Help with Linux and Open Source Software

Ubuntu 16.04 PXE Installs Fail Because it Mangles the Squashfs Path

Trying to set up a network install of Ubuntu 16.04 Xenial? Good luck with that. Looks like a PXE breaking bug has crept in at the last minute.

Posted by Tony on Apr 27, 2016 | Networking, Linux Tricks, PXE, Netboot

Whitelisting IP Address Ranges with iptables and ipset

If you run a firewall you know how important it is to block out the bad guys. Here's how to only allow parts of the world to even talk to you.

Posted by Tony on Feb 25, 2016 | Servers, Network Security, networking

Automatically Create Jira Support Tickets From Network Events

I'm a big fan of Jira for tracking support tickets. It's easy to have certain security events on your network automatically create tickets.

Posted by Tony on Apr 23, 2015 | Networking

Using VLAN's with ISC-DHCP-SERVER

I decided I wanted to provide DHCP to two different VLAN's each with their own subnet, connected to the same network card in my default router. All packets arriving on that network jack are tagged for either one or the other VLAN. Initially I had trouble with the DHCP server only seeing packets on the root eth0 device and ignoring all the packets on the vlan devices (eth0.1 for instance.) There's a couple of changes I had to make for this to work. These instructions assume an Ubuntu server.

Posted by Tony on Feb 28, 2015 | Networking

Linux, iptables, SNAT and Too Many Adapters

I've had some weird glitches with my primary firewall this week. After a reboot, certain SNAT rules just didn't... happen. Or, other SNAT rules did. And it always seemed to only impact SIP traffic. For instance, after rebooting, SIP traffic from one internal phone server that's destined for another internal phone server at the other end of a VPN connection would spontaneously decide to SNAT itself to an external IP address, yet still go across the tunnel. Or, SIP traffic destined for the outside would decide to route correctly out the right adapter, but leave the private address on it, ignoring the SNAT rule I could plainly see in iptables.

Posted by Tony on Feb 19, 2015 | Networking, Network Security, Servers

Configuration of Asus Routers Running Merlin Firmware with OpenVPN

NOTE: This is now outdated and Matthew has emailed me to let me know he'll be doing a new write-up soon. Here's a guest blog post by Matthew Burkett on configuring the Merlin router firmware for OpenVPN.

Posted by Tony on Apr 02, 2014 | Networking

IPTables Trickery

I've had a bit of a strange situation on my network - Googling never did come up with anything for me.

Posted by Tony on Aug 22, 2009 | Servers, Network Security, Networking

Stop Port Scans In Their Tracks With iptables

Sure, there's a lot of tutorials out there for blocking SYN+FIN, christmas scans, etc. But did you know that most of those won't help against a default nmap scan? Try it - block all the standard stealth scans, etc using something like the following...

Posted by Tony on Mar 10, 2009 | Networking, Network Security, Servers