Port Forwarding

Lima supports automatic port-forwarding of localhost ports from guest to host.

Port forwarding types

Lima supports two port forwarders: SSH and GRPC.

The default port forwarder is shown in the following table.

The default was once changed to GRPC in Lima v1.0, but it was reverted to SSH in v1.0.1 due to stability reasons. The default was further reverted to GRPC in Lima v1.1, as the stability issues were resolved.

Using SSH

SSH based port forwarding was previously the default mode.

To explicitly use SSH forwarding use the below command

LIMA_SSH_PORT_FORWARDER=true limactl start

Advantages

• Outperforms GRPC when VSOCK is available

Caveats

• Doesn’t support UDP based port forwarding
• Spawns child process on host for running SSH master.

SSH over AF_VSOCK

If VM is VZ based and systemd is v256 or later (e.g. Ubuntu 24.10+), Lima uses AF_VSOCK for communication between host and guest. SSH based port forwarding is much faster when using AF_VSOCK compared to traditional virtual network based port forwarding.

To disable this feature, set LIMA_SSH_OVER_VSOCK to false:

export LIMA_SSH_OVER_VSOCK=false

Using GRPC

In this model, lima uses existing GRPC communication (Host <-> Guest) to tunnel port forwarding requests. For each port forwarding request, a GRPC tunnel is created and this will be used for transmitting data

To enable this feature, set LIMA_SSH_PORT_FORWARDER to false:

LIMA_SSH_PORT_FORWARDER=false limactl start

Advantages

• Supports both TCP and UDP based port forwarding
• Performs faster compared to SSH based forwarding, when VSOCK is not available
• No additional child process for port forwarding

Benchmarks

The benchmarks detail above are obtained using the following commands

Host -> limactl start vz

VZ Guest -> iperf3 -s

Host -> iperf3 -c 127.0.0.1 //Benchmark for TCP (average of "sender" and "receiver")
Host -> iperf3 -c 127.0.0.1 -R //Benchmark for TCP Reverse (same as above)