Fixing "Broken Pipe" SSH Tunnel Disconnects When Connecting via Bastion

If you've ever tried setting up an SSH tunnel to connect through a bastion host, you might have run into this frustrating issue:

client_loop: send disconnect: Broken pipe

This happens after a few minutes of idle time and typically means your SSH tunnel was dropped due to inactivity.

🎯 The Use Case

You're trying to securely forward a local port to Amazon DocumentDB using a bastion host, like this:

ssh -i "my-bastion-host-key-pair.pem" \
    -L 27017:docdb-dima-1.cluster-xxxxxxxxxxxx.us-east-1.docdb.amazonaws.com:27017 \
    [e-mail] -N

It works for a short time, but then—poof! The connection dies with the infamous Broken pipe error.

🛠️ The Problem

SSH connections can be terminated by the server (or an intermediate firewall/NAT/router) if they are idle for too long. This is common in cloud environments where aggressive timeout settings are used to conserve resources.

✅ The Fix

To keep the connection alive, you can configure your SSH client to send periodic keep-alive messages. This is done using two SSH options:

• ServerAliveInterval=60: Sends a keep-alive packet every 60 seconds.
• ServerAliveCountMax=3: If the server doesn't respond to 3 consecutive keep-alive messages, the client will disconnect.

🔐 Updated Command

Here's the improved SSH command with keep-alive settings:

ssh -i "my-bastion-host-key-pair.pem" \
    -o ServerAliveInterval=60 \
    -o ServerAliveCountMax=3 \
    -L 27017:docdb-dima-1.cluster-xxxxxxxxxxxx.us-east-1.docdb.amazonaws.com:27017 \
    [e-mail] -N

This will keep your tunnel alive even during idle periods, and should prevent those unexpected disconnects.

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