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Review of IP Addressing, Routing protocols and Subnet masks

Depending on the routing protocols used, you can specify IP addresses based on: 1) Network Classes (A,B,C) with an associated classful default subnet mask. 2) Classes with variable length, subnet masks (VLSM) , 3) (CIDR) Classless Inter-Domain Routing with a specified prefix length

The Class B default subnet mask is 255.255.0.0. Another way to characterize the default Class B subnet mask is to use the classless notation or 'slash' notation. In the case of the default Class B subnet mask, 255.255.0.0 can be represented as /16. This means that the first 16 bits of the IP address represent the network ID.

Class-based networks support a single subnet mask, and are suitable for networks routed by using Routing Information Protocol (RIP) 1.0 VLSM and CIDR support multiple masks or prefixes per network. Both VLSM and CIDR require routers that support more advanced interior routing protocols, such as RIP 2.0 and (OSPF) Open Shortest Path First.

Class based IP addresses are split into two portions, 1) network ID and 2) host ID. The subnet mask is used to define which portion of the IP address defines the network ID. The remaineder of the IP address is dedicated to the host ID. The Internet Protocol uses the network ID portion of the subnet mask to determine whether a destination host is local or remote.