For some users resident in a very restricted network environment, we have opened port 80 and 443 for ssh on linux1.

You can now connect to linux1 by
$ ssh user@linux1.csie.ntu.edu.tw -p 80
or
$ ssh user@linux1.csie.ntu.edu.tw -p 443
and then access other machines, do ssh port-forwarding.

linux1 now accepts ssh connection from port 80 and 443