Case Studies and Implementation Examples¶

This section covers practical implementation scenarios for BGP in Red Hat OpenStack Platform.

Scenario 1: Control Plane High Availability¶

BGP enables highly available OpenStack API endpoints without traditional L2 spanning across sites.

Technical implementation:

Controllers deployed across multiple racks in separate L3 segments
Each rack’s Top-of-Rack (ToR) switch acts as a BGP peer
Control plane services use a VIP advertised via BGP

FRR configuration example:

# FRR configuration on OpenStack Controller
router bgp 64999
  bgp router-id 172.30.1.1
  neighbor 172.30.1.254 remote-as 65000
  address-family ipv4 unicast
    network 192.1.1.1/32
  exit-address-family

OVN BGP agent monitors control plane events
Pacemaker influences BGP route advertisements based on controller health
Fast convergence enables rapid failover

Scenario 2: Multi-Cloud Connectivity¶

BGP enables secure connectivity between multiple OpenStack clouds and external networks.

Technical implementation:

Each OpenStack cloud uses a unique ASN
Border nodes run FRR with eBGP peering to external routers

FRR configuration example:

# FRR configuration on border node
router bgp 64999
  bgp router-id 10.0.0.1
  neighbor 203.0.113.1 remote-as 65001  # External peer
  address-family ipv4 unicast
    network 172.16.0.0/16  # Tenant network range
    redistribute connected
  exit-address-family

IP rules configured by OVN BGP agent:

# IP rules example
$ ip rule
     from all lookup local
  from all lookup [l3mdev-table]
 from all to 172.16.0.0/16 lookup br-ex  # tenant networks
 from all lookup main
 from all lookup default

Scenario 3: ECMP Load Balancing and Redundancy¶

FRR implements Equal-Cost Multi-Path (ECMP) routing for load balancing and redundancy.

Technical implementation:

ECMP configuration in FRR:

# ECMP configuration
router bgp 64999
  maximum-paths 8
  maximum-paths ibgp 8

BFD for fast failure detection:

# BFD configuration
router bgp 64999
  neighbor 192.0.2.1 bfd
  neighbor 192.0.2.2 bfd

Traffic auto-rerouted to available paths during failures

OVN BGP agent configuration for traffic flow:

# BGP traffic redirection components:
- Dummy interface (bgp-nic) added to VRF (bgp_vrf)
- Routes added to OVS provider bridge table
- ARP/NDP entries configured for OVN router gateway ports
- OVS flows for traffic redirection

Scenario 4: Dynamic Route Advertisement¶

BGP simplifies scaling by dynamically advertising routes as new resources are provisioned.

Implementation workflow:

New VM with IP 172.16.5.10 created on Compute node
OVN BGP agent detects VM in southbound database
Agent adds IP to dummy interface: `$ ip addr add 172.16.5.10/32 dev bgp-nic`
FRR’s Zebra daemon detects IP and advertises via BGP
Agent configures traffic redirection: `$ ovs-ofctl add-flow br-ex "priority=900,ip,in_port=patch-provnet-1,actions=mod_dl_dst:<bridge_mac>,NORMAL"`
External BGP peers receive route and can reach VM

For floating IPs, similar automation occurs when they’re associated with instances, eliminating manual route configuration as the environment scales.

Scenario 5: Distributed L2 Provider VLANs¶

BGP allows distributing L2 provider VLANs and floating IP subnets across L3 boundaries.

Technical implementation:

Provider VLANs distributed across racks without spanning VLANs (for non-overlapping CIDRs)
Configuration allows separation of provider networks across physical boundaries
Traffic routed between segments using BGP-advertised routes instead of traditional L2 connectivity
Simplified network design with reduced broadcast domains

Scenario 6: Tenant Network Exposure¶

OpenStack can optionally expose tenant networks via BGP using a special configuration flag.

Technical implementation:

Set the expose_tenant_networks flag to True in OVN BGP agent configuration:
```
[DEFAULT]
expose_tenant_networks = True
```
With this setting, tenant network IPs are advertised just like provider networks
This feature requires non-overlapping CIDRs across tenants
Tenant VMs become directly reachable from external networks without floating IPs