Routing

BGP Communities

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

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.

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