François Clad, the loopfree forwarding man

Since September 2011, François Clad joins us to prepare his Ph.D.
Jean-Jacques Pansiot is the director of this Ph.D. thesis and I assist him with Antoine Gallais. Our work is devoted to the improvement of the routing convergence in dynamics networks. In particular, we aim at avoiding transient forwarding loops due to the non controlled order of FIB updates. The field of applications we target is quite large: we are interested by link state wired networks as well as wireless sensors networks where the context and constraints are totally differents.
The complete subject is available here (in french):
Some preliminary slides are also available here (in french):

Fig.1: The routing tree to 1 before the removal of 4-1
Fig.2: The routing tree to 1 after the removal of 4-1

On the small toy network of Fig.1, we provide in red the reverse Shortest Path Tree (rSPT) rooted towards the destination 1. After updating the link weight of edge 4-1, the new rSPT is given in green in Fig.2 : when merging the two rSPT, we can notice that several cycles appear. Those cycles emphasize the potential presence of forwarding loops if the order of the application of Link State Updates (LSU) is not favorable on routers. For example, again towards destination 1, if router 4 updates its FIB before router 3 applies its LSU, a forwarding loop occurs between these two routers.

Our goal is to avoid such transient forwarding loop problems by proposing incremental and practicable solutions in real IP networks. We aim at improving the convergence plan of IP routing protocols.