Git once configured ssh after modification at home, and then returned to the company to use git and could not use it.

  git, question
The operation steps are as follows
 1, git add .
 2. git commit -m 'modify'
 3. git fetch origin
 
 
 This step reports this mistake.
 $ git fetch origin
 ssh: connect to host  github.com port 22: Connection timed out
 fatal: Could not read from remote repository.
 Please make sure you have the correct access rights and the repository exists.
 
 Please help

Add the native ssh public key to git library.