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Category Archives for "Russ White"

DNS Cookies and DDoS Attacks

DDoS attacks, particularly for ransom—essentially, “give me some bitcoin, or we’ll attack your server(s) and bring you down,” seem to be on the rise. While ransom attacks rarely actually materialize, the threat of DDoS overall is very large, and very large scale. Financial institutions, content providers, and others regularly consume tens of gigabits of attack traffic in the normal course of operation. What can be done about stopping, or at least slowing down, these attacks?

To answer, this question, we need to start with some better idea of some of the common mechanisms used to build a DDoS attack. It’s often not effective to simply take over a bunch of computers and send traffic from them at full speed; the users, and the user’s providers, will often notice machine sending large amounts of traffic in this way. Instead, what the attacker needs is some sort of public server that can (and will) act as an amplifier. Sending this intermediate server should cause the server to send an order of a magnitude more traffic towards the attack target. Ideally, the server, or set of servers, will have almost unlimited bandwidth, and bandwidth utilization characteristics that will make the attack appear Continue reading

No Capes, No Wands

As a keen observer of the network engineering world for the last twenty… okay, maybe longer, but I don’t want to sound like an old man telling stories quite yet… years, there’s one thing I’ve always found kind-of strange. We have a strong tendency towards hero worship.

I don’t really know why this might be, but I’ve seen it in Cisco TAC—the almost hushed tones around a senior engineer who “is brilliant.” I’ve seen it while sitting in a meeting in the middle of an argument over some technical point in a particular RFC. Someone says, “we should just ask the author…” Which is almost always followed by something like: “Really? You know them?”

To some degree, this is understandable—network engineering is difficult, and we should truly honor those in our world who have made a huge impact. In many other ways, it’s unhelpful, and even unhealthy. Why?

First, it tends to create an “us versus them,” atmosphere in our world. There are engineers who work on “normal” networks, and then there are those who work on, well, you know, special ones. Not everyone needs those “special skills,” so we end up creating a vast pool of people Continue reading

When prepend fails, what next? (3)

We began this short series with a simple problem—what do you do if your inbound traffic across two Internet facing links is imbalanced? In other words, how do you do BGP load balancing? The first post looked at problems with AS Path prepend, while the second looked at de-aggregating and using communities to modify the local preference within the upstream provider’s network.

There is one specific solution I want to discuss a bit more before I end this little series: de-aggregation. Advertising longer prefixes is the “big hammer” of routing; you should always be careful when advertising more specifics. The Default Free Zone (DFZ) is much like the “commons” of an old village. No-one actually “owns” the routing table in the global Internet, but everyone benefits from it. De-aggregating don’t really cost you anything, but it does cost everyone else something. It’s easy enough to inject another route into the routing table, but remember the longer prefix you inject shows up everywhere in the world. You’re fixing your problem by taking up some small amount of memory in every router that’s connected to the DFZ in the world. If everyone de-aggregates, everyone has to buy larger routers and more Continue reading

Reading List: 060916

A few of the papers, RFCs, and drafts I’m reading this week, along with a short description of each.

A Survey of Worldwide Censorship Techniques
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Censorship is a large problem on the Internet—but it’s often difficult to find any good description of the various ways censors can both find and block “offending” content. This draft is a short, readable overview of the various techniques actually seen in the wild, along with pointers to research about the techniques themselves, and instances where they’ve been used in the real world.

IPv6 Extension Headers and Packet Drops
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One of the interesting features of IPv6 is its support for extension headers, which are variable length bits of information—metadata about the packet, for instance—that can be attached to a packet and processed by either the receiving host or forwarding devices along the way. Extension headers are useful, in that they allow IPv6 to be easily extended on the fly, rather than forcing the protocol designer to create a set of metadata “in stone.” Extension headers, however, are also controversial; how should an ASIC designer decide which ones to support in hardware, and how should extension headers that cannot be handled in hardware Continue reading