ing to one of many publicly available route servers. To illustrate this point, here's a sample of the number of routes the AT&T IP Services Route Monitor shows as of this writing: route-server>sho ip bgp summary BGP router identifier 12.0.1.28, local AS number 65000 BGP table version is 75630579, main routing table version 75630579 324578 network entries using 39273938 bytes of memory 5975892 path entries using 310746384 bytes of memory 362530/55439 BGP path/bestpath attribute entries using 50754200 bytes of memory 76457 BGP AS-PATH entries using 1996260 bytes of memory 156 BGP community entries using 3744 bytes of memory 0 BGP route-map cache entries using 0 bytes of memory 0 BGP filter-list cache entries using 0 bytes of memory BGP using 402774526 total bytes of memory Dampening enabled. 1280 history paths, 1747 dampened paths BGP activity 1828537/1503956 prefixes, 50259731/44283836 paths, scan interval 60 secs When I wrote the first edition of this book, there were 182,347 network entries on this route server. Roughly four years later, there are 324,578. It is reasonable to assume that any router connected to the Internet that is receiving full tables will contain a similar number of network entries. Notice the fourth line: 324578 network entries using 39273938 bytes of memory Those entries are taking up 39,273,938 bytes of memory in the router versus only 18,417,047 bytes four years ago. More importantly, anytime a change is made to the paths to any of these networks, the entire world of BGP-connected routers must be notified. CIDR comes into play on the Internet because it helps to make these massive tables smaller. It also helps smaller networks (and, more importantly, their administrators) by making local routing tables smaller. Smaller routing tables are more logical, easier to understand, and much simpler to troubleshoot during outages. Allocating IP Network Space One of the problems I've seen repeatedly over the years is improper allocation of IP network space. Whether the trouble is the use of public I