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Routing

BGP and OSPF integration for subscriber route advertisement.

Overview​

AthenaBNG integrates with FRRouting to advertise subscriber routes to upstream networks via BGP and OSPF.

BGP Integration​

Neighbor Establishment​

  1. BNG initiates TCP connection to neighbor IP on port 179
  2. BGP OPEN message exchange
  3. Neighbor relationship established
  4. Route updates begin

Subscriber Route Advertisement​

When announce_subscriber_routes is enabled:

  1. Subscriber session established (PPPoE or DHCP)
  2. Subscriber IP assigned (e.g., 203.0.113.10)
  3. Host route created in kernel (/32 for PPPoE, /32 for DHCP)
  4. FRR picks up route via redistribute connected
  5. Route advertised to BGP neighbors
  6. Upstream network can reach subscriber directly

Route Withdrawal​

When subscriber disconnects:

  1. Session terminated
  2. Host route removed from kernel
  3. FRR withdraws route from BGP
  4. BGP neighbors receive withdrawal
  5. Route no longer reachable

OSPF Integration​

OSPF can be used for internal routing within the ISP network.

Configuration​

routing:
  bgp:
    enabled: true
    asn: 64512
    neighbors:
      - address: "10.255.0.254"
        remote_as: 64500
    announce_subscriber_routes: true
  ospf:
    enabled: false

Monitoring​

View BGP Summary​

abng> show bgp summary

View Routes​

abng> show routes

Check FRRouting Status​

sudo systemctl status frr
sudo vtysh -c "show bgp summary"

Troubleshooting​

BGP Neighbor Not Establishing​

  1. Check BGP is enabled: show configuration | match bgp
  2. Check neighbor is reachable: ping 10.255.0.254
  3. Check firewall allows TCP 179
  4. Check FRR is running: sudo systemctl status frr
  5. Check FRR logs: sudo vtysh -c "show bgp neighbors"

Subscriber Routes Not Advertised​

  1. Check route advertisement is enabled: show configuration | match announce_subscriber_routes
  2. Check subscriber route exists: show routes | match 203.0.113
  3. Check FRR is advertising: sudo vtysh -c "show bgp ipv4 unicast"
  4. Check neighbor is receiving: Check upstream router's BGP table

BGP Session Flapping​

  1. Check network stability: ping -c 100 10.255.0.254
  2. Check for configuration changes
  3. Check FRR logs: sudo journalctl -u frr -f
  4. Check for resource exhaustion: free -h, df -h

Best Practices​

  1. ASN — Use private ASN range (64512-65534 or 4200000000+)
  2. Router ID — Use loopback IP (system.router_id)
  3. Neighbors — Configure redundant neighbors for resilience
  4. Route Advertisement — Enable for subscriber reachability
  5. Monitoring — Monitor BGP session state and route count
  6. Testing — Test with traceroute from upstream
  7. Documentation — Document ASN and neighbor relationships

Next Steps​