I've been playing around with various DNS setups on Amazon and by far the most annoying part of it all is that I can't tell when the DNS change has propagated to my browser/computer!
ipconfig /flushdns doesn't really seem to consistently do anything (I'm on Windows).
Is there any good way to force a DNS refresh on my development computer so I can test DNS configs more efficiently?
Using CTRL+SHIFT+R to force a hard refresh on the browser seems to work better but it's still not very consistent.
I have been setting TTL to 60 when testing, but it doesn't seem to be reliable.
On chrome you could just flush the dns cache by a click.
chrome://net-internals/#dns
Go to above url in chrome and click the "clear host cache".
I have a slight problem bit of the back story. recently ive been trying to test out univention which is a linux distribution with the goal of being able to replace Microsoft active directory.
I tested it locally and all went reasonably well after a few minor issues i then decided to test it remotely as the company wants to allow remote users to access this so i used myhyve.com to host it and its now been setup successfully and works reasonably well.
however
my main problem is DNS based as when trying to connect to the domain the only way windows will recognize it is by editing the network adapter and setting ip v4 dns server address to the ip address of the server hosting the univention active directory replacement. although this does allow every thing to work its not ideal and dns look up on the internet are considerably longer. i was wondering if any one had any ideas or have done something similar and encountered this problems before and know a work around. i want to avoid setting up a vpn if possible.
after initially registering the computer on the domain i am able to remove the dns server address and just use a couple of amendments to the HOST file to keep it running but this still leads to having issues connecting to the domain controller sometimes and is not ideal. any ideas and suggestions would be greatly received.
.Michael
For the HOST entries, the most likely issue is, that there are several service records a computer in the domain needs. I'm not sure, whether these can be provided via the HOST file or not but you'll definitely have authentication issues if they are missing. To see the records your domain is using issue the following commands on the UCS system.
/usr/share/univention-samba4/scripts/check_essential_samba4_dns_records.sh
For the slow resolution of the DNS records there are several points where you could start looking. My first test would be whether or not you are using a forwarder for the web DNS requests and whether or not the forwarder is having a decent speed. To check if you are using one, type
ucr search dns/forwarder
If you get a valid IP for either of the UCR Variables, dns/forwarder1, dns/forwarder2 or dns/forwarder3, you are forwarding your DNS requests to a different Server. If all of them are empty or not valid IPs then your server is doing the resolution itself.
Not using a forwarder is often slow, as the DNS servers caching is optimized for the AD operations, like the round robin load balancing. Likewise a number of ISPs require you to use a forwarder to minimize the DNS traffic. You can simply define a forwarder using ucr, I use Google on IPv4 for the example
ucr set dns/forwarder1='8.8.8.8'
The other scenario might be a slow forwarder. To check it try to query the forwarder directly using the following command
dig univention.com #(ucr get dns/forwarder1)
If it takes long, then there is nothing the UCS server can do, you'll simply have to choose a different forwarder from the ucr command above.
If neither of the above helps, the next step would be to check whether there are error messages for the named daemon in the syslog file. Normally these come when you are trying to manually remove software or if the firewall configuration got changed.
Kevin
Sponsored post, as I work for Univention North America, Inc.
I have a debian 7.5 based Ubuntu server, apache 2.2.22.
It's a rather vanilla installed XAMP used as a basic web server.
It used to work fine and I have no idea why it stopped working suddenly (there was some maintenance today but it worked when I left it - I changed partition sizes with Gparted).
When I try to access a website from the server (tried with w3m) all is working OK, including PHP and MySQL access.
When I try to access the same host (using a domain) from the outside, the browser keeps loading for a long while, eventually (after few minutes) saying the page could not be loaded.
I made sure that ports are open and accessible with outside scanner.
So I'm sure the Apache is available (working from inside the network, websites loading from SSH using w3M and pinging)
I'm sure the server is connected to the web (I can use putty to SSH)
the host is resolving to the correct IP (but won't ping from outside, only inside)
The ports seems to be opened (scanned and got OK for port 80)
I'm not a professional IT, so If there is info I can add that could help just ask away.
would really appreciate any idea or direction.
Thanks!
I still suspect the UFW/iptables firewall is blocking all incoming connections... Please go through this article and double check
http://www.cyberciti.biz/faq/ubuntu-server-disable-firewall/
If you're sure that the firewall config is OK, please try packet capturing with Wireshark to see what's going on underneath.
http://www.youtube.com/watch?v=sOTCRqa8U9Y How to install
Thanks for the help,
Oddly enough - It just started working again after 12 hours of not working.
A friend of mine, an IT person just called to try and help, and he simply connected (5 mins after I tried) and said it's all working for him.
I tried, and it's working for me also.
Have no idea why it stopped working, and why it is working now.
I think it might be an ISP problem or a router issue... The server is in our offices so I guess it could be both. I just don't understand why SSH would work and HTTP wouldn't.
I'm having some problems with switching between servers using ssh, on my universitys Linux servers.
The servers I'm using are set up such that I am sent to an initial login server once I run ssh ...#login.... from my terminal. As the login-server is not meant for heavy computations I usually switch to another server after login, by simply writing that server's name. However, this server is full at times (since a lot of different people are using it), and I'd like to switch to another server at the same network. The problem is that I don't know any of the other servers' names, so I'm looking for a command to list all available servers from the login-server.
Possible with NMAP, I am not an NMAP expert but hopefully you can take a look and get it working for you.
http://www.commandlinefu.com/commands/view/6853/get-a-list-of-ssh-servers-on-the-local-subnet
The bottom option:
nmap -p 22 --open -sV XX.XX.XX.XX/XX
will scan for port 22 being open displaying the Version number across the IP subnet range...I would recommend better understanding nmap. Hope it at least gets you started! You could always ask your universities IT dept for a list of server names as a shortcut...
