Is Your BGP Up to Snuff?

Routing best practices change and evolve as we collectively gain experience, and this is nowhere more true than with the Internet itself. Because of the vast and growing economic and cultural dependency on the Internet, that ultimate “network of networks” is subject to a level of scrutiny and analysis far beyond what any mere enterprise network undergoes. There are a tremendous number of amazingly intelligent, diligent, committed people striving to make the Internet better.

Because of these efforts, BGP best practices change faster than those of other routing protocols. If you aren’t paying attention, you can get left behind.

Take, for example, route flap damping. At the turn of the century it was accepted wisdom that damping was a good thing (RIPE-229). Misbehaving prefixes accrued penalties, and with enough penalties the prefix was suppressed for a certain amount of time. Most people understood that this contributed to BGP stability by preventing update churn caused by perhaps thousands of prefixes being withdrawn and then re-advertised in various parts of the world.

Then in 2002 a new study demonstrated that, surprisingly, this understanding was wrong and in fact damping causes more instability than it prevents: A flap causes upstream routers to select and advertise next-best routes, which are seen as prefix attribute changes, which in turn accrue their own penalties, which can cause the newly advertised paths to be suppressed. The effect can cascade throughout the Internet’s default-free zone. So where route flap damping was once best practice it is now discouraged (RIPE-378).

Although this advised change has been around for more than a year, a great many network operators are unaware of it.

Conducting a best-practice review of your BGP policies every couple of years is a great way to not only insure that you are up to date, but also serves as a “spring cleaning” exercise to tidy up your policy configurations.