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

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

BGP route advertisement synchronization

Updated: June 9, 2026

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Explains how BGP route advertisement synchronization ensures reliable route advertisements by validating hardware programming using synchronization marker and HW-ACK mechanisms, reducing transient traffic drops and aligning with operational requirements.

A BGP route advertisement synchronization feature is a protocol mechanism that

  • delays BGP route advertisements until the hardware forwarding plane is programmed and confirmed through the hardware acknowledgement (HW-ACK) message

  • uses the synchronizaton marker infrastructure as a synchronization checkpoint between software and hardware layers

  • protects against transient traffic drops and supports operational requirements in large-scale deployments.

The synchronization marker acts as a tracking object for batching route updates, while HW-ACK message confirms successful hardware programming, enabling scalable and reliable BGP route advertisement control.

BGP route advertisement synchronization operational impact and route control

Table 1. Feature History Table

Feature Name

Release

Description

BGP hardware-acknowledged route advertisement

 Release 26.2.1

Introduced in this release on: Fixed Systems (8200 [ASIC: Q100,Q200, P100], 8700 [ASIC: P100, K100], 8010 [ASIC: A100]);Centralized Systems (8600 [ASIC:Q200]) ; Modular Systems (8800 [LC ASIC: K100)]

This feature delays BGP route advertisement until routes are confirmed programmed in hardware, preventing traffic loss from premature advertising. It uses synchronization markers and hardware acknowledgments to ensure routes are only advertised after hardware installation, enhancing network stability and performance with minimal manual intervention.

BGP route advertisement synchronization regulates when BGP propagates new or changed routes to peers, linking route advertisement to hardware programming status for improved reliability and reduced convergence problems.

Key drivers for BGP route advertisement synchronization include:

  • preventing transient traffic drops by ensuring routers advertise routes only after hardware is ready to forward traffic

  • providing consistency in large-scale and multi-platform deployments by synchronizing BGP updates with the state of the forwarding plane

  • supporting critical customer requirements for deterministic convergence and improved interoperability

The main attributes of synchronization marker and HW-ACK message flow in BGP advertisement synchronization are as follows:

  1. BGP batches route updates and assigns a synchronization marker to each batch

  2. Routing Information Base (RIB) propagates the synchronization marker to all Forwarding Information Bases (FIBs), which then program the routes in hardware

  3. FIB generates hardware ACKs for the synchronization marker once hardware is programmed, and RIB returns acknowledgment to BGP when all FIBs have completed programming

BGP route advertisement synchronization and traditional route advertisement can be contrasted as follows:

Table 2. Traditional vs. Synchronized Advertisement

Traditional BGP Advertisement

BGP Advertisement Synchronization

forwards route advertisements before hardware programming confirmation

delays route advertisements until synchronization marker HW-ACK message is received

How BGP route advertisement synchronization works

BGP route advertisement synchronization is critical for high-reliability networks and helps avoid route advertisement before hardware readiness. The feature is especially important for operators that require smooth convergence, and is fully supported on Cisco 8000 Series platforms from Cisco IOS XR Release 26.2.1 onward.

Summary

BGP route advertisement synchronization aligns route advertisement and hardware programming to minimize the risk of transient traffic loss. The process ensures BGP advertises routes to peers only after successful hardware installation.

The key components involved in the process are:

  • BGP process: Collects route updates and initiates synchronization checkpoints called synchronization markers.

  • Routing Information Base (RIB): Manages synchronization markers, distributes them to hardware, and tracks acknowledgment status.

  • Forwarding Information Base (FIB) and OFA/NPU hardware: Programs routes into the hardware, signaling completion with HW-ACKs.

Workflow

The process stages describe how BGP, RIB, and FIB coordinate to ensure only hardware-programmed routes are advertised:

  1. BGP receives new route information and batches these updates, sending them to RIB with a SyncMarker. This marker acts as a synchronization checkpoint for a set of route updates.
    • BGP identifies routes to advertise and bundles them for processing efficiency.
    • Each batch sent to RIB includes a SyncMarker for tracking.
    This allows all routes in the batch to be tracked until hardware programming is complete. The result is a batch of routes associated with a SyncMarker for downstream hardware acknowledgment.
  2. RIB receives the route batch and SyncMarker, then distributes SyncMarker objects to all platform FIB instances, and tracks HW-ACK responses from each FIB.
    • RIB distributes synchronization markers to all FIBs.
    • RIB monitors HW-ACKs using SyncMarker IDs.
    This stage sets up checkpoints and prepares to collect hardware programming status. The result: FIBs are aware of the pending SyncMarker and begin programming the relevant routes.
  3. Each FIB instance (and underlying hardware) programs the new set of routes into hardware and prepares an HW-ACK event for the SyncMarker when programming is completed.
    • FIB programs each route in the batch.
    • After successful programming, FIB sends HW-ACK for the SyncMarker.
    Programming errors are retried; persistent issues are reported to upper layers. The result: Each FIB signals completion (HW-ACK) for its SyncMarker when programming is finished.
  4. FIB instances generate HW-ACKs upon completing hardware programming. RIB collects HW-ACKs from all participating FIBs for the relevant SyncMarker.
    • FIB sends HW-ACK after programming all routes for the SyncMarker.
    • RIB waits for HW-ACKs from all FIBs before continuing.
    RIB proceeds when all FIBs respond or after programmed timeouts; transient errors are contained. The result: RIB determines hardware programming status for the batch.
  5. After all HW-ACK responses are received, RIB signals to BGP that programming is complete for the batch. BGP can then advertise those routes to peers.
    • RIB signals SyncMarker completion to BGP.
    • BGP updates peer groups and sends advertisements for programmed routes.
    BGP does not advertise unacknowledged or failed routes, only successfully programmed ones. The result: Only routes confirmed as programmed are advertised, preserving network stability and scalability.

