ADDRESS AGGREGATION AND SUBNET MASKS AND PREFIXES

Address aggregation is introduced in Chapter 1. It is the method used today to reduce the size of the routing tables. It is quite similar to the use of subnet masks, with the following exceptions: (a) the net and subnet bits are contiguous, and begin in the high-order (most significant) part of the address space, (b) a 32-bit submask is not used, rather (c) a prefix value is appended to the end of an address to describe how many bits are to be used as the mask. In most routers, addresses can be configured with a conventional decimal doted notation, or a prefix.

Figure B-10 shows how address aggregation is used. The three subnets 172.16.1.0, 172.16.2.0, and 172.16.3.0 use a prefix of 24. This value ...

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