If you don’t normally read IPJ, you should. Melchoir and I have an article up in the latest edition on link state in DC fabrics.
To make a case for linkstate protocols in DC fabric underlays, an extensive examination of the positive and negative aspects of BGP—and the other available protocols—is essential. Ultimately, it is up to individual operators to decide which protocol is “the best” for their application, a decision based on business and operational—as well as technical—reasons.
According to RFC1925, the second fundamental truth of networking is: No matter how hard you push and no matter what the priority, you can’t increase the speed of light.
A recent paper on network control and management (which includes Jennifer Rexford on the author list—anything with Jennifer on the author list is worth reading) proposes a clean slate 4d approach to solving much of the complexity we encounter in modern networks. While the paper is interesting, it’s very unlikely we will ever see a clean slate design like the one described, not least because there will always be differences between what the proper splits are—what should go where.
This week is very busy for me, so rather than writing a single long, post, I’m throwing together some things that have been sitting in my pile to write about for a long while.
From Dalton Sweeny:
A physicist loses half the value of their physics knowledge in just four years whereas an English professor would take over 25 years to lose half the value of the knowledge they had at the beginning of their career. . . Software engineers with a traditional computer science background learn things that never expire with age: data structures, algorithms, compilers, distributed systems, etc. But most of us don’t work with these concepts directly. Abstractions and frameworks are built on top of these well studied ideas so we don’t have to get into the nitty-gritty details on the job (at least most of the time).
The Open Systems Interconnect (OSI) model is the most often taught model of data transmission—although it is not all that useful in terms of describing how modern networks work. What many engineers who have come into network engineering more recently do not know is there was an entire protocol suite that went with the OSI model. Each of the layers within the OSI model, in fact, had multiple protocols specified to fill the functions of that layer. For instance, X.25, while older than the OSI model, was adopted into the OSI suite to provide point-to-point connectivity over some specific kinds of physical circuits. Moving up the stack a little, there were several protocols that provided much the same service as the widely used Internet Protocol (IP).
The RPKI, for those who do not know, ties the origin AS to a prefix using a certificate (the Route Origin Authorization, or ROA) signed by a third party. The third party, in this case, is validating that the AS in the ROA is authorized to advertise the destination prefix in the ROA—if ROA’s were self-signed, the security would be no better than simply advertising the prefix in BGP. Who should be able to sign these ROAs? The assigning authority makes the most sense—the Regional Internet Registries (RIRs), since they (should) know which company owns which set of AS numbers and prefixes.
The general idea makes sense—you should not accept routes from “just anyone,” as they might be advertising the route for any number of reasons. An operator could advertise routes to source spam or phishing emails, or some government agency might advertise a route to redirect traffic, or block access to some web site. But … if you haven’t found the tradeoffs, you haven’t looked hard enough. Security, in particular, is replete with tradeoffs.
The word on the street is that everyone—especially network engineers—must learn to code. A conversation with a friend and an article passing through my RSS reader brought this to mind once again—so once more into the breach. Part of the problem here is that we seem to have a knack for asking the wrong question. When we look at network engineer skill sets, we often think about the ability to configure a protocol or set of features, and then the ability to quickly troubleshoot those protocols or features using a set of commands or techniques.
According to RFC1925, the first fundamental truth of networking is: it has to work. While this might seem to be overly simplistic, it has proven—over the years—to be much more difficult to implement in real life than it looks like in a slide deck. Those with extensive experience with failures, however, can often make a better guess at what is possible to make work than those without such experience. The good news, however, is the experience of failure can be shared, especially through self-deprecating humor.
According to Maor Rudick, in a recent post over at Cloud Native, programming is 10% writing code and 90% understanding why it doesn’t work. This expresses the art of deploying network protocols, security, or anything that needs thought about where and how. I’m not just talking about the configuration, either—why was this filter deployed here rather than there? Why was this BGP community used rather than that one? Why was this aggregation range used rather than some other? Even in a fully automated world, the saying holds true.
In the argument between OSPF and BGP in the data center fabric over at Justin’s blog, I am decidedly in the camp of IS-IS. Rather than lay my reasons out here, however (a topic for another blog post?), I want to focus on something else Justin said that I think is incredibly important for network engineers to understand.
I think whiteboards are the most important tool for network design currently available, which makes me sad. I wish that wasn’t true, I want much better tools. I can’t even tell you the number of disasters averted by 2-3 great network engineers arguing over a whiteboard.