In several places in this memo, specific algorithms that a router ought to follow are specified. These algorithms are not, per se, required of the router. A router need not implement each algorithm as it is written in this document. Rather, an implementation must present a behavior to the external world that is the same as a strict, literal, implementation of the specified algorithm.
Algorithms are described in a manner that differs from the way a good implementor would implement them. For expository purposes, a style that emphasizes conciseness, clarity, and independence from implementation details has been chosen. A good implementor will choose algorithms and implementation methods that produce the same results as these algorithms, but may be more efficient or less general.
We note that the art of efficient router implementation is outside the scope of this memo.