his block, corresponding to the numerically lowest of the former Class B addresses, was initially and is still reserved by the IANA. Given the present classless nature of the IP address space, the basis for the reservation no longer applies and addresses in this block are subject to future allocation to a Regional Internet Registry for assignment in the normal manner. Similarly, the 127.0.0.0/8 network should never be used when designing IP networks. Though many people are familiar with the fact that 127.0.0.1 is a local loopback address, many are unaware that the entire network is reserved. RFC 3330 explains: 127.0.0.0/8 - This block is assigned for use as the Internet host loopback address. A datagram sent by a higher level protocol to an address anywhere within this block should loop back inside the host. This is ordinarily implemented using only 127.0.0.1/32 for loopback, but no addresses within this block should ever appear on any network anywhere [RFC1700, page 5]. Public Versus Private IP Space Many companies design their IP networks with a complete disregard for the rules, often using IP ranges that correspond to addresses, building numbers, or branch numbers. The risks of such designs have to do with connectivity and the rules of routing. If a host on the improperly numbered network 15.1.1.1/24 tries to get to a web page on a server with the same IP network and mask, the rules of routing will indicate that they are on the same network, SO the packet will never be forwarded to the default gateway. Some would argue that a firewall with NAT is the solution for poor IP design, but because the host will never forward the packets to the default gateway, they will never be NATed. Additionally, when companies form partnerships with other companies, they often link their networks together. A smart company will not link with a company that vio- lates the IP rules, as they too will be affected since they will inherit routes to the improperly used IP spaces. Remember, if there is a route in the routing table for a d