RFC Series (Part 4)
Experience Has Shown That
(RFC2915, Rule 4)
The world of information technology is filled, often to overflowing, with those who “know better.” For instance, I was recently reading an introduction to networking in a very popular orchestration system that began with the declaration that: ‘routing was hard, and therefore this system avoided routing’. The document then went on to describe a system of moving packets around using multiple levels of Network Address Translation (NAT) and centrally configured policy-based routing (or filter-based forwarding) that was clearly simpler than the distributed protocols used to run large-scale networks. I thought, for a moment, of writing the author and pointing out the system in question had merely reinvented routing in a rather inefficient and probably broken way, but I relented. Why? Because I know RFC2915, rule 4, by heart:
Some things in life can never be fully appreciated nor understood unless experienced firsthand.In other words, some things in networking can never be fully understood by someone who neither builds commercial networking equipment nor runs an operational network. Ultimately, the people who built this system will likely not listen to me; rather, they are going to have to experience the pain caused by large-scale failures for themselves.
Many network operators do wish for some way to get their experience across to users and application developers. For example, one suggestion which has been made in the past is adding subliminal messages to the TELNET protocol. According to RFC1097, adding this new message type would allow operators to gently encourage users to upgrade the software they are using by displaying a message on-screen which the user’s mind can process, but is not consciously aware of reading. The uses of such a protocol extension, however, could be wide-ranging, such as informing application developers that the network is not cheap, and packets are not carried instantaneously from one host to another.
A further suggestion made in this direction is to find ways to more fully document operational experience in Internet Standards produced by the Internet Engineering Task Force (IETF). Currently, the standards for writing such standards (sometimes mistakenly called meta-standards, although these standards about standards are standards in their own right) only include a few keywords which authors of protocol standards can use to guide developers into creating well-developed implementations. For instance, according to RFC2119, a protocol designer can use the term MUST (note the uppercase, which means it must be shouted when reading the standard out loud) to indicate something an implementation must do. If the implementation does not do what it MUST, subliminal messaging (as described above) will be used to discourage the use of that implementation.
MUST NOT, SHOULD, SHOULD NOT, MAY, and MAY NOT are the remaining keywords defined by the IETF for use in standards. While these options do cover a number of situations, they do not express the full range of options available based on operational experience. RFC6919 proposed extensions to these keywords to allow a fuller range of intent which could be useful to express experience.
For instance, RFC6919 adds the keyword MUST (BUT WE KNOW YOU WON’T) to express operational frustration for those times when even subliminal messaging will not convince a user or application developer to create an implementation that will gracefully scale. The POSSIBLE keyword is also included to indicate what is possible in the real world, and the REALLY SHOULD NOT is included for those times when an application developer or user asks for the network operator to launch pigs into flight.
Of course, the keywords described in RFC6919 may, at some point, be extended further to include such keywords as EXPERIENCE HAS SHOWN THAT and THAT WILL NOT SCALE, but for now protocol developers and operators are still somewhat restricted in their ability to fully express the experience of operating large-scale networks.
Even with these additional keywords and the use of subliminal messaging, improper implementations will still slip out into the wild, of course.
And what about network operators who are just beginning to learn their craft, or have long experience but somehow still make mistakes in their deployments? Some have suggested in the past—particularly those who work in technical assistance centers—that all network devices be shipped according to the puzzle-box protocol.
Meaning that all network devices should be shipped in puzzle boxes such that only those with an appropriate level of knowledge, experience, and intelligence can open the box and hence, install the equipment. Some might argue the Command Line Interface (CLI) currently supplied with most networking equipment is the equivalent of a puzzle box, but given the state of most networks, it seems shipping network equipment with a complex and difficult-to-use CLI has not been fully effective.
See you next month…