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Suppress BGP Advertisement for Inactive Routes

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Suppress BGP Advertisement for Inactive Routes

Contents

How to Configure BGP to Suppress Advertisement for Inactive Routes

Suppressing Inactive Route Advertisement

Suppressing Inactive Route Advertisement to Provide More Consistent Data Forwarding

Prerequisites

Restrictions

Displaying Inactive Routes

Configuration Examples for BGP Inactive Route Advertisement Suppression

Configuring the Suppression of Inactive Route Advertisement: Example

Displaying Inactive Routes: Example

Additional References

Related Documents

Standards

MIBs

RFCs

Technical Assistance

Command Reference

bgp suppress-inactive

show ip bgp rib-failure


Suppress BGP Advertisement for Inactive Routes

The Suppress BGP Advertisements for Inactive Routes features allows you to configure the suppression of advertisements for routes that are not installed in the Routing Information Base (RIB). Configuring this feature allows Border Gateway Protocol (BGP) updates to be more consistent with data used for traffic forwarding.

Feature History for the Suppress BGP Advertisement for Inactive Routes Feature

Release
Modification

12.2(25)S

This feature was introduced.


Finding Support Information for Platforms and Cisco IOS Software Images

Use Cisco Feature Navigator to find information about platform support and Cisco IOS software image support. Access Cisco Feature Navigator at http://www.cisco.com/go/fn. You must have an account on Cisco.com. If you do not have an account or have forgotten your username or password, click Cancel at the login dialog box and follow the instructions that appear.

Contents

•How to Configure BGP to Suppress Advertisement for Inactive Routes

•Configuration Examples for BGP Inactive Route Advertisement Suppression

•Additional References

•Command Reference

How to Configure BGP to Suppress Advertisement for Inactive Routes

This section contains the following tasks:

•Suppressing Inactive Route Advertisement

•Displaying Inactive Routes

Suppressing Inactive Route Advertisement

In Cisco IOS software, a BGP routing process can advertise routes that are not installed in the RIB to BGP peers by default. A route that is not installed into the RIB is an inactive route. Inactive route advertisement can occur, for example, when routes are advertised through common route aggregation.

Entering the bgp suppress-inactive command configures BGP to not advertise inactive routes to any BGP peer. The no form of this command is used to enable inactive route advertisement.

Suppressing Inactive Route Advertisement to Provide More Consistent Data Forwarding

Inactive route advertisements can be suppressed to provide more consistent data forwarding. This feature can be configured on a per IPv4 address family basis. For example, when configuring maximum number of routes that can be configured in a VRF with the maximum routes global configuration command, you also suppress inactive route advertisement to prevent inactive routes from being accepted into the VRF after route limit has been exceeded.

Prerequisites

This document assumes that BGP is enabled and peering has been established.

Restrictions

Inactive route suppression can be configured only under the IPv4 address family or under a default IPv4 general session.

SUMMARY STEPS

1. enable

2. configure terminal

3. router bgp as-number

4. address-family {ipv4 [multicast | unicast [vrf vrf-name] | vrf vrf-name] | ipv6 [multicast | unicast] | vpnv4 [unicast]}

5. bgp suppress-inactive

6. end

DETAILED STEPS

 
Command or Action
Purpose

Step 1 

enable

Example:

Router> enable

Enables privileged EXEC mode.

•Enter your password if prompted.

Step 2 

configure terminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3 

router bgp as-number

Example:

Router(config)# router bgp 65535

Enters router configuration mode, and creates a BGP routing process.

Step 4 

address-family {ipv4 [multicast | unicast [vrf vrf-name] | vrf vrf-name] | ipv6 [multicast | unicast] | vpnv4 [unicast]}

Example:

Router(config-router-af)# address-family ipv4 unicast

Enter address family configuration mode to configure BGP peers to accept address family specific configurations.

•The example creates an IPv4 unicast address family session.

Step 5 

bgp suppress-inactive

Example:

Router(config-router-af)# bgp suppress-inactive

Exits address-family configuration mode, and enters Privileged EXEC mode.

•BGP advertises inactive routes by default.

•Entering the no form of this command enables the advertisement of inactive routes.

Step 6 

end

Example:

Router(config-extcom-list)# end

Exits address-family configuration mode and enters privileged EXEC mode.

Displaying Inactive Routes

BGP routes that were not installed in the RIB can be displayed by entering the show ip bgp rib-failure command in EXEC mode.

SUMMARY STEPS

1. show ip bgp rib-failure

DETAILED STEPS

 
Command or Action
Purpose

Step 1 

show ip bgp rib-failure

Example:

Router> show ip bgp rib-failure

Displays BGP routes that are not installed in the RIB.

Configuration Examples for BGP Inactive Route Advertisement Suppression

The following examples show how to configure and verify this feature:

•Configuring the Suppression of Inactive Route Advertisement: Example

•Displaying Inactive Routes: Example

Configuring the Suppression of Inactive Route Advertisement: Example

The following example, starting in global configuration mode, configures BGP to not advertise inactive routes: 

Router(config)# router bgp 50000

Router(config-router)# address-family ipv4 unicast

Router(config-router-af)# bgp suppress-inactive 

Router(config-router-af)# end

The following example configures a maximum route limit in the VRF named red and configures BGP to not advertise inactive routes through the VRF named RED: 

Router(config)# ip vrf RED 

Router(config-vrf)# rd 50000:10

Router(config-vrf)# maximum routes 1000 10 

Router(config-vrf)# exit

Router(config)# router bgp 50000

Router(config-router)# address-family ipv4 vrf RED

Router(config-router-af)# bgp suppress-inactive 

Router(config-router-af)# end

Displaying Inactive Routes: Example

The following example uses the show ip bgp rib-failure Exec command to display routes that are not installed in the RIB. The output shows that the displayed routes were not installed because a route or routes with a better administrative distance already exist in the RIB. 

