Graceful Restart
No doubt you have experienced some sort of routing meltdown in your networking career. Unfortunately, it is a fact that failures are inevitable, whether software or hardware or a combination of the two. The challenge is to make them as painless as possible.
Let’s take a simple routing process failure as an example, in which a routing daemon restarts on one of the core routers. The restart causes a networkwide disruption to many of the network processes and brings down all protocol adjacencies. While the router is recovering, all its neighbors shift their traffic in different directions, using redundant links or paths. It is possible that the shifted traffic, now on oversubscribed links, causes congestion and potential traffic drops. When the failed router recovers, it establishes new adjacencies and advertises new routing information, which in turn causes another traffic shift back to the original paths. This is actually how basic routing handles failures; according to the protocol definitions, each step in this scenario happened as it was designed to. But how does this situation affect the users?
The traffic churn has substantial impact on the user experience. This is especially true with the content being delivered using modern next-generation networks, which consist primarily of video and voice communication, in which any delay and jitter can cause havoc. If you have seen a distorted or frozen picture on your cable TV, it was likely caused by jitter. Moreover, ...