What is a Distributed Firewall?
In the post “What is Network Virtualization?” I described a model where the application’s complete L2-L7 virtual network is decoupled from hardware and moved into a software abstraction layer for the express purpose of automation and business agility. In this post I’ll focus on network security, and describe an imminent firewall form factor enabled by Network Virtualization — the Distributed Firewall.
ALL YOUR PACKET ARE BELONG TO US
If InfoSec ruled the world … well, OK, maybe not the world … if InfoSec ruled the data center network design, and if money was no object, we would probably have something like this. Every server in the data center directly connected to its own port on one massive firewall. Every packet sent from every server would be inspected against a stateful security policy before going anywhere. And every packet received by every server would pass one final policy check before hitting the server’s NIC receive buffer. The firewall wouldn’t care about the IP address of the servers, for the simple reason that it’s directly connected to every server. E.g. “The server on this port can talk to the server on that port, on TCP port X”. And if that wasn’t good enough, the firewall knows everything about the servers connected to it, and can create rules around a rich set of semantics. All of this with no performance penalty. That would be awesome, right?
Let’s pretend money was not the issue. How would you design this massive omnipresent data center firewall? I can think of three ways off hand.
- You design a monstrous power sucking stateful firewall chassis with thousands of line-rate ports. At this point it’s time to route a ghastly mess of cables from every server to this centralized mega firewall core chassis – but that’s somebody else’s problem. Oh, and don’t forget you’ll need two of those bad boys for “redundancy”. Your monster firewall is pretty freaking awesome at security, but only so-so at basic L2 and L3 networking. But so what — the network team can learn to like it or find a new job. And if you run out of ports … no worries; just wait another few years for a bigger chassis and do the rip/replace routine.
- You design a line rate stateful firewall ToR switch. Rip out the network team’s favorite ToR and put this one in its place. Tell them to stop throwing a fit and just deal with it. You’ll have hundreds of these ToR firewalls to manage and configure consistently. No problem … just let the network team re-apply for their jobs as firewall engineers.
Go ahead and pinch yourself now. This is nothing but a fantasy nightmare.
The interests of security often poorly translate into networking. Comprehensive security ~= Compromisednetworking.
What about design #3? More on that in a minute. (Hint: title of the post)
In the real world, rest assured we do have firewalls to provide some security. But this security is not ubiquitous, nor is it assured. Instead, we have firewalls (physical or virtual) hanging off the network somewhere catching steered packets – and we can only hope the network was configured correctly to steer the right traffic to the right policy.
In this post we’ll briefly review the physical and virtual firewall, followed by a discussion on the Distributed Firewall.
When you are experiencing slow Internet access, you may want to test the Internet speed of your upstream ISP (often called « last mile » in the residential broadband networks) as part of troubleshooting. For that matter, 
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