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CloudEdge SAM: OCI Ubuntu image firewall bootstrap

Experimental (CloudEdge SAM). This is host bootstrap / provider-image behavior, not a routerd dataplane concern. It applies to OCI Canonical Ubuntu images used as SAM routers.

Symptom​

On OCI, the Canonical Ubuntu 24.04 image boots with iptables-nft filter rules that reject inbound traffic except SSH/ICMP and reject all FORWARD traffic. With these defaults a SAM router will:

  • receive no WireGuard handshake even though the OCI security list allows UDP/51820 and the VNIC has skipSourceDestCheck=true — the host firewall drops the inbound WireGuard packets before they reach the wg-hybrid listener;
  • not forward captured/overlay traffic — the default FORWARD reject blocks the SAM delivery path between the VNIC interface and wg-hybrid.

This is independent of the cloud security list / VNIC source-dest-check, which operate at the fabric layer; the guest OS firewall is a separate layer that must also permit the SAM paths.

Required allowances (guest OS)​

On each OCI SAM router, ensure the host firewall permits:

  • inbound UDP/51820 to the wg-hybrid WireGuard listener;
  • FORWARD between the OCI VNIC interface (e.g. ens3) and wg-hybrid in both directions.

Express these declaratively in the router config as part of host bootstrap (the same way other "router prerequisites" are declared so a clean host proves them), rather than relying on ad-hoc iptables rules that do not survive a rebuild.

Diagnosing it​

routerctl doctor hybrid surfaces guest-firewall reject-all FORWARD/INPUT patterns that would block the WireGuard / SAM paths, so a missing allowance is reported rather than appearing as a silent "no handshake". Run it on the OCI router after deploy:

routerctl doctor hybrid

If the WireGuard endpoint shows no handshake while the peer is sending keepalives, check the guest firewall first (this how-to), then the OCI security list, then the VNIC source-dest-check.

  • Selective Address Mobility
  • OCI Ubuntu images differ from AWS/Azure images in their default iptables-nft posture; AWS/Azure SAM smokes did not hit this because their images do not reject-all FORWARD by default.