Can't access vzNAT IP address without sudo on macOS

[thomasjm]

Description

I've been trying to track down a weird problem where I start a Lima VM with the "Docker" template, and start a Docker container that runs a web server, and try to connect to it using the vzNAT IP address assigned to the VM:

limactl start --name test1 template:docker --network=vzNAT --vm-type=vz
export DOCKER_HOST=unix://$HOME/.lima/test1/sock/docker.sock
docker run -d -p 8080:80 nginx:alpine
VZNAT_IP=$(limactl shell test1 ip -j route get 8.8.8.8 | jq -r '.[0].prefsrc')

At this point, doing curl $VZNAT_IP:8080 works and I see the Nginx welcome page.

However, I've created a small C program which tries to create a socket and connect to the same hostname/port. But when I try to run it, I get an error:

> gcc test.c && ./a.out "$VZNAT_IP" 8080
host: 192.168.64.19
port: 8080
Family: 2, Protocol: 6
Socket created: 3
connect() failed: No route to host

But here's the crazy thing: if I use sudo, it works!

sudo ./a.out "$VZNAT_IP" 8080
host: 192.168.64.19
port: 8080
Family: 2, Protocol: 6
Socket created: 3
Connected successfully!

I'm finding this really baffling. Why the discrepancy between curl and my C program? I'd like to run dtruss on curl but it doesn't work without disabling System Integrity Protection. Even weirder, I've tried testing this with a retry every 1 second for a long time, and occasionally I've seen it suddenly manage to connect after a while?

I'm using Lima 2.0.1. I also tried Lima 1.1.1 since I remember this working better in the past, and got the same result. The main thing I can think of that has changed recently is that I upgraded to macOS Tahoe? Any help figuring this out would be much appreciated!

[nirs]

@thomasjm curl results looks correct, the instance should be accessible from the host.

The small C program gets a linked list of addrinfo structs. You always access the first item in the list, and you don't print the value of res->ai_addrlen and res->ai_addr. Maybe you get different results when running as user or as root?

But it is not clear why you wrote that program. What is the issue you are trying to solve?

[thomasjm]

But it is not clear why you wrote that program. What is the issue you are trying to solve?

I'm working on an app which needs to start services on Lima VMs and connect to them. It's the connection part that's been failing for me so I wrote the C program as a minimal way to debug the socket connection.

Maybe you get different results when running as user or as root?

Good point, I just extended the C program to print all the addrinfo structs and those other fields. The results are identical between my user and root.

Here's another one: doing telnet "$VZNAT_IP" 8080 fails (with No route to host). But adding a sudo makes it connect successfully!

[thomasjm]

Uh oh, I think it may be this: https://dev.iachieved.it/iachievedit/macos-sequoia-no-route-to-host/

I think macOS is treating the vzNAT IP address as a "local network connection" and refusing access for untrusted binaries. That's why it works with the system curl, but not with the telnet I installed via Nix, or my own C binary.

This is unfortunate because I don't like using the localhost port forwarding due to various issues: #3604, #2122, #2536.

Is there perhaps any other way to make a network connection to the Lima VM?

[AkihiroSuda]

The issue doesn't seem to happen for me

• macOS 26.1
• No relevant configuration in System Settings → Privacy & Security → Local Network
• Firewall is enabled, with Block all incoming connections and Enable stealth mode

[thomasjm]

The issue can even be triggered by running in a local Tmux session. If I run in a terminal with Tmux (installed via Nix) that's enough to cause the failure. I'm not sure what happens if you have a Tmux installed via other means like homebrew. Does that allow you to repro @AkihiroSuda ?

Doing it in a normal Iterm2 terminal succeeds.

[thomasjm]

Hello, can anyone else repro this? I'd like to confirm I'm not crazy :)

[nirs]

@thomasjm Do you use the builtin Terminal.app or other terminal like iTerm? The builtin Terminal.app is allowed to access local network but another terminal application may need approval. You can approve in System Settings -> Privacy & Security -> Local Network.

[norio-nomura]

Hello, can anyone else repro this? I'd like to confirm I'm not crazy :)

I also encountered the inability to access the VM via vzNAT (with No route to host) in #4175.

[nirs]

@norio-nomura So this happens in the CI? can you reproduce it locally? Which terminal application are you using?