Full Mesh Topology for High Availability¶

Status¶

Accepted — the platform standardizes a full mesh Layer-3 topology between core edge routers and firewalls to ensure deterministic routing and fault isolation.

Context¶

Earlier test environments used a hub-and-spoke design between CSR routers and pfSense/VyOS nodes.
This was simple but introduced clear single points of failure:

Hub failure affecting all spokes
Asymmetric routing during VPN cutovers
Complex troubleshooting when the “hub” was also running experiments

HybridOps.Studio’s networking layer now underpins:

Dual-ISP connectivity and IPsec DR tunnels (see ADR-0106)
Distributed monitoring agents and collectors (Prometheus, NetBox exporters)
Cross-site automation workflows (Nornir / Ansible against multiple “sites”)

A full mesh topology ensures each router maintains a direct path to all other peers, enabling redundant data planes even when individual links or nodes fail.

Decision¶

Adopt a full mesh L3 topology across all edge routers and firewalls in the WAN/edge layer:

Each router (CSR1000v, VyOS, pfSense) forms direct adjacencies with all other peers.
Transit uses dedicated VLANs over Proxmox bridges (for on-prem) and equivalent segments in EVE-NG (for simulated sites).
An optional overlay (e.g. VXLAN) provides a management reachability plane that is independent of the underlay.

Implementation Summary¶

Routing protocol
eBGP between all edge routers, no route reflectors (small node count).
Deterministic local-preference and MED policies for primary vs secondary paths.
Physical / virtual transport
Tagged VLANs on Proxmox bridges (e.g. vmbr2, vmbr3) for router-to-router transit.
Equivalent VLANs / links defined in EVE-NG topologies.
Overlay (optional)
VXLAN (e.g. 172.16.50.0/24) for management/control-plane reachability.
Used for automation access when underlay is impaired.
Resiliency testing
Simulated link failures and router reboots.
Target convergence time < 3 seconds for core prefixes.
Test artefacts stored in output/artifacts/networking/full-mesh-tests/.

Consequences¶

Positive¶

✅ Removes single-hub routing dependencies; multiple independent paths exist.
✅ Simplifies hybrid DR link migration and cloud cutover experiments.
✅ Mirrors typical enterprise designs where DC/edge devices are fully meshed at L3.
✅ Ensures parity between on-prem Proxmox topologies and EVE-NG simulations.

Negative¶

⚠ More interfaces, VLANs, and configuration blocks per device.
⚠ Slightly higher control-plane chatter (BGP sessions) — acceptable at current scale.
⚠ Requires disciplined IP addressing and documentation for transit networks.

Neutral¶

Topology can be collapsed back to hub-and-spoke for specific labs if needed.
Scaling beyond a small number of nodes may require introducing route reflectors or hierarchical designs (out of scope for this ADR).

References¶

Maintainer: HybridOps.Studio License: MIT-0 for code, CC-BY-4.0 for documentation unless otherwise stated.