There's a Boston customer I have serviced for many years now.
They run Unix, so there's never much to do (we Unix folk
have less work than Maytag repairmen), but some years ago
I had put in a small Linux server just so that some of their
order entry folks could ssh in from home and then telnet to
the SCO box that their app runs on. That's been chugging
along for many a year on a DSL line.
Recently they decided that they needed faster Internet access
and their own mail server. That seemed like the ideal time to
upgrade the Linux server and install Kerio Mailserver.
The old Linux was setup as a gateway: one nic had the public ip
that they would ssh to. I really do not like this configuration:
I prefer hardware firewalls. As mentioned elsewhere, I also
firewalls; that is, I have the hardware firewall forwarding
the ports I want inward but at the Linux box I also specifically both
disable and block all ports not being used.
So, on the day of the switch-over, I brought a hardware firewall
and Suse Linux CD's. I first configured the firewall from information
Conversent and tested it with my laptop.
By the way, let me put in a plug here. I've done quite a few
turnups with customers using Conversent and my experience with them
really has been excellent. Support has responded quickly, accurately
and intelligently every time I have had a problem. They really
get high marks in my book. No, I'm not a reseller and I get nothing
for saying that.
Anyway, that worked fine, so I took down the old Linux box, wired in
the router and had everyone reacquire DHCP from it so that they
wouldn't lose Internet access while I loaded Suse. I did a straight
text install and did not install any desktop - this is a server, it doesn't
need a GUI.
I configured the firewall to forward tcp ports 22 and 25 to my new Suse box.
I then downloaded Kerio Mailserver and installed that. The RPM
failed however because it needed libstdc++, which was not installed.
I had a little difficulty figuring out what rpm was actually needed; it
turns out to be compat-libstdc++. After that, Kerio ran fine.
To test, I ssh'd out to my own web site and tried telneting back to port
25. Hmm.. no response. I double checked "lsof -i:25" on the Suse,
Kerio definitely was running.
Oh duh! Forgot the Suse Firewall. I added
to /etc/sysconfig/SuSEfirewall2, restarted the firewall (/etc/init.d/SuSEfirewall2_init restart) and tried again.
OK, maybe there's something wrong at the firewall. I reconfigured it to
send 22 to my laptop's IP and opened ssh on it. Nope, that didn't work
either. It was starting to feel like it was time to check with Conversent,
so I called and explained what was happening.
The tech I got checked and said everything looked fine.. maybe I had
a bad firewall?
Yeah, maybe. But I reconfigured my Mac with the static IP and
tried again. No firewall now, just my Mac hooked right up to the
Adtran. Still did not work.
Ok, deep breaths. There has to be a reason. I started looking
at network status from the external machine and immediately noticed
something odd. My public ip was a 72. address, but my box said I
had connected from a 209. address. That couldn't be right, so
I called Conversent again. Yep, that's the way we do it, he said. Your
router is bad.
Naaw. Can't be. You've NATted me, I thought. I hung up and
called back again to get a different tech.
This women listened to what I said and immediately said "Sure -
we must have left NAT on. I'll fix it.". Sure enough, mere
seconds later I could ssh to my Mac. I disconnected, reconnected
the firwall, reconfigured that and tried a telnet to port 25. Success!
I then tried an ssh to the public ip. Oops: permission denied.
Well, gosh, I had forgotten to uncomment "PasswordAuthentication yes"
in /etc/ssh/sshd_config. I did that and a
"kill -1 `cat /var/run/sshd.init.pid`" set it working as I needed. I
also denied root login while I was there and set MaxStartups 10:30:60
also. I'd rather use public keys but the remote users don't all have software
that can do that.
All's well that ends well.
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© 2009-11-07 Anthony Lawrence