We all use the OSI model to describe the way networks work. I have, in fact, included it in just about every presentation, and every book I have written, someplace in the fundamentals of networking. But if you have every looked at the OSI model and had to scratch your head trying to figure out how it really fits with the networks we operate today, or what the OSI model is telling you in terms of troubleshooting, design, or operation—you are not alone. Lots of people have scratched their heads about the OSI model, trying to understand how it fits with modern networking. There is a reason this is so difficult to figure out.
The OSI Model does not accurately describe networks.
What set me off in this particular direction this week is an article over at Errata Security:
The OSI Model was created by international standards organization for an alternative internet that was too complicated to ever work, and which never worked, and which never came to pass. Sure, when they created the OSI Model, the Internet layered model already existed, so they made sure to include today’s Internet as part of their model. But the focus and intent of the OSI’s efforts was on dumb networking concepts that worked differently from the Internet.
When a recursive resolver receives a query from a host, it will first consult any local cache to discover if it has the information required to resolve the query. If it does not, it will begin with the rightmost section of the domain name, the Top Level Domain (TLD), moving left through each section of the Fully Qualified Domain Name (FQDN), in order to find an IP address to return to the host, as shown in the diagram below.
This is pretty simple at its most basic level, of course—virtually every network engineer in the world understands this process (and if you don’t, you should enroll in my How the Internet Really Works webinar the next time it is offered!). The question almost no-one ever asks, however, is: what, precisely, is the recursive server sending to the root, TLD, and authoritative servers?
YANG is a data modeling language used to model configuration data, state data, Remote Procedure Calls, and notifications for network management protocols, described in RFC7950. The origins of YANG are rooted in work Phil Shafer did in building an interface system for JUNOS. Phil joins us on this episode of the History of Networking to discuss the history of YANG.
The Internet, and networking protocols more broadly, were grounded in a few simple principles. For instance, there is the end-to-end principle, which argues the network should be a simple fat pipe that does not modify data in transit. Many of these principles have tradeoffs—if you haven’t found the tradeoffs, you haven’t looked hard enough—and not looking for them can result in massive failures at the network and protocol level.
Another principle networking is grounded in is the Robustness Principle, which states: “Be liberal in what you accept, and conservative in what you send.” In protocol design and implementation, this means you should accept the widest range of inputs possible without negative consequences. A recent draft, however, challenges the robustness principle—draft-iab-protocol-maintenance.
According to the authors, the basic premise of the robustness principle lies in the problem of updating older software for new features or fixes at the scale of an Internet sized network. The general idea is a protocol designer can set aside some “reserved bits,” using them in a later version of the protocol, and not worry about older implementations misinterpreting them—new meanings of old reserved bits will be silently ignored. In a world where even a very old operating system, such as Windows XP, is still widely used, and people complain endlessly about forced updates, it seems like the robustness principle is on solid ground in this regard.
I recently spoke at CHINOG on the business value of disaggregation, and participated in a panel on getting involved in the IETF.
Multicast is, at best, difficult to deploy in large scale networks—PIM sparse and BIDIR are both complex, adding large amounts of state to intermediate devices. In the worst case, there is no apparent way to deploy any existing version of PIM, such as large-scale spine and leaf networks (variations on the venerable Clos fabric). BEIR,…
The BGP specification suggests implementations should have three tables: the adj-rib-in, the loc-rib, and the adj-rib-out. The first of these three tables should contain the routes (NLRIs and attributes) transmitted by each of the speaker’s peers. The second table should contain the calculated best paths; these are the routes that will be (or are) installed…
When rolling out a new protocol such as IPv6, it is useful to consider the changes to security posture, particularly the network’s attack surface. While protocol security discussions are widely available, there is often not “one place” where you can go to get information about potential attacks, references to research about those attacks, potential counters,…