How to SSH Into a Server or OLT

Today I learned how to SSH into a server and an Optical Line Terminal (OLT). This is a fundamental skill for remote server administration and network management.

Basic SSH Command

The basic syntax for SSH is surprisingly simple:

ssh username@hostname

For example:

ssh admin@192.168.1.100

SSH Authentication Methods

I learned there are two main ways to authenticate:

1. Password Authentication: Simply enter your password when prompted
2. Key-Based Authentication: More secure, uses a public/private key pair

Setting Up Key-Based Authentication

To set up key-based authentication:

# Generate SSH key pair
ssh-keygen -t rsa -b 4096

# Copy public key to server
ssh-copy-id username@hostname

SSH into an OLT

Connecting to an OLT (Optical Line Terminal) has some specific considerations:

1. Default Credentials: Many OLTs have default credentials like admin/admin or root/admin
2. Telnet vs SSH: Older OLTs might only support Telnet (less secure)
3. Port Differences: Some OLTs use non-standard SSH ports

Example command for connecting to an OLT:

ssh -p 22 admin@192.168.1.10

Useful SSH Commands Once Connected

Once connected to a server or OLT, these commands came in handy:

# View system information
uname -a

# Check running processes
ps aux

# View network interfaces
ifconfig

# For OLTs: Show connected ONUs
show pon onulist

# For OLTs: Check optical power levels
show pon power-info

SSH Configuration Tips

I also learned some useful SSH configuration tricks:

1. Config File: Create ~/.ssh/config to store connection settings
2. Connection Persistence: Use ServerAliveInterval 60 to keep connections alive
3. Aliases: Set up shortcuts for frequent connections

Example config file:

Host myserver
    HostName 192.168.1.100
    User admin
    Port 22
    IdentityFile ~/.ssh/id_rsa
    ServerAliveInterval 60

Then simply use:

ssh myserver

Security Best Practices

Important security considerations:

1. Disable Password Authentication when possible
2. Use Strong Keys (RSA 4096 bits or ED25519)
3. Change Default Ports to reduce automated attacks
4. Implement Fail2Ban to prevent brute force attempts
5. Keep Software Updated to patch security vulnerabilities

SSH is an incredibly powerful tool for remote administration. I’m glad I took the time to learn it properly!