BROCADE IP PRIMER

BI4XGBI4XGBI24CBI24CBI24C16T X RX T X RX T X RX T X RXT X RX T X RX T X RX T X RX12BigIron RX-8NETWORKS7131819242530313637424348AC OK DC OK ALMEJECT SYS AC OK DC OK ALMEJECT SYS AC OK DC OK ALMEJECT SYS AC OK DC OK ALMBI24CBI24CBI24CBI24CBI24CBI4XGBI4XGT X RX T X RX T X RX T X RXT X RX T X RX T X RX T X RXEJECT SYSBI4XGBI4XGBI24CBI24CBI24C16T X RX T X RX T X RX T X RXT X RX T X RX T X RX T X RX12BigIron RX-8NETWORKS7131819242530313637424348AC OK DC OK ALMEJECT SYS AC OK DC OK ALMEJECT SYS AC OK DC OK ALMEJECT SYS AC OK DC OK ALMBI24CBI24CBI24CBI24CBI24CBI4XGBI4XGT X RX T X RX T X RX T X RXT X RX T X RX T X RX T X RXEJECT SYSChapter 2: TCP/IPCIDR notation can also be used to indicate a specific host's subnet mask.Remember our two-host network? The CIDR notation is 192.168.100.0/30.The specific hosts can be represented this way: 192.168.100.1/30 and192.168.100.2/30. This not only indicates their specific address, but it alsotells us what their subnet mask is.RouterRouterT14.0.0.1/8200.0.0.1/30200.0.0.2/305.0.0.1/84.0.0.0/85.0.0.0/8As there is a subnet, there is also such thing as a supernet. This just allowsyou to group multiple addresses together, using CIDR notation. For example,let's say you're using 172.16.0.0/24, 172.16.1.0/24, 172.16.2.0/24, and172.16.3.0/24. Instead of individually referring to all four networks, you couldsimply refer to 172.16.0.0/22. You would not have assigned this as a subnetmask to hosts. It is purely used to refer to large groups of networks. Supernetsare not restricted to the minimum subnet mask length. For example, if Iwanted to represent 8.0.0.0/8, 9.0.0.0/8, 10.0.0.0/8, and 11.0.0.0/8, I couldrefer to the group as 8.0.0.0/6. Notice that the “6” is shorter than the minimumsubnet length of a Class A (“8”). This is okay, as the “6” is not really asubnet mask length, but a mask length to summarize all of the subnets withinthe range. This will come into play more when we starting talking about routingprotocols in Section III.Private Networks (RFC 1918)With classless networking, the Internet could grow and grow, but what aboutorganizations that may want to use TCP/IP, but may not want to use the Internet?For example, a business may have 500 workstations that their employeesuse to communicate locally (e.g., to file servers, internal servers, each other,etc.). If the business wanted to use TCP/IP for its network, it would have to registera network range with its proper registry for Internet numbers (seeChapter 13) in order for each workstation to have an IP address. Also, onceaddressed, each workstation could be accessible from anywhere on the Internet.This may not be desirable, if you have sensitive information on some ofyour servers or workstations.The Internet Engineering Task Force (IETF) publishes a set of standards calledRequest for Comments (RFC). These detail all kinds of different standards forthe Internet. Among them is RFC 1918: Address Allocation for Private Internets.This addresses (no pun intended) the problem by allowing privatenetworks to be created. You can still use TCP/IP, but you don't have to worryabout registering addresses with an Internet registry.52 Brocade IP Primer