I'd like to set up a cheap Linux box as a web server to host a variety of web technologies (PHP & Java EE come to mind, but I'd like to experiment with Ruby or Python in the future as well).
I'm fairly versed in setting up Tomcat to run on Linux for serving up Java EE applications, but I'd like to be able to open this server up, even just so I can create some tools I can use while I am working in the office. All the experience I've had with configuring Java EE sites has all been for intranet applications where we were told not to focus on securing the pages for external users.
What is your advice on setting up a personal Linux web server in a secure enough way to open it up for external traffic?
This article has some of the best ways to lock things down:
http://www.petefreitag.com/item/505.cfm
Some highlights:
Make sure no one can browse the directories
Make sure only root has write privileges to everything, and only root has read privileges to certain config files
Run mod_security
The article also takes some pointers from this book:
Apache Securiy (O'Reilly Press)
As far as distros, I've run Debain and Ubuntu, but it just depends on how much you want to do. I ran Debian with no X and just ssh'd into it whenever i needed anything. That is a simple way to keep overhead down. Or Ubuntu has some nice GUI things that make it easy to control Apache/MySQL/PHP.
It's important to follow security best practices wherever possible, but you don't want to make things unduly difficult for yourself or lose sleep worrying about keeping up with the latest exploits. In my experience, there are two key things that can help keep your personal server secure enough to throw up on the internet while retaining your sanity:
1) Security through obscurity
Needless to say, relying on this in the 'real world' is a bad idea and not to be entertained. But that's because in the real world, baddies know what's there and that there's loot to be had.
On a personal server, the majority of 'attacks' you'll suffer will simply be automated sweeps from machines that have already been compromised, looking for default installations of products known to be vulnerable. If your server doesn't offer up anything enticing on the default ports or in the default locations, the automated attacker will move on. Therefore, if you're going to run a ssh server, put it on a non-standard port (>1024) and it's likely it will never be found. If you can get away with this technique for your web server then great, shift that to an obscure port too.
2) Package management
Don't compile and install Apache or sshd from source yourself unless you absolutely have to. If you do, you're taking on the responsibility of keeping up-to-date with the latest security patches. Let the nice package maintainers from Linux distros such as Debian or Ubuntu do the work for you. Install from the distro's precompiled packages, and staying current becomes a matter of issuing the occasional apt-get update && apt-get -u dist-upgrade command, or using whatever fancy GUI tool Ubuntu provides.
One thing you should be sure to consider is what ports are open to the world. I personally just open port 22 for SSH and port 123 for ntpd. But if you open port 80 (http) or ftp make sure you learn to know at least what you are serving to the world and who can do what with that. I don't know a lot about ftp, but there are millions of great Apache tutorials just a Google search away.
Bit-Tech.Net ran a couple of articles on how to setup a home server using linux. Here are the links:
Article 1
Article 2
Hope those are of some help.
#svrist mentioned EC2. EC2 provides an API for opening and closing ports remotely. This way, you can keep your box running. If you need to give a demo from a coffee shop or a client's office, you can grab your IP and add it to the ACL.
Its safe and secure if you keep your voice down about it (i.e., rarely will someone come after your home server if you're just hosting a glorified webroot on a home connection) and your wits up about your configuration (i.e., avoid using root for everything, make sure you keep your software up to date).
On that note, albeit this thread will potentially dwindle down to just flaming, my suggestion for your personal server is to stick to anything Ubuntu (get Ubuntu Server here); in my experience, the quickest to get answers from whence asking questions on forums (not sure what to say about uptake though).
My home server security BTW kinda benefits (I think, or I like to think) from not having a static IP (runs on DynDNS).
Good luck!
/mp
Be careful about opening the SSH port to the wild. If you do, make sure to disable root logins (you can always su or sudo once you get in) and consider more aggressive authentication methods within reason. I saw a huge dictionary attack in my server logs one weekend going after my SSH server from a DynDNS home IP server.
That being said, it's really awesome to be able to get to your home shell from work or away... and adding on the fact that you can use SFTP over the same port, I couldn't imagine life without it. =)
You could consider an EC2 instance from Amazon. That way you can easily test out "stuff" without messing with production. And only pay for the space,time and bandwidth you use.
If you do run a Linux server from home, install ossec on it for a nice lightweight IDS that works really well.
[EDIT]
As a side note, make sure that you do not run afoul of your ISP's Acceptable Use Policy and that they allow incoming connections on standard ports. The ISP I used to work for had it written in their terms that you could be disconnected for running servers over port 80/25 unless you were on a business-class account. While we didn't actively block those ports (we didn't care unless it was causing a problem) some ISPs don't allow any traffic over port 80 or 25 so you will have to use alternate ports.
If you're going to do this, spend a bit of money and at the least buy a dedicated router/firewall with a separate DMZ port. You'll want to firewall off your internal network from your server so that when (not if!) your web server is compromised, your internal network isn't immediately vulnerable as well.
There are plenty of ways to do this that will work just fine. I would usually jsut use a .htaccess file. Quick to set up and secure enough . Probably not the best option but it works for me. I wouldn't put my credit card numbers behind it but other than that I dont really care.
Wow, you're opening up a can of worms as soon as you start opening anything up to external traffic. Keep in mind that what you consider an experimental server, almost like a sacrificial lamb, is also easy pickings for people looking to do bad things with your network and resources.
Your whole approach to an externally-available server should be very conservative and thorough. It starts with simple things like firewall policies, includes the underlying OS (keeping it patched, configuring it for security, etc.) and involves every layer of every stack you'll be using. There isn't a simple answer or recipe, I'm afraid.
If you want to experiment, you'll do much better to keep the server private and use a VPN if you need to work on it remotely.