TCAM characteristics. Since the power dissipation of a TCAM is approximately proportional to the number of cells (see Chapter 5), it is important to devise schemes to reduce the number of entries in the TCAM SO to adopt lower power circuits. A first algorithm of this type, very simple, but nevertheless quite effective, is based on the elimination of redundant prefixes. Let us imagine that 1000110 has only one child 10001100 and both are associated to the same output port address. It is clear that, imagining the prefixes trie, the second prefix can be eliminated, attaching all its children directly under the first. This situation is quite common in a great number of forwarding tables of core and edge routers; thus, even sim- ply eliminating redundant nodes in the prefixes trie helps a lot in reducing the number of prefixes to be loaded into the TCAM. The second technique exploits TCAM hardware's flexibility. The mask for a routing prefix stored in TCAM consists of ones (the same number of ones as the prefix length) followed by all zeros. However, TCAM allows the use of an arbitrary mask, SO that the bits of ones or zeros needn't be continuous. This technique is called mask extension because it extends the mask to be any arbitrary combination of ones and zeros. A simple example helps to describe the mask extension technique. Let us assume that the two prefixes 10010011 and 10000011 both correspond to the same route, port A. It's possible to combine the two prefixes into a single entry, with the prefix set to 100X0011, associated to the port A. Using both the aforementioned techniques a typical forwarding table can be reduced eliminating 35% or even 45% of the prefixes SO to proportionally gain in dissipated power. Last, but not least, TCAMs have to be updated hundreds of times per second. Most rout- ing updates are route flaps-the same prefix is added and then removed repeatedly in quick succession. It is straightforward to reduce the number of actual updates by keeping a buffer of recent route update announcements