网络设置更改后，Linux Debian SSH与另一台计算机的连接已延迟

Question

Hi StackOverflow members,

I have an issue with ssh connection on my Debian 7 system to a remote OpenSSH server located on the same network. It looks like there is some network configuration problem but I cann't find where it lays. This two debian machines are connect with a switch that is NOT connected to a router. So the two machines have no internet connection.

A-Debian 7
IP: 192.168.1.2
MASK: 255.255.255.0
GW: 192.168.1.1

B-Debian 7
IP: 192.168.1.3
MASK: 255.255.255.0
GW: 192.168.1.1

With that configuration the ssh command prompts my for a password in less then a second. But the with the following network configuration I get the password prompt after a 10+ second delay:

A-Debian 7
IP: 10.10.1.83
MASK: 255.255.255.128
GW: 10.10.1.1

B-Debian 7
IP: 10.10.1.82
MASK: 255.255.255.128
GW: 10.10.1.1

The ssh connection from the server A -> B runs with both configs on custom 1111 port. The B machine has also a Web server running on port 8080 that has no delays with both net configurations.

Thank you in advance for any clues or tips how to solve that problem.

SOLVED: Removing of the gateway parameter "GW: 10.10.1.1" in the network settings has solved the problem.

Answer 1

The usual culprits here are IPv6 and DNS lookups.

SSH might try to connect via IPv6, first, but the timeout is too low for that. You can see whether IPv6 is enabled with

cat /proc/sys/net/ipv6/conf/eth0/disable_ipv6

To disable:

echo 1 > /proc/sys/net/ipv6/conf/eth0/disable_ipv6

The second culprit is DNS; my guess is that DNS lookups don't work correctly with the second configuration. Try host www.google.com to test this theory.

If that also has a delay, you need to fix your DNS setup.

If that's not it, check the rest of your networking parameters: Gateway, cables, etc.

Start to ping the other host. Is that fast & reliable?

Next, try remote login ( ssh , telnet ). Note that you can give telnet a port to connect to, so if you have DB server running, you can still use telnet to connect to the server. It will print an error but it allows you to test the TCP/IP connection without any extra error sources.