Using Squid to filter Internet access
ACLs – Time Based
Restricting access by time is an especially useful feature of Squid for kids. Virtually every computing device now has WiFi, and I suspect at some point WiFi-capable devices will become cheap enough to give away in cereal packets. Given this trend, it seems clear that I won't be catching my kids hiding under their blankets reading a book with a flashlight; instead, they'll be surfing the web or playing online games.
To restrict web access on weekdays and leave it more open on weekends, you can use rules such as:
acl basic time MTWHF 18:00-20:00 acl basic time SA 9:00-20:00
These lines would set an ACL that allows traffic Monday through Friday from 6pm until 8pm, and on Saturday and Sunday from 9am until 8pm.
ACLs – URL Based
Squid really shines in the variety of ways it allows you to filter. For example, you can filter access based on source and destination IP, on the domain of the client, the destination domain of the request, regular expression versions of these domains, the URL, the URL excluding the protocol and hostname, and the HTTP method (GET, PUT, POST), just to name a few. One way to make all this more manageable is to use include files:
acl good_domains dstdomain "/etc/squid/good_domains.acl"
The named file would then contain entries such as
.wikipedia.org .linux-magazine.com
and so on. Basically, for any ACL type, you can use an external file. I strongly recommend doing so, because it makes things much more manageable.
Restricting by File Type and Mime Type
Some things never get old, and apparently serving malware in the form of hostile executables or files such as PDFs is still a popular and effective way to attack users. You can block files based on the urlpath_regex
, usually by blocking the file extension. However, some operating systems and applications will still load content, even if the file extensions are "wrong," so you should also block by mime type, just to be on the safe side. To block Flash videos, for example, you can do:
acl flashvideo rep_mime_type video/flv video/x-flv acl flashvideo urlpath_regex \.flv(\?.*)?$
Using Squid ACLs does have some down sides, however. For one thing, you'll need to maintain files manually and reload Squid every time you update them. To deal with this, you can use the ICAP protocol.
« Previous 1 2 3 Next »
Buy this article as PDF
(incl. VAT)
Buy Linux Magazine
Subscribe to our Linux Newsletters
Find Linux and Open Source Jobs
Subscribe to our ADMIN Newsletters
Support Our Work
Linux Magazine content is made possible with support from readers like you. Please consider contributing when you’ve found an article to be beneficial.
News
-
Endless OS 6 has Arrived
After more than a year since the last update, the latest release of Endless OS is now available for general usage.
-
Fedora Asahi 40 Remix Available for Macs with Apple Silicon
If you've been anticipating KDE's Plasma 6 for your Apple Silicon-powered Mac, then you're in luck.
-
Red Hat Adds New Deployment Option for Enterprise Linux Platforms
Red Hat has re-imagined enterprise Linux for an AI future with Image Mode.
-
OSJH and LPI Release 2024 Open Source Pros Job Survey Results
See what open source professionals look for in a new role.
-
Proton 9.0-1 Released to Improve Gaming with Steam
The latest release of Proton 9 adds several improvements and fixes an issue that has been problematic for Linux users.
-
So Long Neofetch and Thanks for the Info
Today is a day that every Linux user who enjoys bragging about their system(s) will mourn, as Neofetch has come to an end.
-
Ubuntu 24.04 Comes with a “Flaw"
If you're thinking you might want to upgrade from your current Ubuntu release to the latest, there's something you might want to consider before doing so.
-
Canonical Releases Ubuntu 24.04
After a brief pause because of the XZ vulnerability, Ubuntu 24.04 is now available for install.
-
Linux Servers Targeted by Akira Ransomware
A group of bad actors who have already extorted $42 million have their sights set on the Linux platform.
-
TUXEDO Computers Unveils Linux Laptop Featuring AMD Ryzen CPU
This latest release is the first laptop to include the new CPU from Ryzen and Linux preinstalled.