SSH相关技术问题咨询：账号密码查询、隧道失效及端口转发命令解析

Hey there! Let's break down that SSH command step by step so you can wrap your head around it, especially the part that's been confusing you.

First, let's look at the full command you're working with:

ssh -N -L localhost:8000:localhost:80 root@servername

Let's unpack each piece, starting with the part you're stuck on:

The root@servername portion #

This is how you tell SSH which remote server to connect to, and what user account to use for that connection:

• root: This is the username you’re logging in as on the remote server. Root is the administrative account with full system permissions, but you could use any valid user account set up on that server instead.
• servername: This is the address of the remote server—it can be a domain name (like my-server.com), a public/private IP address (like 192.168.1.50), or a local network hostname.

The rest of the command, for context #

To make sure you have the full picture, let's cover the other parameters:

• -N: This tells SSH not to launch a shell session or run any remote commands once connected. It’s purely for setting up and maintaining the port forwarding tunnel—ideal when you don’t need to interact with the server directly.
• -L localhost:8000:localhost:80: This is the local port forwarding rule:
  • localhost:8000: This is the port on your local machine that you’ll use to access the tunnel. For example, if you open http://localhost:8000 in your browser, that traffic gets sent through the SSH tunnel.
  • localhost:80: This is the target on the remote server side. It means "forward all tunnel traffic to port 80 on the remote server’s own localhost" (so whatever web service is running on port 80 of that server).

Why trying root@(dig +short google.com) didn’t work #

When you tried pointing to Google’s servers, it failed for two key reasons:

• Google doesn’t allow public SSH connections to its servers—they don’t expose SSH ports (usually port 22) to random internet users, so you can’t log in as root (or any user) there.
• Even if you could, forwarding traffic to Google’s port 80 wouldn’t help with bypassing your network guard—you likely want to route traffic through a server you control, not Google’s public infrastructure.

A quick note for your network guard experiment #

Local port forwarding like this works by routing your traffic through the encrypted SSH tunnel to the remote server, then out to its destination. If your network guard blocks direct access to certain services, using an SSH tunnel can bypass this because the guard only sees encrypted SSH traffic (which is often allowed on standard port 22).

备注：内容来源于stack exchange，提问作者Devatrish