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The TCP/IP Guide  9  TCP/IP Lower-Layer (Interface, Internet and Transport) Protocols (OSI Layers 2, 3 and 4)       9  TCP/IP Internet Layer (OSI Network Layer) Protocols            9  Internet Protocol (IP/IPv4, IPng/IPv6) and IP-Related Protocols (IP NAT, IPSec, Mobile IP)                 9  Internet Protocol Version 4 (IP, IPv4)                      9  IP Datagram Delivery and Routing

IP Routing Concepts and the Process of Next-Hop Routing 1 2 3 IP Routing In A Subnet Or Classless Addressing (CIDR) Environment

Route Determination

Now, imagine that this process is expanded to handle thousands of networks and routers. Not only do routers need to know which of their local connections to use for each network, they want to know, if possible, what is the best connection to use for each network. Since routers are interconnected in a mesh there are usually multiple routes between any two devices, but we want to take the best route whenever we can. This may be the shortest route, the least congested, or the route considered optimal based on other criteria.

Determining what routes we should use for different networks turns out to be an important but very complex job. Routers must plan routes and exchange information about routes and networks, which can be done in a variety of ways. This is accomplished in IP using special IP routing protocols. It is through these protocols that R2 and R3 would find out that 14.0.0.0/8 exists and that it is connected to them via R1. I discuss these important “support protocols” in their own section.

IP Routing Concepts and the Process of Next-Hop Routing 1 2 3 IP Routing In A Subnet Or Classless Addressing (CIDR) Environment