Network Isolation

NICo enforces tenant network isolation across three independent fabrics. Each fabric uses a different mechanism, is configured through a different operator API, and is verified separately. This page summarises the model so an operator can choose the right guide; it is not a replacement for the per-fabric configuration guides linked below.

Who configures what, and how

Network operations split across two roles. The per-fabric guides tag every operation with its role and interface using the model below; read this once, then use the operations matrix in each guide.

Operator (site administrator)

• Day-0 site setup is TOML in the API server configuration. After Day 0, TOML changes are rare.
• For Day-1+ operations, prefer the REST API, or nicocli (its CLI wrapper).
• Use nico-admin-cli (which speaks the gRPC API directly) only for operations the REST API does not expose — for example, NMX-C endpoint registration, the NVLink GPU-mapping populate step, or break-glass fabric cleanup.

Tenant

• Never edits TOML.
• Uses the REST API or nicocli exclusively.
• If neither exposes a required operation, that is a gap: file a bug against the REST API / nicocli rather than reaching for nico-admin-cli.

REST paths in the matrices are shown against the /v2/org/{org}/nico/... placeholder; nicocli commands follow the nicocli <resource> <verb> form. See the REST API Reference tab and the nicocli Reference for exact request bodies and flags.

Ethernet

Operations

See Who configures what, and how for the role and interface model.

A tenant’s instance reaches a VPC by drawing addresses from one of the VpcPrefixes attached to that VPC. NICo carves a /31 link-net per interface from the prefix — one address to the instance, one to the DPU’s SVI in the VPC’s VRF. An instance may participate in several VPCs at once by having interfaces drawing from prefixes in different VPCs. On the DPU of the managed host backing the instance, each related VPC materialises as a Linux VRF; every host interface drawing from a prefix in that VPC lives in that VRF. The tenant overlay is a pure type-5 EVPN (IP-prefix) overlay — NICo does not stretch any tenant L2 segment across the fabric.

Ethernet isolation has three independent layers:

• Routing isolation (VPC / VRF). VRFs are isolated by default. A route advertised in one VPC does not appear in another VPC’s VRF. Cross-VPC reachability is opt-in via VPC peering or controlled route leaking on the VPC’s routing profile.
• Default isolation (admin overlay). A managed host never carries tenant traffic unless a tenant configuration places it in a VPC. Between tenants, during provisioning / termination, or when its configuration is unknown, the DPU is held on the admin overlay (fail-closed).
• L3 / L4 filtering (Network Security Groups). Stateful or stateless rule-based filtering within or across VPCs, attached at VPC or instance scope.

The Ethernet configuration model is documented in the VPC manuals; this overview does not duplicate them:

• VPC Network Virtualization — the full VXLAN / EVPN, VRF, BGP, routing-profile, and DPU-config reference, including Default Isolation: The Admin Overlay
• VPC Routing Profiles — route-target imports / exports and controlled route leaking
• VPC Peering — opt-in cross-VPC reachability
• Network Security Groups — L3 / L4 rule filtering and site-wide operator overrides
• Flat VPCs and Zero-DPU Hosts — the operator-managed data plane for hosts without a NICo-managed DPU

InfiniBand

Each tenant InfiniBand partition maps to a UFM P_Key. Membership is enforced by the subnet manager at the fabric level: hosts that are not members of a P_Key cannot exchange traffic with other members of that P_Key, regardless of physical connectivity. NICo reconciles desired partition membership against UFM via the IbFabricMonitor background task and surfaces the synchronisation status to operators and to tenants.

See Configuring InfiniBand Partitions for the operator configuration guide, and the InfiniBand Setup Runbook for the prerequisite UFM / OpenSM hardening.

NVLink

NVLink logical partitions group GPUs across hosts into a single isolated NVLink domain. NICo drives partition lifecycle against the NMX-M REST API and the NMX-C gRPC API and reconciles desired partitions periodically. Each tenant instance that requests NVLink connectivity is placed into the partition corresponding to its allocation; a host whose GPUs are not in a partition cannot reach any other host’s GPUs over NVLink.

See NVLink Partitioning for the operator configuration guide.

Cross-cutting behaviour

The following invariants apply to every fabric.

• Per-fabric synchronisation status. Each instance’s InstanceStatus exposes a per-fabric configs_synced field that is true only when the observed fabric state matches the desired configuration. The aggregate configs_synced field is the logical AND of all per-fabric fields and gates the instance’s Ready state.
• Provisioning blocks on isolation convergence. During initial provisioning, the instance state machine waits until every requested fabric has applied the desired configuration before the instance is marked Ready. Tenants observe this as the Configuring tenant state, and the machine remains in WaitingForNetworkConfig until the DPU reports back.
• Termination blocks on isolation convergence. During termination, the state machine waits until every fabric reports that the host has been removed from all tenant partitions before the instance is reported as deleted. This guarantees a terminated instance cannot continue to exchange traffic on any fabric.
• Force-delete still tears down fabric state. Force-deleting a managed host explicitly detaches it from every fabric through the same external APIs the normal lifecycle uses, so external fabric managers do not retain stale tenant references.
• External fabric reachability is monitored. Each external fabric service (UFM, NMX-M, NMX-C) is monitored from NICo with request-success and latency metrics so that fabric-side outages can be distinguished from NICo-side configuration errors.

For the architectural rationale and the patterns shared across all three fabrics, see Networking Integrations.

For the Day 0 IP, DHCP, DNS, and admin-network configuration that every isolation guarantee on this page rests on, see Day 0 IP and Network Configuration.