Multiple VMs Might Break Network Connections

[iwinux]

OS / App Versions

• macOS 13.5 (x86-64)
• QEMU 7.2.1
• socket_vmnet 1.1.2 built from source

Problem

The network of currently started QEMU VM stops working (symptom: ping 1.1.1.1 times out) when another VM (with unique MAC address) boots up but DOES NOT initiate any DHCP request.

However, after the second VM finishes its DHCP request, the network on first VM resumes to normal.

Steps to Reproduce

1. start socket_vmnet

```bash sudo env DEBUG=true /usr/local/bin/socket_vmnet \ --socket-group=admin \ --vmnet-mode=shared \ --vmnet-gateway=10.233.2.1 \ --vmnet-dhcp-end=10.233.2.250 \ --vmnet-mask=255.255.255.0 \ /run/vmnet.sock ```

2. start VM `vmnet-test-01`

```bash # Alpine Live ISOs available at https://www.alpinelinux.org/downloads/ # The "Virtual" ones are smallest /usr/local/bin/socket_vmnet_client \ /run/vmnet.sock \ qemu-system-x86_64 \ -name "vmnet-test-01" \ -machine type=q35,accel=hvf \ -cpu host \ -smp cpus=1,sockets=1,cores=1,threads=1 \ -m 1024 \ -cdrom "$HOME/Downloads/alpine-virt-3.18.2-x86_64.iso" \ -netdev socket,id=net0,fd=3 \ -device "virtio-net-pci,netdev=net0,mac=de:ad:be:ef:00:01" \ -object rng-random,filename=/dev/urandom,id=rng0 \ -device virtio-rng-pci,rng=rng0 \ -device virtio-gpu-pci \ -nographic ```

3. acquire IP via DHCP for vmnet-test-01

```bash # login with user "root" cat > /etc/network/interfaces <<-END auto lo iface lo inet loopback auto eth0 iface eth0 inet dhcp END rc-service networking start # it pings successfully ping -c 5 -w 1 1.1.1.1 ```

4. start VM `vmnet-test-02`

```bash /usr/local/bin/socket_vmnet_client \ /run/vmnet.sock \ qemu-system-x86_64 \ -name "vmnet-test-02" \ -machine type=q35,accel=hvf \ -cpu host \ -smp cpus=1,sockets=1,cores=1,threads=1 \ -m 1024 \ -cdrom "$HOME/Downloads/alpine-virt-3.18.2-x86_64.iso" \ -netdev socket,id=net0,fd=3 \ -device "virtio-net-pci,netdev=net0,mac=de:ad:be:ef:00:02" \ -object rng-random,filename=/dev/urandom,id=rng0 \ -device virtio-rng-pci,rng=rng0 \ -device virtio-gpu-pci \ -nographic ```

5. after 1-2 minutes, network on vmnet-test-01 stops working

```bash # timeout ping -c 5 -w 1 1.1.1.1 # DHCP cannot renew lease rc-service networking restart ```

6. repeat step 3 for vmnet-test-02

```bash # login with user "root" cat > /etc/network/interfaces <<-END auto lo iface lo inet loopback auto eth0 iface eth0 inet dhcp END rc-service networking start # it pings successfully ping -c 5 -w 1 1.1.1.1 ```

7. surprisingly, now networks on both VMs resume to normal

Debug Log

https://gist.github.com/iwinux/305a9bea6b77c5c44494bb1883354f72

[nirs]

@iwinux can you reproduce this with lima >= 1.0.0?

Please test with current master, we have better logs now (see /var/log/socket_vmnet/stderr).

[nirs]

@iwinux can you reproduce this with lima >= 1.0.0?

I see you don't use lima, so it is not relevant.

[iwinux]

@nirs Cool, just noticed a lot of new commits since September. Will try with latest master version later.