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DUT gateway management (dut_gateway.py)

scripts/switch/dut_gateway.py updates the default gateway and DNS on all physical DUTs over parallel SSH immediately after a VLAN switch. It is called automatically by the labgrid-switch-abstraction library when switch-vlan changes the network mode — operators normally do not invoke it directly.

1. Why a separate gateway step?

When a DUT moves between VLANs its upstream router changes:

Mode VLAN Gateway DNS
Isolated (OpenWrt tests) 100–105 per DUT 192.168.<vlan>.254 (per-VLAN gateway) same
Mesh (LibreMesh tests) 200 192.168.200.254 (MESH_GATEWAY) 192.168.200.254

A simple VLAN change on the switch port is not enough: OpenWrt keeps the old default route in memory. dut_gateway.py pushes a shell script to each DUT that:

  1. Persists the new gateway and DNS in UCI (uci set network.lan.gateway, uci commit)
  2. Applies the route instantly with ip route replace default via <gw> (no reboot needed)
  3. Ensures a source IP in the gateway subnet exists on br-lan so the gateway can route replies back to the DUT

2. How it is called

The function update_dut_gateways(mode, ...) is called by switch_abstraction after every VLAN transition:

from switch.dut_gateway import update_dut_gateways

update_dut_gateways(
    mode="mesh",           # "mesh" or "isolated"
    config_path=Path("configs/dut-config.yaml"),
    settle_seconds=5,      # wait for VLAN propagation before SSH
)

The settle_seconds delay (default 5 s) absorbs the time for the managed switch to apply the VLAN change before SSH connections are attempted.

3. Shell script pushed to each DUT

For mesh mode (MESH_GATEWAY = 192.168.200.254):

uci delete network.lan.gateway 2>/dev/null; true
uci set network.lan.gateway='192.168.200.254'
uci set network.lan.dns='192.168.200.254'
uci commit network
ip route replace default via 192.168.200.254 dev br-lan src 10.13.200.11

For isolated mode (e.g. DUT on VLAN 100):

uci delete network.lan.gateway 2>/dev/null; true
uci set network.lan.gateway='192.168.100.254'
uci set network.lan.dns='192.168.100.254'
uci commit network
ip route replace default via 192.168.100.254 dev br-lan src 10.13.200.11

4. Parallel SSH execution

All DUTs are updated in parallel using subprocess with a 10-second SSH timeout. SSH options used:

-o StrictHostKeyChecking=no
-o UserKnownHostsFile=/dev/null
-o ConnectTimeout=10
-o LogLevel=ERROR

Each DUT is identified by its ssh_alias field from dut-config.yaml (e.g. dut-belkin-1). See SSH access to DUTs for how aliases are configured.

5. Troubleshooting

Symptom Likely cause Fix
SSH timeout on one DUT DUT still in isolated VLAN, SSH not reachable yet Increase settle_seconds or check switch VLAN assignment
Connection refused DUT powered off or sshd not running Power on DUT, check serial console
Gateway not applied after SSH succeeds Script ran but UCI/route failed SSH into DUT manually, check logread, re-run switch-vlan
All DUTs fail immediately dut-config.yaml not found or ssh_alias missing Verify configs/dut-config.yaml and DUT entries

See also