BGP Configuration Guide for Cisco 8000 Series Routers, Cisco IOS XR Releases

Store and analyze changes in the prefixes received from BGP peer

Updated: February 28, 2026

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Overview

How you use this feature
Verify the BGP prefix statistics

Overview

Explains BGP prefix statistics features and offers instructions to verify and analyze prefix data to enhance routing visibility and diagnostic capabilities.

The store and analyze changes in the prefixes received from BGP peer is a serviceability feature that

allow routers to handle analysis of millions of BGP paths across IPv4 and IPv6 address families,
enables operators to actively monitor and analyze changes, acceptances, and rejections of prefixes received from BGP peers by providing detailed statistics, and
allows you to store all original copies of routes received from peers, including those not selected as the best path.

This feature helps you improve serviceability by monitoring BGP operations and facilitating debugging in both production and lab environments.

Table 1. Feature History Table
Feature Name	Release Information	Feature Description
Store and analyze changes in the prefixes received from BGP peer	Release 25.4.1	Introduced in this release on: Fixed Systems (8010 [ASIC: A100])(select variants only) This feature is now supported on: 8011-32Y8L2H2FH 8011-12G12X4Y-A 8011-12G12X4Y-D
Store and analyze changes in the prefixes received from BGP peer	Release 25.1.1	Introduced in this release on: Fixed Systems (8010 [ASIC: A100])(select variants only) This feature is supported on Cisco 8011-4G24Y4H-I routers.
Store and analyze changes in the prefixes received from BGP peer	Release 24.4.1	Introduced in this release on: Fixed Systems (8200 [ASIC: P100], 8700 [ASIC: P100, K100])(select variants only); Modular Systems (8800 [LC ASIC: P100])(select variants only) Improve serviceability and troubleshoot BGP operations effectively by monitoring changes in prefixes received from BGP peers. This feature allows routers to store all original routes from peers, including non-best paths, for both IPv4 and IPv6. It provides detailed statistics on accepted, modified, and denied prefixes. By enabling assessment of inbound policies without network disruption and supporting soft reconfiguration to store all route updates, it simplifies debugging and policy adjustments in production and lab environments. This feature is supported on: 8212-48FH-M 8711-32FH-M 8712-MOD-M 88-LC1-36EH 88-LC1-12TH24FH-E 88-LC1-52Y8H-EM

How you use this feature

Soft reconfiguration stores incoming prefixes before applying policies if the peer does not support route refresh; using the always keyword forces storage even when route refresh is supported.
The soft reconfiguration inbound always command enables storage of all updates from a specified neighbor.
The soft reconfiguration inbound command stores the original unmodified route alongside modified or filtered routes, allowing you to perform a “soft clear” after inbound policy changes.
Prefixes fall into three categories: accepted and unmodified, accepted and modified, or denied.
Operators can monitor the impact of inbound policies without network disruption, helping to maintain stability and facilitate troubleshooting.

Verify the BGP prefix statistics

Ensure that you verify the soft reconfiguration statistics and evaluate the impact of inbound policies on IPv4 unicast BGP sessions to maintain proper routing behavior and policy compliance.

Before you begin

Confirm that BGP is configured and that soft reconfiguration is enabled on the relevant neighbors.
Verify that you know the IP addresses of BGP neighbors and the inbound policies applied.
Be aware that soft reconfiguration is memory intensive; ensure the router has sufficient resources.
Understand that the soft-reconfiguration inbound command stores updates from neighbors, enabling soft resets even if the neighbor does not support route refresh.

Procedure

Use the show bgp ipv4 unicast summary soft-reconfig-stats command to verify the soft reconfiguration statistics for IPv4 unicast BGP sessions.

Example:

Router# show bgp ipv4 unicast summary soft-reconfig-stats

....
.....

Neighbor     Spk  AS  MsgRcvd MsgSent TblVer InQ  OutQ  Up/Down     St/PfxRcd  SoftChgd  Denied
10.10.10.4    0   3    15       12      0    0     0    00:46:06 2           0       0
Total                                                            2           0       0

Legend:

Total PfxRcd: Sum of accepted unmodified and modifed paths
Total SoftChgd: Sum of accepted modified paths
Total Denied: Sum of Denied paths

This output displays the soft reconfiguration statistics for IPv4 unicast BGP sessions given below:

Total PfxRcd represents the sum of accepted unmodified and modified paths.
Total SoftChgd represents the sum of accepted modified paths.
Total Denied represents the sum of denied paths.

Use the show bgp ipv4 unicast neighbors dryrun-policy pass command to verify the dry run policy impact on inbound policy.

Example:

Router# show bgp ipv4 unicast neighbors 10.10.10.1 dryrun-policy pass

Sat Oct 14 01:22:02.946 EDT

Policy Statistics
-----------------
     AFI:                          IPv4 Unicast
     Direction:                    Inbound
     In-use Policy:                pass                
     Dry-run Policy:               pass  
     Remote-as:                    300   
     Total Networks walked:        257   
     Total Paths walked:           72257 
     Dry Run elapsed time(ms):     8         
----------------------------------------------------------------------------------------
                                        Dry-run-Policy      In-use-Policy      Delta      
----------------------------------------------------------------------------------------
Neighbor: 10.10.10.1      
     Accepted Unmodified:               257                 257                 0         
     Accepted Modified:                 0                   0                   0         
     Pre-inbound policy copy:           0                   0                   0         
     Denied:                            0                   0                   0         
     Estimated Total Paths Memory:      26.10KB             26.10KB             0.00      
----------------------------------------------------------------------------------------
    /* The values in the table provides information confirms that the BGP session with the 
       neighbor 10.10.10.1 is passing the dry run policy. 
       The values indicates that the BGP updates from the neighbor comply with the specified policies 
       without actually applying the policies. The values in the table provides insight into potential 
       routing changes without committing the policies. */

The table values confirm that the BGP session with neighbor 10.10.10.1 is successfully passing the dry run policy. This indicates that BGP updates from the neighbor comply with the specified policies without actually applying them. These values provide insight into potential routing changes without committing the policies, enabling you to evaluate policy impact safely.

Use the show bgp scale detail command to verify the statistics on configured and established neighbors, and address-family prefixes, paths, and memory usage.

Example:

Router# show bgp scale detail
Fri Feb 2 12:49:38.349 EST

VRF: default
Neighbors Configured: 2 Established: 2

Address-Family  Prefixes  Paths  PathElem  Prefix       Path      PathElem    
                                           Memory       Memory    Memory

IPv4 Unicast    3          5        3      564.00       520.00    369.00

SoftReconfig Changed  1  104.00 ---> This field shows that soft reconfiguration has been enabled. It also displays the number of prefixes that were accepted and modified, and the amount of memory consumed by the prefix. 
------------------------------------------------------------------------------
Total           3          5        3      564.00       520.00    369.00

Total VRFs Configured: 0

The field SoftReconfig Changed 1 104.00 indicates that soft reconfiguration is enabled. It also shows the number of prefixes that were accepted and modified, along with the memory consumed by these prefixes, providing insight into resource usage related to soft reconfiguration.

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