While those working in the network engineering world are quite familiar with the expression “it is always something!,” defining this (often exasperated) declaration is a little trickier. The wise folks in the IETF, however, have provided a definition in RFC1925. Rule 7, “it is always something,” is quickly followed with a corollary, rule 7a, which says: “Good, Fast, Cheap: Pick any two (you can’t have all three).”
You can either quickly build a network which works well and is therefore expensive, or take your time and build a network that is cheap and still does not work well, or… Well, you get the idea. There are many other instances of these sorts of three-way tradeoffs in the real world, such as the (in)famous CAP theorem, which states a database can be consistent, available, and partitionable (or partitioned). Eventual consistency, and problems from microloops to surprise package deliveries (when you thought you ordered one thing, but another was placed in your cart because of a database inconsistency) have resulted. Another form of this three-way tradeoff is the much less famous, but equally true, state, optimization, surface tradeoff trio in network design.
It is possible, however, to build a system which fails at all three measures—a system which is expensive, takes a long time to build, and does not perform well. The fine folks at the IETF have provided examples of such systems.
For instance, RFC1149 describes a system of transporting IPv4 packets over avian carriers, or pigeons. This is particularly useful in areas where electricity and network cabling are not commonly found. To quote the relevant part of the RFC:
The IP datagram is printed, on a small scroll of paper, in hexadecimal, with each octet separated by whitestuff and blackstuff. The scroll of paper is wrapped around one leg of the avian carrier. A band of duct tape is used to secure the datagram's edges. The bandwidth is limited to the leg length.
The specification of duct tape is quite odd, however; perhaps the its water-resistant properties are required for this mode of transport. This mode of transport has been adapted for use with the more modern (in relative terms only!) IPv6 transport in RFC6214. For situation where quality of service is critical, RFC2549 describes quality of service extensions to the transport mechanism.
To further prove it is possible to build a network which is slow, expensive, and does not work well, RFC4824 describes the transmission of packets through semaphore flag signaling, or SFSS. Commonly used to signal between two ships when no other form of communication is available, SFSS consists of a sender who positions (waves) flags of particular shape and color in specific positions to signal individual characters. Rather than transmitting letters or other characters, RFC4824 describes using these flags to transmit 0’s, 1’s, and the framing elements required to transmit an IPv4 datagram over long distances. The advantage of such a system is, much like the avian carrier, that it will operate where there is no electricity. The disadvantage is the cost of encoding and decoding the packet’s contents may be many orders of magnitude more difficult than using existing SFSS specifications to signal messages.
Finally, RFC7511 provides an option which allows the most use of resources on any network while providing the slowest possible network performance by allowing senders to include a scenic route header on IPv6 packets. This header notifies routers and other networking devices that this packet would like to take the scenic route to its destination, which will cause paths including avian carriers (as described in RFC6214) to be chosen over any other available path.
Russ White has more than twenty years' experience in designing, deploying, breaking, and troubleshooting large scale networks. Russ is currently a member of the Architecture Team at LinkedIn, where he works on next generation data center designs, complexity, and security. His most recent books are The Art of Network Architecture and Navigating Network Complexity.