The “J Tree”

In the case of route lookup, the goal is to quickly find the longest match for some prefix, with the corresponding next hop being the information that is sought. The Juniper Networks implementation of a binary tree is called the J-Tree, and it forms the basis of both route lookup and policy-based route filtering.

The above picture shows a binary to powers of a decimal chart, to help with understanding the structure of the J-Tree. For example, the binary sequence 0100 000 equates to a decimal 64, whereas 0110 0000 codes a decimal 96. In this example, bit 8, which has the decimal power of 128, represents the second set of nodes from the top of the tree. The top of the tree represents no bit, and the first pair of nodes down represents a test of the MSB, which is bit 8 in this example, as either 0 (0), or 1 (128).

Once you grasp the J tree all is clear!



~ by bigevil on September 26, 2011.

%d bloggers like this: