Originally published at tolaris.com. You can comment here or there.

I’m an IP network engineer. When something goes wrong, the first thing I do is sniff packets. Got a SIP phone that won’t register? Forget reading logs; sniff 5060/udp and read the SIP chatter directly. A customer complains that “Yahoo chat doesn’t work”? Sniff 5050/tcp and look for ( Read more... )

Originally published at tolaris.com. You can comment here or there.

Not long ago we started having very unusual issues our email servers. Mail would be inexplicably held for delivery, bounce back, or fail to send for hours and then send without issue later. Some users couldn’t fetch email by POP until they restarted their mail client. We ( Read more... )

Originally published at tolaris.com. You can comment here or there.

I use iptables firewalls on every server I administer, including all of our core routers (which run Linux too). There are lots of tools to easily configure a firewall. For simple tasks, Ubuntu now installs ufw by default, which has both command-line and GUI tools. For servers, ( Read more... )

Originally published at tolaris.com. You can comment here or there.

I try to post a few times each month, but somehow January (and most of February) fell through the cracks. Lately I’ve been busy with operational tasks, which hasn’t left me much room for engineering. I haven’t solved any particularly hard or unusual problems, which is usually what ( Read more... )

Originally published at tolaris.com. You can comment here or there.

We run several virtual machine host servers on a network with multiple VLANs. The virtual machines are members of different VLANs, but are not themselves aware of the VLAN. This is how we did it.

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Originally published at tolaris.com. You can comment here or there.

After my recent adventure with reverse-path filtering, I didn’t expect to see it again so soon. And then I took another look at a long-standing annoyance in our OpenVPN network.

I set up OpenVPN so our offices and laptops could securely access internal resources. This lets me ( Read more... )

Originally published at tolaris.com. You can comment here or there.

I use VirtualBox every day. The satellite world is infested with bad Windows-based management tools that fail to run in Wine. So I often run those apps in a Windows virtual machine, safely sandboxed the way Windows belongs.

Note to hardware developers: if your network-based device ( Read more... )