debian instance not accessible when multiple network interfaces present

I created an instance with a Debian 12 cloud-init image with 3 network interfaces. When it came up, I was not able to access it via its external IP.

This is what it looks like from the CLI.

$ oxide instance view --instance cr0 --project router-testing
success
Instance {
    description: "Customer router zero",
    hostname: "cr0",
    id: dc0a52a1-db1c-4717-b3ac-28c7b106cad2,
    memory: ByteCount(
        8589934592,
    ),
    name: Name(
        "cr0",
    ),
    ncpus: InstanceCpuCount(
        4,
    ),
    project_id: 4d4a8023-a8c0-4c13-96b5-71cd04bd4402,
    run_state: Running,
    time_created: 2024-01-18T02:08:16.004264Z,
    time_modified: 2024-01-18T02:08:16.004264Z,
    time_run_state_updated: 2024-01-18T02:08:50.834602Z,
}

$ oxide instance nic list --instance cr0 --project router-testing
InstanceNetworkInterface {
    description: "",
    id: 0ce1343a-a174-4d68-8853-982f0b047024,
    instance_id: dc0a52a1-db1c-4717-b3ac-28c7b106cad2,
    ip: 172.30.0.9,
    mac: MacAddr(
        "A8:40:25:FD:F3:63",
    ),
    name: Name(
        "mgmt",
    ),
    primary: true,
    subnet_id: 9a1864b4-440b-428d-9e9e-0b949d7d1fe7,
    time_created: 2024-01-18T02:08:16.214846Z,
    time_modified: 2024-01-18T02:08:16.214846Z,
    vpc_id: f1db67cd-b1fd-49ef-8401-4c6691151e21,
}
InstanceNetworkInterface {
    description: "",
    id: f5b2572c-a7ce-4d45-9dff-d36bc528e841,
    instance_id: dc0a52a1-db1c-4717-b3ac-28c7b106cad2,
    ip: 10.0.0.10,
    mac: MacAddr(
        "A8:40:25:FC:75:BE",
    ),
    name: Name(
        "sw0",
    ),
    primary: false,
    subnet_id: b0703d91-4097-49b1-a7b6-197be5b108ca,
    time_created: 2024-01-18T02:08:16.433674Z,
    time_modified: 2024-01-18T02:08:16.433674Z,
    vpc_id: f1db67cd-b1fd-49ef-8401-4c6691151e21,
}
InstanceNetworkInterface {
    description: "",
    id: 1a51f3d0-8911-4ab0-9dbd-b0b8c6e0ca65,
    instance_id: dc0a52a1-db1c-4717-b3ac-28c7b106cad2,
    ip: 10.0.1.10,
    mac: MacAddr(
        "A8:40:25:F8:74:4B",
    ),
    name: Name(
        "sw1",
    ),
    primary: false,
    subnet_id: d4bc0098-ab25-4315-911e-46984d40558c,
    time_created: 2024-01-18T02:08:16.645434Z,
    time_modified: 2024-01-18T02:08:16.645434Z,
    vpc_id: f1db67cd-b1fd-49ef-8401-4c6691151e21,
}

From the instance console output, it looks like the default route is being assigned the wrong gateway.

[    7.072788] cloud-init[424]: ci-info: ++++++++++++++++++++++++++++Route IPv4 info+++++++++++++++++++++++++++++
[    7.076163] cloud-init[424]: ci-info: +-------+-------------+----------+-----------------+-----------+-------+
[    7.079531] cloud-init[424]: ci-info: | Route | Destination | Gateway  |     Genmask     | Interface | Flags |
[    7.082890] cloud-init[424]: ci-info: +-------+-------------+----------+-----------------+-----------+-------+
[    7.086241] cloud-init[424]: ci-info: |   0   |   0.0.0.0   | 10.0.1.1 |     0.0.0.0     |   enp0s8  |   UG  |
[    7.089635] cloud-init[424]: ci-info: |   1   |   1.1.1.1   | 10.0.1.1 | 255.255.255.255 |   enp0s8  |  UGH  |
[    7.092972] cloud-init[424]: ci-info: |   2   |   8.8.8.8   | 10.0.1.1 | 255.255.255.255 |   enp0s8  |  UGH  |
[    7.096323] cloud-init[424]: ci-info: |   3   |   10.0.1.1  | 0.0.0.0  | 255.255.255.255 |   enp0s8  |   UH  |
[    7.099669] cloud-init[424]: ci-info: +-------+-------------+----------+-----------------+-----------+-------+

It also looks like some address assignments are missing.

[    7.027556] cloud-init[424]: ci-info: +++++++++++++++++++++++++++++++++++++++++Net device info+++++++++++++++++++++++++++++++++++++++++
[    7.031646] cloud-init[424]: ci-info: +---------+-------+------------------------------+-----------------+--------+-------------------+
[    7.035839] cloud-init[424]: ci-info: |  Device |   Up  |           Address            |       Mask      | Scope  |     Hw-Address    |
[    7.039945] cloud-init[424]: ci-info: +---------+-------+------------------------------+-----------------+--------+-------------------+
[    7.044096] cloud-init[424]: ci-info: | enp0s10 | False |              .               |        .        |   .    | a8:40:25:fc:75:be |
[    7.048215] cloud-init[424]: ci-info: |  enp0s8 |  True |          10.0.1.10           | 255.255.255.255 | global | a8:40:25:f8:74:4b |
[    7.052324] cloud-init[424]: ci-info: |  enp0s8 |  True | fe80::aa40:25ff:fef8:744b/64 |        .        |  link  | a8:40:25:f8:74:4b |
[    7.056441] cloud-init[424]: ci-info: |  enp0s9 | False |              .               |        .        |   .    | a8:40:25:fd:f3:63 |
[    7.060527] cloud-init[424]: ci-info: |    lo   |  True |          127.0.0.1           |    255.0.0.0    |  host  |         .         |
[    7.064617] cloud-init[424]: ci-info: |    lo   |  True |           ::1/128            |        .        |  host  |         .         |
[    7.068703] cloud-init[424]: ci-info: +---------+-------+------------------------------+-----------------+--------+-------------------+

Reproduce a Debian 12 cloud-init instance with three network interfaces, using the oxide instance view and oxide instance nic list CLI entry points and the instance console output. Inspect why only one interface receives an address and why the default route uses the wrong gateway; done means external-IP access works with correct interface addresses and routing.