FreeRADIUS AAA & BNG Dynamic Session Rebalancing
An architectural guide for ISP network engineers on scaling FreeRADIUS v3/v4 clusters, balancing PPPoE/IPoE subscriber sessions across redundant BNG routers, and enforcing zero-downtime CoA rate modifications.
1. High-Availability FreeRADIUS Clustering Architecture
Operating a carrier-grade ISP requires 99.999% availability for Authentication, Authorization, and Accounting (AAA). When a primary BNG or FreeRADIUS node experiences hardware fault, thousands of PPPoE tunnels attempt simultaneous re-authentication, causing RADIUS storm deadlocks unless distributed state caching is enforced.
In a Kashtrix-managed AAA deployment, incoming RADIUS Access-Requests and Accounting-Packets pass through an Anycast load balancer running `rlm_raw` and Redis session state storage. This isolates database writes from real-time authentication evaluation.
2. BNG Session Migration via RADIUS CoA & Disconnect-Messages
When balancing subscriber load between edge BNG routers (e.g., MikroTik CCR2216, Cisco ASR9000, or Juniper MX), the control plane transmits RFC 3576 RADIUS Disconnect (DM) or Change-of-Authorization (CoA) attributes:
Kashtrix Telecom Architecture Team
Verified AuthorLead AAA & Network Infrastructure Specialist
Specializes in carrier RADIUS cluster tuning, BNG session optimization, and high-throughput accounting database architecture.
[Verified Operator Case Study - Name Confidential]
Legacy billing software caused high dunning churn, database deadlocks during bill run peak hours, and lacked automated CGNAT subpoena log retrieval.
Deployed Kashtrix Unified OSS/BSS with integrated FreeRADIUS AAA clusters, automated WhatsApp invoice dunning, and 100k EPS Syslog CGNAT collector.
Measured Technical Outcomes
3. Frequently Asked Questions
How does RADIUS CoA (Change of Authorization) work during BNG session rebalancing?
RADIUS CoA packets (RFC 3576) are transmitted from the AAA server to the BNG to modify active subscriber bandwidth profiles or disconnect sessions without dropping subscriber physical link status.
What load-balancing algorithms should be used across active-active FreeRADIUS nodes?
Active-active AAA clusters utilize VRRP or IP Anycast combined with weight-based session hashing (Source-IP + Calling-Station-ID) to ensure accounting packets land on the same node holding active memory state.
How does AI detect abnormal AAA session flapping?
Kashtrix NOC AI monitors Access-Request retry frequencies and RADIUS Stop accounting logs. If flapping exceeds 5 reconnects per minute per ONT, the AI flags optical degradation or duplicate MAC credentials.