Question

Slow ssh connection Ubuntu ws -> server

Asked by: obg

I have my own server (ubuntu 9.04) which communicates without any problems with the Internet and with my Windows client. Then I have Ubuntu desktop on a wireless laptop, which does the same, but when I ssh och scp to the server, first it takes about 6-10 seconds to login, and the transfer rate is about 150 kB/s. http connection speed is a bit higher but far from satisfying. My wireless ling reports good connection 42-56 Mbps.

This is very frustrating as I am rather familiar with Linux but here I don't even know where to begin to look. I suspect some reverse lookup issue, which I managed to solve a couple of years ago, but I haven't been able to figure this one out...

IPv6 is disabled!

Please, could someone point me in the right direction?

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Asked On
2009-09-12 at 12:08:26ID24727084
Tags

slow connection

,

ubuntu

,

linux

,

networking

Topics

Linux Networking

,

Ubuntu

,

Linux Setup

Participating Experts
2
Points
500
Comments
4

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Answers

 

by: nabeelmoiduPosted on 2009-09-12 at 12:12:23ID: 25317534

slow initial login could be due to reverse dns issues..In file /etc/ssh/sshd_config:
UseDNS no

slow transfer rates could be due to tcp window sizes...try altering the sysctl parameters 

 

by: cybervzhn_techPosted on 2009-09-12 at 13:45:12ID: 25317831

Another easy way to resolve the reverse lookup issue is to make /etc/hosts entries for the IPs you ssh from and make sure the "hosts:" line in /etc/nsswitch.conf has "files" listed before "dns". (i.e.  "hosts:    files dns").  Be careful with the /etc/nsswitch.conf file, as changing other lines incorrectly can cause problems.

This problem is caused by ssh'ing locally from your internal network which is usually private IP addresses (i.e. 192.168.x.x, 10.x.x.x, or 172.16.x.x - 172.31.x.x) and not resolvable via DNS unless you run your own internal DNS server with a reverse IP zone for your local private subnet.

Another recommendation I would make, would be to install Denyhosts if you expose ssh to your internet connection so you can connect via SSH from the Internet.  Denyhosts will prevent password attacks of your SSH server from the Internet by denying access to anyone that tires to log in to restricted logins or repeatedly tries to log in with the wrong password.  Add your internal IPs to the "allowed-hosts" file to prevent yourself from being locked out.  The documentation for Denyhosts will help with this.

Regards

 

by: obgPosted on 2009-09-14 at 01:32:04ID: 31628295

Thank you very much! It was a rather simple fix. Sorry it took so long to verify... Now the xfer rate is about 1.1 MB/s which still feels a bit low for a 54 Mbps connection. (Behind the router it's 100 Mbps.) Still I think this is acceptable, and a whole lot better.

Why would I need to install a "denyhosts" package as the hosts.deny is there by default...?

 

by: obgPosted on 2009-09-14 at 01:40:55ID: 25323634

Sorry nabeelmoidu, I don't want to disable DNS. The next expert with the strange name came up with exactly the solution I was looking for. For some reason my nsswitch.conf was corrupt. I will experiment a bit with the sysctl parameters though.

20120131-EE-VQP-002

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