Unable to create 2 firecracker VMs on separate networks

Question

I'm trying to SSH into 2 different firecracker VMs on the same host. I am creating the configuration dynamically as seen below. Both VMs should be fully isolated on their own network. I have 2 IPs allocated (1 for TUN and 1 for the VM).

I can SSH into VM1, but not VM2. Is my IP addressing logic incorrect? How can I properly understanding this.

#!/bin/bash

generate_config() {
  local machine_number="$1"
  local fc_ip="$2"
  local tap_ip="$3"
  local fc_mac="$4"
  local tap_dev="tap_${machine_number}"
  local mask_long="255.255.255.252"
  local mask_short="/30"

  ip link del "$tap_dev" 2> /dev/null || true
  ip tuntap add dev "$tap_dev" mode tap
  sysctl -w net.ipv4.conf.${tap_dev}.proxy_arp=1 > /dev/null
  sysctl -w net.ipv6.conf.${tap_dev}.disable_ipv6=1 > /dev/null
  ip addr add "${tap_ip}${mask_short}" dev "$tap_dev"
  ip link set dev "$tap_dev" up

  local kernel_boot_args="ro console=ttyS0 noapic reboot=k panic=1 pci=off nomodules random.trust_cpu=on"
  kernel_boot_args="${kernel_boot_args} ip=${fc_ip}::${tap_ip}:${mask_long}::eth0:off"

  cat > "firecracker_config_${machine_number}.json" << EOF
{
  "boot-source": {
    "kernel_image_path": "/root/setup/kernel",
    "boot_args": "${kernel_boot_args}"
  },
  "drives": [
    {
      "drive_id": "rootfs",
      "path_on_host": "/firecracker/filesystems/rootfs.ext4",
      "is_root_device": true,
      "is_read_only": false
    }
  ],
  "network-interfaces": [
    {
      "iface_id": "eth0",
      "guest_mac": "${fc_mac}",
      "host_dev_name": "${tap_dev}"
    }
  ]
}
EOF
}

# Generate configurations for two VMs
generate_config 1 "169.254.0.21" "169.254.0.22" "02:FC:00:00:00:05"
generate_config 2 "170.254.0.21" "170.254.0.22" "03:FC:00:00:00:05"

Answer 1

there is a dev tool that handles this problematic for you, https://github.com/cubewave/cubewave Maybe you could use that to bypass your own network configuration