ng Figure 15-4 shows an example of a binary tree as it might be viewed for fast switch- ing. Each branch of the tree appends a 0 or a 1 to the previous level's value. Starting at 0 (the root), the next branch to the right contains a 0 on the bottom, and a 1 on the top. Each of those nodes again branches, appending a 0 on the bottom branch, and a 1 on the top branch. Eight levels of the tree are shown in Figure 15-4, but an actual tree used for IP addresses would have 32 levels, corresponding to the bits within an IP address. Dec: 170.x.x.x Bin: 10101010.x.x.x Bits: Figure 15-4. Fast-switching binary tree The nodes marked in gray in Figure 15-4 match an IP address of 170.x.x.x. (The binary value of 170 is 10101010-this should make the example easier to visualize.) The IP address is only 170.x.x.x because the beyond eight bits I couldn't fit any more visible nodes in the drawing. The benefit of this design is speed when compared with searching the RIB. Informa- tion regarding the next hop and MAC address changes is stored within each node. Since the tree is very deterministic, finding specific entries is very quick. The drawbacks of this implementation include the sheer size of the table, and the fact that while the data for each address is stored within the nodes, the size of the data is not static. Because each node may be a different size, the table can be inefficient. Chapter 15: Switching Algorithms in Cisco Routers The route cache is not directly related to the routing table, and it is updated only when packets are process-switched. In other words, the route cache is updated only when the first packet to a destination is switched. From that point, the route cache is used, and the remaining packets are fast-switched. To keep the data in the route cache current, 1/20th of the entire route cache is aged out (discarded) every minute. This information must be rebuilt using process switching. Because the ARP table is not directly related to the contents of the route cache, changes to the ARP table result in parts o