Understanding and Mitigating the Effects of Count to Infinity in Ethernet Networks

Ethernet's high performance, low cost, and ubiquity have made it the dominant networking technology for many application domains. Unfortunately, its distributed forwarding topology computation protocol-the rapid spanning tree protocol (RSTP)-is known to suffer from a classic count-to-infinity problem. However, the cause and implications of this problem are neither documented nor understood. This paper has three main contributions. First, we identify the exact conditions under which the count-to-infinity problem manifests itself, and we characterize its effect on forwarding topology convergence. Second, we have discovered that a forwarding loop can form during count to infinity, and we provide a detailed explanation. Third, we propose a simple and effective solution called RSTP with Epochs. This solution guarantees that the forwarding topology converges in at most one round-trip time across the network and eliminates the possibility of a count-to-infinity induced forwarding loop.