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Routing

BGP Communities

This feature enables configuration of BGP communities on a per-device, per-protocol (IPv4/IPv6), and per-VRF basis.

BGP communities settings

Problem Statement

During network discovery processes, full routing tables containing BGP routes is typically downloaded. This operation faces two challenges:

  1. Extremely large BGP tables can significantly prolong discovery
  2. Unnecessary route processing increases resource consumption

Solution 1: Global BGP Threshold

A global limit for BGP route downloads can be set in Discovery settings under Limit download BGP routes.

This solution presents an all-or-nothing approach, lacking flexibility and adaptability.

Solution 2: BGP Communities (Filter Lists)

BGP communities filters can be set for more precise control:

  1. Specify device by serial number
  2. Select protocol (IPv4/IPv6)
  3. Define VRF
  4. List BGP communities (or import them from file)

Routes matching these filters will be downloaded, while others are excluded.

How to add BGP community filter

Discovery Process Prioritization

graph TD
    A[Start Discovery] --> B{BGP Communities Configured?}
    B -->|Yes| C[Download filtered routes per community rules]
    C --> D[Complete Discovery]
    B -->|No| E{BGP Threshold Set?}
    E -->|Yes| F[Download routes if the number of routes available is less than the limit.]
    F --> D
    E -->|No| G[Download all BGP routes]
    G --> D

Key Behaviors

  1. Community Configuration Priority
    When present, BGP communities override thresholds. The system:

    • Downloads all routes matching community filters (on Cisco IOS-XR router, processing a large number of routes in the community may take some time)
    • Ignores threshold limits
    • Processes all specified VRFs

  2. Threshold Fallback
    Without community configuration:

    • Applies global threshold
    • Skips BGP download if route count exceeds threshold

  3. Empty Configuration
    Without either setting:

    • Downloads complete BGP table
    • Maximum resource consumption

Performance Considerations

Configuration Type Speed Resource Usage Precision
No filters/threshold Slowest Highest Full data
BGP Threshold Only Faster Moderate Partial
BGP Community Filters Fastest Lowest Targeted