16.0.0 10.0.0.2 0 ?*> 172.17.0.0/16 10.0.0.2 0 ?Troubleshooting TipsThe BGP Conditional Route Injection feature is based on the injection of a more specific prefix into the BGP routing table when a less specific prefix is present. If conditional route injection is not working properly, check the following:•••••Monitoring and Maintaining BGP Conditional Route Injection
To display BGP conditional advertisement information, use the following commands in EXEC mode, as needed:Configuration Examples
This following configuration example configures conditional route injection for the inject-map named ORIGINATE and the exist-map named LEARNED_PATH:router bgp 109bgp inject-map ORIGINATE exist-map LEARNED_PATH!route-map LEARNED_PATH permit 10match ip address prefix-list ROUTEmatch ip route-source prefix-list ROUTE_SOURCE!route-map ORIGINATE permit 10set ip address prefix-list ORIGINATED_ROUTESset community 14616:555 additive!ip prefix-list ROUTE permit 10.1.1.0/24!ip prefix-list ORIGINATED_ROUTES permit 10.1.1.0/25ip prefix-list ORIGINATED_ROUTES permit 10.1.1.128/25!ip prefix-list ROUTE_SOURCE permit 10.2.1.1/32Command Reference
This section documents new and modified commands. All other commands used with this feature are documented in the Cisco IOS Release 12.2 command reference publications.New CommandsModified Commandsbgp inject-map exist-map
To inject a more specific route into a Border Gateway Protocol (BGP) routing table, use the bgp inject-map exist-map command in address family or router configuration mode. To disable the conditional injection of a selected route, use the no form of this command.bgp inject-map {inject-map-name} exist-map {exist-map-name}[copy-attributes]no bgp inject-map {inject-map-name} exist-map {exist-map-name}[copy-attributes]Syntax Description
Defaults
The BGP Conditional Route Injection feature is not enabled by default.Command Modes
Address family configurationRouter configurationCommand History
Usage Guidelines
If the copy-attributes keyword is not specified when the bgp inject-map command is used, the components will use the default attributes for locally originated routes. If the copy-attribute keyword is used, the components will inherit the same attributes as the aggregate route.To enable conditional route injection, the exist-map must contain both the match ip address prefix-list and match ip route-source prefix-list match clauses in the route map paragraph.Examples
The following example configures the router for conditional route injection:(config-router)# bgp inject-map map1 exist-map map2 copy-attributesRelated Commands
show ip bgp
To display entries in the Border Gateway Protocol (BGP) routing table, use the show ip bgp command in EXEC command.show ip bgp [network] [network-mask] [longer-prefixes] [prefix-list prefix-list-name | route-map route-map-name] [shorter prefixes mask-length]Syntax Description
Command Modes
EXECCommand History
Examples
The following is sample output from the show ip bgp command in EXEC mode:Router# show ip bgpBGP table version is 5, local router ID is 10.0.33.34Status codes: s suppressed, d damped, h history, * valid, > best, i - internalOrigin codes: i - IGP, e - EGP, ? - incompleteNetwork Next Hop Metric LocPrf Weight Path*> 10.1.0.0 0.0.0.0 0 32768 ?* 10.2.0.0 10.0.33.35 10 0 35 ?*> 0.0.0.0 0 32768 ?* 10.0.0.0 10.0.33.35 10 0 35 ?*> 0.0.0.0 0 32768 ?*> 192.168.0.0/16 10.0.33.35 10 0 35 ?Table 1 describes the significant fields shown in the display.The following is sample output from the show ip bgp command in EXEC mode when you specify the longer-prefixes keyword:Router# show ip bgp 10.92.0.0 255.255.0.0 longer-prefixesBGP table version is 1738, local router ID is 192.168.72.24Status codes: s suppressed, * valid, > best, i - internalOrigin codes: i - IGP, e - EGP, ? - incompleteNetwork Next Hop Metric LocPrf Weight Path*> 10.92.0.0 10.92.72.30 8896 32768 ?* 10.92.72.30 0 109 108 ?*> 10.92.1.0 10.92.72.30 8796 32768 ?* 10.92.72.30 0 109 108 ?*> 10.92.11.0 10.92.72.30 42482 32768 ?* 10.92.72.30 0 109 108 ?*> 10.92.14.0 10.92.72.30 8796 32768 ?* 10.92.72.30 0 109 108 ?*> 10.92.15.0 10.92.72.30 8696 32768 ?* 10.92.72.30 0 109 108 ?*> 10.92.16.0 10.92.72.30 1400 32768 ?* 10.92.72.30 0 109 108 ?*> 10.92.17.0 10.92.72.30 1400 32768 ?* 10.92.72.30 0 109 108 ?*> 10.92.18.0 10.92.72.30 8876 32768 ?* 10.92.72.30 0 109 108 ?*> 10.92.19.0 10.92.72.30 8876 32768 ?* 10.92.72.30 0 109 108 ?The following is sample output from the show ip bgp command in EXEC mode, showing information for prefix 10.0.0.0:Router# show ip bgp 10.0.0.0BGP routing table entry for 10.0.0.0/8, version 628Paths: (1 available, best #1)Advertised to peer-groups:ebgpAdvertised to non peer-group peers:172.30.232.162109 65000 297 701 80172.30.233.56 from 172.30.233.56 (172.19.185.32)Origin incomplete, localpref 100, valid, external, best, ref 2
Note
The following is sample output from the show ip bgp command in privileged EXEC mode when you specify theprefix-list keyword:Router# show ip bgp prefix-list ROUTEBGP table version is 39, local router ID is 10.0.0.1Status codes:s suppressed, d damped, h history, * valid, > best, i -internalOrigin codes:i - IGP, e - EGP, ? - incompleteNetwork Next Hop Metric LocPrf Weight Path*> 192.168.1.0 10.0.0.2 0 ?* 10.0.0.2 0 0 200 ?The following is sample output from the show ip bgp command in privileged EXEC mode when you specify theroute-map keyword:Router# show ip bgp route-map LEARNED_PATHBGP table version is 40, local router ID is 10.0.0.1Status codes:s suppressed, d damped, h history, * valid, > best, i -internalOrigin codes:i - IGP, e - EGP, ? - incompleteNetwork Next Hop Metric LocPrf Weight Path*> 192.168.1.0 10.0.0.2 0 ?* 10.0.0.2 0 0 200 ?The following is sample output from the show ip bgp command in privileged EXEC mode when you specify theshorter-prefixes keyword:Router# show ip bgp 172.16.0.0/16 shorter-prefixes 8*> 172.16.0.0 10.0.0.2 0 ?* 10.0.0.2 0 0 200 ?Related Commands
show ip bgp injected-paths
To display all the injected paths in the BGP routing table, use the show ip bgp injected-paths command in EXEC mode.show ip bgp injected-pathsSyntax Description
This command has no arguments or keywords.Command Modes
EXECCommand History
Examples
The following is sample output from the show ip bgp injected-paths command in EXEC mode:Router# show ip bgp injected-pathsBGP table version is 11, local router ID is 10.0.0.1Status codes:s suppressed, d damped, h history, * valid, > best, i -internalOrigin codes:i - IGP, e - EGP, ? - incompleteNetwork Next Hop Metric LocPrf Weight Path*> 172.16.0.0 10.0.0.2 0 ?*> 172.17.0.0/16 10.0.0.2 0 ?Table 2 describes the significant fields shown in the display.
Files:
Topology
Configs
BGP Configuration
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