Result

BGP advertises routes to peers only after hardware programming is confirmed, minimizing transient traffic drops and providing operational reliability.

What’s next

For implementation details, see the process for configuring BGP route advertisement synchronization with the update wait-install command and refer to platform-specific operational and troubleshooting guidelines.

Configure BGP route advertisement synchronization

Configure BGP route advertisement synchronization to delay route advertisement until the route is fully programmed and acknowledged by the hardware forwarding plane.

  • Advertise routes only after hardware confirmation to prevent premature traffic handoff and reduce risk of transient traffic drops.

  • Enhance operational reliability and consistency for large-scale and critical deployments.

BGP route advertisement synchronization leverages the BGP route advertisement synchronization feature, integrating synchronization marker and hardware acknowledgment (HW-ACK) mechanisms to provide consistent route distribution.

Before you begin

Before you begin, verify these prerequisites:

  • BGP is enabled and address-family configuration is complete.

Follow these steps to configure BGP route advertisement synchronization with the update wait-install command.

Procedure

1.

Enter BGP configuration mode and add update wait-install command under the address-family requiring synchronization.

Example:


Router(config)# router bgp 100
Router(config-bgp)# bgp router-id 192.168.0.1
Router(config-bgp)# bgp graceful-restart
Router(config-bgp)# address-family vpnv4 unicast
Router(config-bgp-af)# vrf all
Router(config-bgp-af-vrf-all)# update wait-install
Router(config-bgp-af-vrf-all)# exit
Router(config-bgp-af)# neighbor-group ce_grp
Router(config-bgp-af)# exit
Router(config)# exit

Configure update wait-installcommand for each address-family needing route advertisement synchronization.

Additional keywords after wait-install command enable another existing feature which is not related to functionality of the BGP route advertisement synchronization feature.

BGP route advertisement synchronization is configured for the selected address-family.
2.

Verify that update wait-install is present under the relevant address-family in the running configuration.

Example:


Router# show running-config | include update wait-install

router bgp 100
 bgp router-id 192.168.0.1
 bgp graceful-restart
 address-family vpnv4 unicast
  vrf all
  !
  update wait-install
 !
 neighbor-group CE_GRP

Confirm that update wait-install is listed for each address-family where synchronization is required.

  • Ensure the command appears under the intended address-family.

Route synchronization feature is enabled and visible in the running configuration.
3.

Verify that the Routing Information Base (RIB) synchronization markers for the BGP client show no pending operations, acknowledgments have been received, and timing statistics indicate normal BGP route advertisement synchronization processing for all VRFs.

Example:

Router# show rib vrf all wait-install summary
Wed May 13 07:32:50.703 EDT

Sync Markers summary for client 'bgp 100-default upd-v4' (ID 46) on node0_0_CPU0

  Sync markers in-progress:        0
      In redist queue:             0
      Waiting for ACK:             0
      In notify queue:             0

  High watermark in-progress:     2

  Number of requests dropped:
      Stuck for too long:          0
      DB size limit exceeded:      0
  Requests forcefully marked as Ack: 0

Global Sync-Marker Timing Statistics

  Number of ACKs:                 3

  Shortest ACK response time:    1 ms [May 13 07:27:40.398]
    Object [Type: SYNC MARKER, client_id = 46, table_id = 0xe0000011, proto_id = 3, version = 7]

  Longest ACK response time:     104 ms [May 13 07:27:40.395]
    Object [Type: SYNC MARKER, client_id = 46, table_id = 0xe0000011, proto_id = 3, version = 5]

  Average ACK response time:     23 ms [May 13 07:27:40.395 - Now]
  Average install to FIB packing transition time: 11 ms [May 13 07:27:40.395 - Now]
  Average FIB packing to ACK response transition time: 12 ms [May 13 07:27:40.395 - Now]

  Number of NACKs:                0
  Number of aborted operations:   0

The RIB synchronization process is progressing correctly for all VRFs with the BGP route advertisement synchronization feature by checking the summary of sync markers.

4.

Verify that the BGP route advertisement synchronization feature is enabled on the specific address-family.

Example:



Router# show bgp ipv4 unicast process detail
!
....
Address family: IPv4 Unicast
 AS based ECMP Download Delay not configured
 OOR Flag 0 OOR Threshold 0
 Prefix Download Delay 0
 Inbound Route Delay 0 msec
Dampening is not enabled
Client reflection is enabled in global config
Dynamic MED is Disabled
Dynamic MED interval : 10 minutes
Dynamic MED Timer : Not Running
Dynamic MED Periodic Timer : Not Running
Update wait-install enabled:
  ack request 0, ack rcvd 0, slow ack 0
  startup delay 0 secs

The BGP route advertisement synchronization feature is enabled.

BGP route advertisement synchronization is operational. Routes are advertised only after hardware programming is confirmed, improving convergence reliability and reducing transient traffic issues.