Alright, let’s talk about the one thing every auditor asks about and most vendors pretend is magic: network segmentation. Specifically, isolating those ancient, terrifyingly vulnerable POS terminals that somehow still run a critical part of the business.
We’ve got a Firebox T40-W running the show. WatchGuard’s marketing makes VLANs sound like a checkbox feature, and in a sense, they’re right—it’s not *technically* hard. The devil, as always, is in the policy sprawl and making sure your “trusted” internal traffic doesn’t decide to go visiting the PCI zone for fun.
Here’s the gist of what actually worked, after untangling the default “Any-Trusted” policies that basically render segmentation pointless.
First, I created a new VLAN (let’s call it VLAN 30) and assigned a dedicated interface on the Firebox. The POS systems get static DHCP leases based on MAC address in this subnet. The key step everyone forgets? On the Firebox, I created an **Alias** for the POS VLAN’s entire subnet. Makes writing policies much cleaner later.
Then, the real work: gutting the default policies. I removed “Any-Trusted” from all relevant rules. Created a new policy that only allows *specific* traffic FROM the POS VLAN TO the payment processor’s IPs on port whatever-they-use, and explicitly DENY anything else trying to egress. Another policy allows limited management traffic FROM our admin VLAN TO the POS VLAN, but with deep inspection turned on. Everything else is logged and dropped.
The satisfying part? Watching the logs fill with blocked attempts from the POS VLAN trying to talk to internal file shares and random internet IPs. Told you they were chatty.
It’s not rocket science, but it requires a mindset shift from “firewall as a wall” to “firewall as a bouncer with a very specific guest list.” And turning off the marketing defaults that assume internal means safe.
—IR
Trust but verify – especially the audit log.
Glad you caught the "Any-Trusted" policy trap. That's where most of these "secure" configurations fall apart before they even start. Vendors ship defaults designed for connectivity, not security, and then wonder why audits fail.
You mentioned using an alias for the subnet - smart move. But how often are you reviewing that alias? Static DHCP is fine until Finance "temporarily" plugs a contractor's laptop into the POS switch for a "quick report." Now that new device is in your nice, clean alias. MAC-based filtering at the switch port level is the tedious, unsexy next step nobody wants to do.
Trust but verify.
That static alias review is a great point. We automate it. A cron job dumps the DHCP lease table daily, compares it against our known MAC/device list, and triggers a ticket if anything new appears. It's not perfect, but it moves the review from "scheduled task we skip" to "alarm bell."
But you're right, MAC filtering is the real control. The pushback is always operational overhead. My counter is that if your change management can't handle updating a switch port config for a new terminal, you've got bigger problems than VLAN design. The MAC list becomes your definitive inventory, and the audit trail in your switch configs is far more reliable than any spreadsheet.
—davidr
That's a solid foundation. When you created the new policy allowing only specific traffic from other networks into the POS VLAN, did you have to whitelist specific IPs for things like central logging servers or patch management? I'm always curious how people handle those required administrative connections without leaving the door too wide open.