ed entries in its forwarding table for each unique IP address. The size of the Internet routing table today is in the high hundreds of thousands. Once AT&T completed the migration of the core to MPLS, the Internet routing table was removed from the core routers. The forwarding tables in the core routers was reduced from one with many hundreds of thousands of entries to one that had the size on the order of the number of PEs in the network (thousands). This dramatically reduced the amount of memory and processing that a core router needed to perform and replaced large and complex forwarding tables with much simpler tables that swapped labels. Consider what happens if the link between A and B from the network model shown in Figure 13.12 is lost. The nodes will communicate the link state change to each other using their routing protocol and dynamically shift the flow of traffic bypassing the failed link. The LSP connecting PE1 to PE3 now gets routed along the path A-C-D-B and the LSP connecting PE2 to PE3 gets rerouted to go from C-D-B. The new LSP is realized via changes in the forwarding tables of A and C. In short, the network is adaptive and resilient (Figure 13.13). However, there is a catch; it takes time for all of the nodes to receive routing updates indicating the link failure and to recompute their forwarding tables to include the new paths. For example, A is close to the failure and is the first to detect it and update its forwarding tables. It will now forward packets destined for PE3 to C. But until C is informed of the failure and has a chance to update its for- warding table, it will continue to forward packets destined for PE3 to A! This creates what is called a micro-loop-a spiral death dance for packets. There is a field in the header known as time-to-live (TTL) that gets decremented by 1 each time the packet traverses a node. If the field is decremented use Label 17 for PE3 use Label 33 for PE3 use Label 56 for PE3 use Label 8 for PE3 After Convergence, the new rules would be - A would load rule: 