问题
When I ping my server, it responds:
user@localhost:~$ ping my.server
PING my.server (111.111.111.11) 56(84) bytes of data.
64 bytes from my.server (111.111.111.11): icmp_req=1 ttl=42 time=38.4 ms
64 bytes from my.server (111.111.111.11): icmp_req=2 ttl=42 time=50.0 ms
64 bytes from my.server (111.111.111.11): icmp_req=3 ttl=42 time=58.6 ms
^C
--- my.server ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2003ms
rtt min/avg/max/mdev = 38.419/49.037/58.637/8.287 ms
but when I try to ssh (something that I always do, and have been doing for the past few hours on the same connection), it hangs:
user@localhost:~$ ssh my.server
http://speedtest.net says that my connection has 1.5 Mbps download and 0.4 Mbps upload speed.
Is there a reason that ssh hangs?
Results from suggestions provided in answers
from @nsfyn55
user@localhost:~$ telnetmy.server 22
Trying 111.111.111.11...
Connected to my.server
Escape character is '^]'.
SSH-2.0-OpenSSH_4.3
Connection closed by foreign host.
from @vahid:
user@localhost:~$ nc -v -w 1 111.111.111.111 -z 22
nc: timeout cannot be negative
回答1:
ping (ICMP protocol) and ssh are two different protocols.
It could be that ssh service is not running or not installed
firewall restriction (local to server like iptables or even sshd config lock down ) or (external firewall that protects incomming traffic to network hosting 111.111.111.111)
First check is to see if ssh port is up
nc -v -w 1 111.111.111.111 -z 22
if it succeeds then ssh should communicate if not then it will never work until restriction is lifted or ssh is started
回答2:
Find out two pieces of information
- Whats the hostname or IP of the target ssh server
- What port is the ssh daemon listening on (default is port 22)
$> telnet <hostname or ip> <port>
Assuming the daemon is up and running and listening on that port it should etablish a telnet session. Likely causes:
- The ssh daemon is not running
- The host is blocking the target port with its software firewall
- Some intermediate network device is blocking or filtering the target port
- The ssh daemon is listening on a non standard port
- A TCP wrapper is configured and is filtering out your source host
回答3:
On the server, try:
netstat -an
and look to see if tcp port 22 is opened (use findstr in Windows or grep in Unix).
来源：https://stackoverflow.com/questions/12715233/why-can-i-ping-a-server-but-not-connect-via-ssh