Why is the Feasibility Condition Less Than?
A reader recently emailed me with this question: Why isn’t the condition for a Feasible Successor set to less than (B. D will immediately reroute to the FS, which is C, without changing the FC. This works, because C’s cost to 100::/64 via D is 4, much higher than it’s cost to 100::64 along C->A.…
OSPF Topology Transparent Zones
Anyone who has worked with OSPF for any length of time has at least heard of areas—but perhaps before diving into Topology Transparent Zones (TTZs), a short review is in order. In this diagram, routers A and B are in area 0, routers C and D are Area Border Routers (ABRs), and routers E, F,…
The EIGRP SIA Incident: Positive Feedback Failure in the Wild
Reading a paper to build a research post from (yes, I’ll write about the paper in question in a later post!) jogged my memory about an old case that perfectly illustrated the concept of a positive feedback loop leading to a failure. We describe positive feedback loops in Computer Networking Problems and Solutions, and in…
What’s wrong with the IETF. And what’s right
I have not counted the IETF’s I have attended; I only know the first RFC on which I’m listed as a co-author was published in 2000, so this must be close to 20 years of interacting with the IETF community. I’m pretty certain I’ve attended at least two meetings a year in some years, and…
DFS and Low Points
On a recent history of networking episode, Alia talked a little about Maximally Redundant Trees (MRTs), and the concept of Depth First Search (DFS) numbering, along with the idea of a low point. While low points are quickly explained in my new book in the context of MRTs, I thought it worthwhile to revisit the…
SLAAC and DHCPv6
When deploying IPv6, one of the fundamental questions the network engineer needs to ask is: DHCPv6, or SLAAC? As the argument between these two has reached almost political dimensions, perhaps a quick look at the positive and negative attributes of each solution are. Originally, the idea was that IPv6 addresses would be created using stateless…
If you haven’t found the tradeoff…
This week, I ran into an interesting article over at Free Code Camp about design tradeoffs. I’ll wait for a moment if you want to go read the entire article to get the context of the piece… But this is the quote I’m most interested in: [time-span] Just like how every action has an equal…
Leave Your Ego at the Door
You are just about to walk into the interview room. Regardless of whether you are being interviewed, or interviewing—what are you thinking about? Are you thinking about winning? Are you thinking about whining? Or are you thinking about engaging? I have noticed, on many mailing lists, and in many other forums, that interviews in our…
Securing BGP: A Case Study (10)
The next proposed (and actually already partially operational) system on our list is the Router Public Key Infrastructure (RPKI) system, which is described in RFC7115 (and a host of additional drafts and RFCs). The RPKI systems is focused on solving a single solution: validating that the originating AS is authorized to originate a particular prefix.…
Securing BGP: A Case Study (9)
There are a number of systems that have been proposed to validate (or secure) the path in BGP. To finish off this series on BGP as a case study, I only want to look at three of them. At some point in the future, I will probably write a couple of posts on what actually…