# SSH Setup for the Yen Servers

When working on the Yen cluster, you may occasionally open multiple SSH sessions from your local computer or connect from one Yen node to another to check a running process or run a command on a different node.

You can make these workflows smoother by configuring SSH multiplexing on your local computer and setting up **SSH key authentication** between Yen nodes.

## Local SSH Multiplexing for the Yens

On your local computer, add or merge the following settings into `~/.ssh/config`. This lets SSH reuse an existing authenticated connection when you open additional `ssh`, `scp`, or `rsync` sessions to the Yen servers.

Local ~/.ssh/config

```
IgnoreUnknown GSSAPIKeyExchange

Host yen yen? yen??
  HostName %h.stanford.edu

Host yen yen.stanford.edu yen? yen?? yen?.stanford.edu yen??.stanford.edu
  HostKeyAlias yen.stanford.edu

Host yen yen.stanford.edu yen? yen?? yen?.stanford.edu yen??.stanford.edu
  ControlMaster auto
  ControlPersist yes
  GSSAPIDelegateCredentials yes

Host *
  ControlPath ~/.ssh/%r@%h:%p
  GSSAPIKeyExchange yes
  GSSAPIAuthentication yes
  ServerAliveInterval 60
```

After this is configured, the first connection still requires normal authentication, but later connections can reuse the existing control connection while it persists.

## Passwordless SSH Between Interactive Yen Nodes

To follow the steps below, first open a terminal on an [interactive Yen node](/_getting_started/yen-servers/#how-to-connect).

### Step 1 — Create a Dedicated SSH Key

Create a key specifically for connecting between Yen nodes.

Create a new SSH key for Yen nodes

```
ssh-keygen -t ed25519 -f ~/.ssh/yen_ed25519 -C "$USER@yens"
```

This creates:

SSH key files created

```
~/.ssh/yen_ed25519
~/.ssh/yen_ed25519.pub
```

### Step 2 — Add the Key to `authorized_keys`

Allow this key to authenticate your account:

Add your public key to authorized_keys

```
cat ~/.ssh/yen_ed25519.pub >> ~/.ssh/authorized_keys
```

### Step 3 — Configure SSH for Yen Nodes

Create an SSH configuration so the correct key is automatically used.

Configure SSH for yen1–yen5

```
cat > ~/.ssh/config <<EOF
Host yen1 yen2 yen3 yen4 yen5
    IdentityFile ~/.ssh/yen_ed25519
    IdentitiesOnly yes
    GSSAPIAuthentication no
EOF
```

### Step 4 — Test the Connection

Try connecting to another Yen node:

Test passwordless SSH

```
ssh yen3
```

If the setup is successful, you should connect without being prompted for a password.