When the mcp-br0 bridge exists, the agent runs unikernels on it instead
of QEMU user-mode networking: each VM gets a TAP device on the bridge
and a static 10.99.0.0/24 IP (baked into the Nanos image via ops
RunConfig). With the host firewall dropping off-bridge VM traffic and no
NAT, a VM can reach only the gateway -- making mc-proxy mediation
mandatory by topology rather than convention.
- runtime/qemu.go: bridge mode (createTAP/destroyTAP, IP allocator,
deterministic MAC, static-IP ops config, VMAddr for proxy backends).
- agent auto-enables bridge mode when /sys/class/net/mcp-br0 exists.
Verified on straylight: uktest unikernel boots on mcp-br0 at 10.99.0.2,
serves via the gateway, TAP enslaved to the bridge; bridge has no uplink
and off-bridge forwarding is dropped.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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