if you receive a packet with label 56, swap the label to 17 and send packet on interface to C B would load rule: if you receive a packet with label 8, remove (pop) the label and send packet on interface to PE3 C would load rule: if you receive a packet with label 17, swap the label to 33 and send packet on interface to D D would load rule: if you receive a packet with label 33, swap the label to 8 and send packets on interface to B FIGURE 13.13 Network state after a link failure with basic LDP. Building the Network of the Future use Label 17 for PE3 use Label 33 for PE3 use Label 56 for PE3 use Label 8 for PE3 After link A-B fails but before the network converges, a routing loop exists between A and C - A would load rule: if you receive a packet with label 56, swap the label to 17 and send packet on interface to C (new rule) B would load rule: if you receive a packet with label 8, remove (pop) the label and send packet on interface to PE3 C would load rule: if you receive a packet with label 17, swap the label to 56 and send packet on interface to A (old rule) D would load rule: if you receive a packet with label 33, swap the label to 8 and send packets on interface to B FIGURE 13.14 Micro-loop exists after failure but before network fully converges. to zero, the packet is dropped. The process of updating all nodes in the network with new routing and forwarding information in response to a state change is known as "convergence" (Figure 13.14). The time to convergence follows a stochastic distribution. There are many parameters to con- sider-what is the diameter of the network, how big are the routing and forwarding tables, and what other activities are happening in the network that are competing for CPU resources on the route processors. Most flows converge in a matter of seconds but the tail of the distribution could extend out tens of seconds for the outliers. 13.2.2.2 Fast Reroute and Hitless Rearrangements These micro-loops can be avoided by the use of a protocol called Resource Reservation Protocol (RSVP) [1