Router# show ip bgp rib-failure 

Network            Next Hop                      RIB-failure   RIB-NH Matches

10.1.15.0/24       10.1.35.5           Higher admin distance              n/a

10.1.16.0/24       10.1.15.1           Higher admin distance              n/a

Additional References

The following sections provide references related to Suppress BGP Advertisement for Inactive Routes.

Related Documents

Related Topic
Document Title

BGP commands

•Cisco IOS IP Command Reference, Volume 2 of 4: Routing Protocols, Release 12.3T

BGP configuration tasks

•Cisco IOS IP Configuration Guide, Release 12.3


Standards

Standards
Title

No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature.

—


MIBs

MIBs
MIBs Link

No new or modified MIBs are supported by this feature, and support for existing MIBs has not been modified by this feature.

To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL:

http://www.cisco.com/go/mibs


RFCs

RFCs
Title

No new or modified RFCs are supported by this feature, and support for existing standards has not been modified by this feature.

—


Technical Assistance

Description
Link

Technical Assistance Center (TAC) home page, containing 30,000 pages of searchable technical content, including links to products, technologies, solutions, technical tips, tools, and lots more. Registered Cisco.com users can log in from this page to access even more content.

TAC Home Page:

http://www.cisco.com/public/support/tac/home.shtml

BGP Support Page:

http://www.cisco.com/en/US/partner/tech/tk365/tk80/tsd_technology_support_sub-protocol_home.html


Command Reference

This section documents modified commands.

•bgp suppress-inactive

•show ip bgp rib-failure

bgp suppress-inactive

To suppress the advertisement of routes that are not installed in the routing information base (RIB), use the bgp suppress-inactive command in address family or router configuration mode.

bgp suppress-inactive

no bgp suppress inactive

Syntax Description

This command has no arguments or keywords.

Defaults

No default behavior or values

Command Modes

Address family configuration
Router configuration

Command History

Release
Modification

12.2(11)T

This command was introduced.

12.0(26)S

This command was integrated into Cisco IOS Release 12.0(26)S.

12.2(25)S

This command was integrated into Cisco IOS Release 12.2(25)S.


Usage Guidelines

The bgp suppress-inactive command is used to prevent routes that are not installed in the RIB (inactive routes) from being advertised to peers. If this feature is not enabled or if the no form of this command is used, Border Gateway Protocol (BGP) will advertise inactive routes.

Note BGP marks routes that are not installed into the RIB with a RIB-failure flag. This flag will also appear in the output of the show ip bgp command; for example, Rib-Failure (17). This flag does not indicate an error or problem with the route or the RIB, and the route may still be advertised depending on the configuration of this command. Enter the show ip bgp rib-failure command to see more information about the inactive route.

Examples

In the following example, the BGP routing process is configured to not advertise routes that are not installed in the RIB: 

Router(config)# router bgp 500000 

Router(config-router)# address-family ipv4

Router(config-router)# bgp suppress-inactive

Related Commands

Command
Description

clear ip bgp

Resets a BGP connection or session.

show ip bgp rib-failure

Displays Border Gateway Protocol (BGP) routes that failed to install in the Routing Information Base (RIB) table.


show ip bgp rib-failure

To display Border Gateway Protocol (BGP) routes that failed to install in the Routing Information Base (RIB) table, use the show ip bgp rib-failure command in EXEC mode.

show ip bgp rib-failure

Syntax Description

This command has no keywords or arguments.

Command Modes

EXEC

Command History

Release
Modification

12.3

This command was introduced.

12.0(26)S

This command was integrated into Cisco IOS Release 12.0(26)S.

12.2(25)S

This command was integrated into Cisco IOS Release 12.2(25)S.


Examples

The following is sample output from the show ip bgp rib-failure command: 

Router# show ip bgp rib-failure 


Network            Next Hop                      RIB-failure   RIB-NH Matches

10.1.15.0/24       10.1.35.5           Higher admin distance              n/a

10.1.16.0/24       10.1.15.1           Higher admin distance              n/a

Table 1 describes the significant fields shown in the display.

Table 1 show ip bgp rib-failure Field Descriptions 

Field
Description

Network

IP address of a network entity.

Next Hop

IP address of the next system that is used when forwarding a packet to the destination network. An entry of 0.0.0.0 indicates that the router has some non-BGP routes to this network.

RIB-failure

Cause of RIB failure. Higher admin distance means that a route with a better (lower) administrative distance such as a static route already exists in the IP routing table.

RIB-NH Matches

Route status that applies only when Higher admin distance appears in the RIB-failure column and bgp suppress-inactive is configured for the address family being used. There are three choices:

•Yes—Means that the route in the RIB has the same nexthop as the BGP route or nexthop recurses down to the same adjacency as the BGP nexthop.

•No—Means that the nexthop in the RIB recurses down differently from the nexthop of the BGP route.

•n/a—Means that bgp suppress-inactive is not configured for the address family being used.


Related Commands

Command
Description

bgp suppress-inactive

Configures a router to suppress the advertisement of BGP routes that are not installed into the Routing Information Base (RIB) and Forwarding Information Base (FIB) tables

clear ip bgp

Resets a BGP connection or session.

neighbor soft-reconfiguration

Configures the Cisco IOS software to start storing updates.


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