networking-mosh-resilient-ssh

name	networking-mosh-resilient-ssh
description	Connecting over unreliable networks (mobile, WiFi)

Mosh - Resilient SSH Alternative

Use this skill when:

• Connecting over unreliable networks (mobile, WiFi)
• Working with high-latency connections
• Needing to survive network disconnects
• Roaming between networks while maintaining sessions
• Improving SSH user experience

Installation

# macOS
brew install mosh

# Ubuntu/Debian
sudo apt install mosh

# Server must also have mosh installed

Basic Usage

# Instead of SSH
ssh user@server

# Use Mosh
mosh user@server

# With specific port
mosh --ssh="ssh -p 2222" user@server

# With different mosh port range
mosh -p 60001 user@server

Key Features

Survives Disconnects

# Start mosh session
mosh user@server

# Network disconnects (sleep laptop, switch WiFi)
# Session continues when network returns

# Compare to SSH:
# ssh user@server
# [network disconnect]
# -> Connection lost, need to reconnect

Local Echo

Mosh predicts typing locally

No lag when typing even on high-latency links

Underlined text = predicted (not yet confirmed by server)

Normal text = confirmed by server

IP Roaming

# Start mosh on WiFi
mosh user@server

# Switch to cellular
# Session continues seamlessly

# SSH would require reconnect

Configuration

Server Setup

# Open UDP ports (mosh uses 60000-61000 by default)
sudo ufw allow 60000:61000/udp

# Or specific range
sudo ufw allow 60001/udp

Custom Port Range

# Server: restrict port range
export MOSH_SERVER_PORT_RANGE=60001-60010

# Client: use restricted range
mosh -p 60001 user@server

Advanced Usage

With Tailscale

# Use mosh over Tailscale
mosh user@100.64.0.5

# Benefits:
# - Encrypted by Tailscale
# - No need to open ports publicly
# - Resilient connection

SSH Configuration

# ~/.ssh/config
Host myserver
    HostName server.example.com
    User myuser
    Port 2222

# Now use
mosh myserver

Tmux Integration

# Ultimate resilient setup
mosh user@server -- tmux attach

# Benefits:
# - Mosh handles network disruption
# - Tmux persists session on server
# - Can disconnect mosh and reconnect to same tmux

Limitations

Not for File Transfers

# ❌ Can't use scp/rsync over mosh
# Mosh is terminal-only

# ✅ Use SSH for file transfers
scp file.txt user@server:

# Or rsync
rsync -avz --progress file.txt user@server:

Port Requirements

Mosh needs UDP ports open

Some restrictive networks block UDP

Fallback to SSH if UDP blocked

Comparison

SSH:

- Works everywhere (TCP port 22)

- File transfers (scp/sftp)

- Port forwarding

- Breaks on network change

Mosh:

- Survives disconnects

- IP roaming

- Low-latency typing

- Requires UDP ports

- Terminal only

Related Skills

• tailscale-vpn.md - Use mosh over Tailscale
• secure-networking.md - Overall networking patterns