Author Archives: Dan Siemon

Internet Redundancy, Or Not

Imagine you are a business that wants to have redundant connections to the Internet. Given the importance of an active Internet connection for many businesses this is a reasonable thing for an IT shop or business owner to ask for. One could also consider the serious home gamer who can’t risk being cut off as another use case.

Let’s dig into the technical options for achieving Internet redundancy.

The first and most obvious path would be to purchase a router that has two WAN ports and ordering Internet service from two different providers. Bam, you are ready to go right? Well… not really.

The way this typically works is that the router will choose one of the two Internet connections for a given outbound connection. The policy could be always use connection A until it fails or be more dynamic and take some advantage of both connections at the same time. The problem with this approach is that because the traffic will be NATed towards each Internet provider, there is no way to fail a given connection from one Internet provider to another. So the failure of one of the Internet connections means that your voice call, SQL or game connection will die, probably after some annoyingly lengthy TCP or application level timeout expires. If the site is strictly doing short outbound connections such as the case with HTTP 1.1 traffic this isn’t such a big deal.

So the ‘get two standard Internet connections and a dual port WAN router’ approach sort of works. Let’s call it partially redundant.

How do we get to true redundancy that can survive a connection failure without dropping connections? To this we need the site’s network to be reachable through multiple paths. The standard way to do this is to obtain IP address space from one of the service providers or get provider independent IP space from one of the registries (such as ARIN). Given that IPv4 addresses are in short supply this isn’t a trivial task. The conditions that have to be met to get address space are well out of the reach of small and medium businesses. Even when the barriers can be met, it’s still archaic to have to do a bunch of paper work with a third party for something that is so obviously needed.

The real kicker is that the lack of IP space is only part of the problem. IPv6’s huge 128-bit address space doesn’t really help at all because to use both paths, the site or home’s IP prefix needs to exist in the global routing table. That is, every core router on the Internet needs an entry that tells it how to reach this newly announced chunk of address space. The specialized memory (CAM) used by these routers isn’t cheap so there is a strong incentive within the Internet operations community to keep this kind of redundancy out of the reach of everyone except other ISPs and large businesses.

So the simple option doesn’t really solve the problem and ‘true’ redundancy isn’t possible for most businesses. What about something over the top?

Consider a router that is connected to multiple standard Internet connections. It could maintain two tunnels, one over each connection, towards another router somewhere else on the Internet. To the rest of the Internet, this second router is where the business is connected to the Internet. If one of the site’s Internet connections fails, the routers can simply continue passing packets over the remaining live tunnel thereby maintaining connectivity to the end site. From an end user’s perspective, this solution mostly works but let’s think about the downsides. We’ve essentially made our site’s redundancy dependent on the tunnel termination router and its Internet connectivity whereas without this we are just at the mercy of the ISP’s network. Also, unless the end site obtains its own address space, this approach has all downsides of the first approach except the NAT related problems occur at the tunnel termination router instead of being on-site. Finally, if the site can get its own address space, why do the tunnel approach at all?

I should note, because someone will point it out in the comments, that for very large organizations it’s possible to get layer two connectivity to each site and essentially build their own internal internet. If they have enough public IP space they can achieve redundancy to the end site for connections with hosts on the public Internet. With private IP space, they can achieve redundancy for connections within their own network. Without public IP space, even these networks suffer from the NAT related failure modes.

To summarize, if you aren’t a very large business, there is no way to get true Internet connection redundancy with the current Internet protocols. That’s kinda sad.

Part 2: Redundant Connections to a Single Host

Part 3: Detecting Failure

RINA

One of my favourite networking books is Patterns in Network Architecture. Unlike most networking books, this one treats networking like a science instead of just explaining how the Internet protocols work.

An interview with the author, John Day, was recently published which covers some of the topics in the book at a very high level. It’s worth a read and so is the book.

And if you have time, dig into RINA. RINA is the network architecture that is built up in the book. There are several academic groups around the world working on this.

Ad Blocking Cat and Mouse Game

There is a little war going on between web ad companies and ad blocking software. For examples of ad blocking software see AdBlock and Firefox’s new tracking protection. The latter focuses on blocking tracking software some of which is ads. I don’t use AdBlock but I do have Firefox’s tracking protection enabled.

One of the reasons ad blocking software works is that ads are typically served from an ad network, not directly from the website the user is visiting.  Specifically, the browser makes a separate connection to a different host to get the ad content. This makes ads easy to distinguish an ad from the rest of the site’s content.

I wonder how long the ad blocking cat and mouse game will go on before the sites that are most reliant on ads simply switch to proxying the ad content through their website. This would add some cost to running the site but it would make it much more difficult to identify which parts of the site are real content and which parts are ads.

Firefox Tracking Protection

So here’s something new I learned today… Firefox has a tracking protection mode.

For those not aware, many (most?) websites include tracking Javascript which provides third parties and the website owner with information about you. It’s not all evil but it does invade your privacy.
Tracking Protection for Firefox at Web 2.0 Security and Privacy 2015
With tracking protection enabled Firefox will block known trackers and has the nice side effect of providing a major browsing speed up.

For a while I’ve configured Firefox to disable third-party cookies. I think it’s time to add enabling tracking protection to my list of new installation steps.

It’s important for the web that no single browser ever gets to the dominance that IE once had. Firefox dethroned IE but now Chrome is becoming dominant. It’s doubtful Chrome would ever implement privacy protecting feature like this – it hurts Google’s primary advertising business too much. If you care about the web and your privacy, consider using Firefox. A healthy number of Firefox users keeps the rest of the web browsers honest.