Implementing a Linux print server with CUPS

Recently we've been having trouble with the reliability of our Windows 2000 based print server. Print jobs were becoming stuck in the queue. Typically this had to start happening the week when all the students need to print out their coursework. Murphy's law strikes again. *sigh*

Anyway, I elected to press one of our spare Linux boxes into service as a temporary print server and migrate to it room by room. I chose to use one of our spare AMD64 based standalone server machines (previously used as a temporary server for our VLE).

On the software side of things I used the following:

Ubuntu Linux 6.06 LTS (Server Install)
CUPS
Samba + Winbind
GhostScript ESP

On the printer side of things we mainly have Brother based printers. They generally fall into two categories. Either they support Postscript or they are GDI printers and require a Foomatic driver (the Brother HL1250 driver) to work. There's also a HP 4000 Laserjet and a Lanier photocopier. Both of these print fine with PCL6.

There were a couple of hiccups when configuring the print server. The general procedure is the configure CUPS then try and print from that. Then once CUPS works attempt to hook Samba up to the CUPS back end and print via Samba from a Windows PC. Apart from some stupid mistakes typoing IP addresses configuring CUPs there was no problems getting CUPS to print.

Things got a little more involved on the Samba side of the equation. Firstly I misread the documentation and didn't realise I needed the Postscript driver from Windows. Secondly I had no admin access to the print server from Windows because the default group for 'Administrator' was set to 'Domain Users' rather than 'Domain Admins'. Finally, because Samba was running as a member server on a domain I couldn't log in as 'root', I finally figured out I had to use 'localmachine\root' for my login to work. All of these little hang ups are obvious in hindsight, but they did cause me some serious confusion at the time.

I'm currently in the process of moving the client machines over to the new print server. I've had no complaints of strange or missing printouts so it looks like things are going well.

Security through Obscurity

This is a follow up to my 'The trouble with NAT' post. I thought I should explain the other aspect to the thread that surfaced as it progressed as it touch on some other very interesting (and apparently controversial) points of view. As I previously explained the original poster of the thread had hit a brick wall in attempting to access a website. If you want to know the full details of why and how you really should read my previous blog entry. If not then read on.

After a while a possible solution emerged to the IP ban. Use an anonymous proxy. There is however a catch with that. Most educational institutions use web filtering software to block certain categories of websites. There's the usual obvious stuff like porn, warez, gambling etc. But most also attempt to block sites that have Trojans/viruses and most relevant for our situation sites that allow users to bypass the filtering. The vast majority of these only filter based on the sites domain or the URL.

This is hopelessly inflexible. Your fighting a losing battle trying to keep up with all the new sites going up on a daily basis. No, a much more sensible and proven method is to filter based on the content of the actual web pages. This how your virus scanner and spam filter works after all! To that end I use a web filter called DansGuardian. It does domain, URL and content filtering plus it can scan for viruses.

However it seems quite a few schools are using inferior systems (and paying for them to boot!). This got me into a little trouble and a few flames. When I pointed out that the original poster could setup a simple PHPProxy based system that would solve his problem my post was moderated. Now as far I'm concerned there really isn't any point.

Not withstanding the fact PHPProxy had been mentioned previously to illustrate exactly the problems I've outlined. I feel that the tools themselves are not to blame. There always will be someone out there who wishes to take freely available information and do something harmful or illicit on their work/school/college network. You just have to prepare your systems as secure as possible and have monitoring systems in place to catch them. Assuming you do then hope your AUP is sufficient to deal with them when you catch them.

The trouble with NAT

There was a forum topic earlier this week on Edugeek (a very good site, recommended) concerning a user who was at college and he had lost access to some online forums. This was because his college uses NAT to allow the many PC's on their private LAN to access the Internet simultaneously. The forum admins had banned the IP of the problem user but because all the users at the college appear as coming from one IP the forum admins had effectively banned the entire college from their site. Naturally he had contacted the admins to re-establish access. They apparently declined.

I personally have seen the same problem on Wikipedia. IP bans are quite common for 'anonymous' editors who vandalise and blank pages. In fact I raised this issue not long ago with our LEA because the proxy servers the schools used were blocked from editing. There is little that they can do of course. Happily with Wikipedia it's possible to get round the editing ban by creating a user account. Any edits will then be attributed to the account and not the IP even the IP is blocked from editing.

I suspect NAT will be with us for a long time to come and this is one of many unfortunate side effects. Of course it has it's advantages for sharing the Internet and providing security for machines behind the NAT gateway. But it really isn't the way the Internet is supposed to work. A lot of software (Video conferencing, Instant Messaging, VoIP, P2P apps like Bit torrent for example) assumes end to end compatibility which has to be hacked around to work with NAT.

Roll on IPv6!