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

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BGP next hop trigger delay

Updated: February 28, 2026

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Overview

Explains how BGP next hop trigger delay batches next-hop change notifications to reduce CPU load and controls next-hop walk frequency using configurable batching intervals.

BGP next hop trigger delay is a BGP mechanism that

  • batches next-hop change notifications to reduce CPU load and avoid unnecessary next-hop walks

  • uses the Routing Information Base (RIB) classification of critical and noncritical events, and

  • applies a configurable minimum batching interval per address family to control next-hop walk frequency.

How BGP next hop trigger delay works

Summary

The key components involved in the process are:

  • Routing Information Base (RIB): Classifies change notifications as critical or noncritical.

  • Batching interval: A configured minimum delay that governs next-hop walk scheduling.

  • Address families: IPv4 and IPv6 unicast contexts where batching is applied.

  • Next-hop walk scheduler: Executes deferred, batched walks based on classification and interval.

BGP next hop trigger delay improves stability by batching next-hop change notifications, reducing CPU load, and controlling how often next-hop walks run per address family.

Workflow

These stages describe how BGP next hop trigger delay works.

  1. Classification: The RIB labels each next-hop change notification as critical or noncritical.
  2. Interval application: The router applies the configured batching interval to defer next-hop walks for each address family.
  3. Batch formation: Deferred notifications accumulate into batches for efficient processing.
  4. Interleaved execution: Batched walks are interleaved across address families to prioritize work and avoid contention.
  5. Stabilization: Controlled, batched processing reduces churn, improves stability, and supports faster convergence.

Result

Next-hop change notifications are batched and interleaved across address families, lowering CPU utilization and enhancing routing stability and convergence.

Guidelines for BGP next hop trigger delay

Recommendation: Use a nonzero critical next hop trigger delay

  • Avoid a critical delay set to 0 in scaled environments or where next-hop changes are frequent.

  • A zero delay causes high CPU utilization due to repeated next-hop walks, prevents batching, and increases wait times for address families with nonzero delays, risking traffic blackholing.

  • In IPv4, a zero critical delay can slow VPNv4 convergence because IPv4 next-hop updates take precedence.

Effects of zero critical delay

Provide a concise, actionable summary of the operational impacts of setting the BGP next hop trigger delay critical value to 0.

  • In scaled deployments or where next-hop changes are frequent, a zero critical delay causes high CPU utilization because each change notification triggers a next-hop walk for address families configured with the nexthop trigger-delay critical 0 command.

  • Next-hop change notifications are not batched, which prevents interleaving of next-hop walks in address families with a nonzero delay because those families wait until the zero-delay walks complete.

  • Address families with nonzero critical delay values may experience extended wait times before the next-hop walk starts, which can lead to potential traffic blackholing.

  • In IPv4, setting the critical delay to 0 can slow VPNv4 convergence because:

    • IPv4 address families are walked as many times as the number of critical alerts raised to BGP.

    • IPv4 next-hop updates for IPv4 prefixes take precedence over VPNv4 prefixes.

Default next hop trigger delay values

Table 1. Default values for next hop trigger delay

Address families

Value

Notes

Default critical delay

Standard address families

3,000 ms

Default critical delay

VPNv4, VPNv6

50 ms

Starting in Cisco IOS XR Release 7.10.1, the default critical delay in VPNv4 changed from 0 ms to 50 ms. With this change, all address families have a default nonzero critical delay value.

Default noncritical delay

All address families

10,000 ms

Use the show bgp all all nexthops command to view the critical delay values per address family.

Configure BGP next hop trigger delay

Batch next-hop change notifications to reduce CPU load and avoid unnecessary next-hop walks.

The RIB classifies change notifications as critical and noncritical. A minimum batching interval controls how often next-hop walks run per address family.

Before you begin

Verify the desired delay values for critical and noncritical events per address family.

Procedure

1.

Enter the BGP configuration mode and specify the autonomous system number.

Example:

Router# configure
Router(config)# router bgp 120
2.

Specify the address family, IPv4 or IPv6, in unicast mode.

Example:

Router(config-bgp)# address-family ipv4 unicast
3.

Configure nexthop trigger-delay critical delay or nexthop trigger-delay noncritical delay for batching intervals.

Example:

Router(config-bgp-af)# nexthop trigger-delay critical 15000
Router(config-bgp-af)# commit