Recovery from control plane failures in the LDP signalling protocol

The Label Distribution Protocol (LDP) needs to recover its state information after a control plane failure, so that the established connections in the data plane are not disrupted by any new connection set-up. We propose a backup mechanism to store the LDP state information in an upstream neighbour node. The backup LDP state information is synchronized with the original LDP state information in a downstream node when the LDP sets up or tears down connections. Then, we propose a two-step LDP state information recovery, which uses a fast LDP state information recovery to recover what labels are idle before a control plane failure, and a detailed LDP state information recovery to fully recover all LDP state information. The fast LDP state information recovery is realized as part of the LDP initialization, allowing a restarting LDP session to process new connection set-up requests as soon as possible, without interfering existing connections. The detailed LDP state information recovery performs in the background in parallel to the normal LDP operations. When an LDP connection teardown requires the LDP state information that has not yet been recovered, an on-demand query based LDP state information recovery is conducted. The performance analysis demonstrates that our proposal achieves fast LDP recovery for the core label state information. It features scalable LDP state information storage and recovery by only involving a pair of neighbour nodes.