Networking

References:
internal/server/orchestrator/orchestrator.go (resolveNetworkConfig, needsIPAllocation, needsTapDevice), internal/server/orchestrator/network/{bridge.go,noop.go}, internal/setup/setup.go.

Volant supports three network modes via the plugin manifest (or per‑VM config override):

• bridged (default)
• vsock
• dhcp

The effective mode is resolved by resolveNetworkConfig(manifest, vmConfig). VM‑level config overrides the manifest.

What each mode means

• bridged:

  • Host creates a tap device and attaches it to the configured Linux bridge (vbr0 by default).
  • Orchestrator allocates an IP from the managed subnet and programs the VM kernel cmdline with ip/gateway/netmask.
  • needsTapDevice = true; needsIPAllocation = true.

• vsock:

  • No guest Ethernet; communication via vsock only (kestrel agent proxy).
  • No tap device and no host‑managed IP.
  • needsTapDevice = false; needsIPAllocation = false.

• dhcp:

  • VM gets IP via DHCP from inside the guest; host only provides a tap/bridge.
  • needsTapDevice = true; needsIPAllocation = false.

Host networking on Linux

• Bridge manager (internal/server/orchestrator/network/bridge.go) uses vishvananda/netlink to:
  • Ensure the bridge exists and is up
  • Create a tap interface with VNET_HDR and attach it to the bridge
  • Bring it up and hand the tap name to the runtime
• The bridge code is linux‑only (build‑tagged). On non‑Linux hosts, volantd falls back to NoopManager.

macOS and non‑Linux hosts

• No tap devices are created automatically. volantd logs a warning and uses NoopManager which returns a deterministic tap name (no system changes).
• If you want bridged networking on macOS, create and manage the tap/bridge manually and point your runtime to it.

Setup helper (Linux)

The CLI command volar setup (internal/cli/standard/setup.go) calls internal/setup/ to:

• Create bridge (default vbr0) and assign host IP (default 192.168.127.1/24)
• Enable IP forwarding and add MASQUERADE and FORWARD rules via iptables
• Optionally write a systemd unit for volantd with proper environment

You can run with --dry-run to print commands without applying them.

Kernel cmdline and IP

For bridged mode, the orchestrator computes:

• ip=<guest_ip>::<gateway>:<netmask>:<hostname>:eth0:off
• gateway = hostIP from config
• netmask derived from subnet mask (formatNetmask)

This is passed to the runtime; the guest should configure eth0 accordingly on boot.