Reducing Complexity through Interaction Surfaces

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.

There is one section of the paper that eloquently speaks to current architecture, however. The authors describe a situation where routing and packet filters are used together to prevent one set of hosts from reaching another set of hosts. Changes in the network, however, cause the packet filters to be bypassed, opening up communications between these two sets of hosts.

This is exactly the problem we so often face in network engineering today—overlapping systems used to solve a single problem do not pay attention to the same signals or information to do their jobs. So here’s a thought about an obvious way to reduce the complexity of your network—try to use one tool to do one job. Before the days of automation, this was much harder to do. There was no way to distribute QoS configurations, for instance, or access lists, much less what might be considered an “easy way.” Because of this, it made some kind of sense to use routing protocols as a sort of distributed database and policy engine to move filters and the like around.

Today, however, we have automation. Because of this, it makes more sense to use automation to manage as much data plane policy as you can, leaving the routing protocol to do its job—provide reachability across an ever-changing network. There are still things, like traffic steering and prefix distribution rules, which should stay inside routing. But when you put routing filters in place to solve a data plane problem, it might be worth thinking about whether that is the right thing to do any longer.

Automation, in this case, can change everything.