IP routing and IP forwarding are two processes that are at the very foundation of the Internet. Every system with TCP/IP protocol installed has at least one network interface called loopback. Besides, it can have one or more network interface cards installed. Let us imagine we have received one link frame, carrying an IP datagram, through the first installed network interface card. Its processing, summarized in Figure 7.1, can be described in the following steps:
- The IP datagram is extracted from the link frame. The sender’s link address can be used to refresh the ARP cache.
- The extracted IP datagram is inserted into an input queue and waits here for its processing.
- Processing of the header options is the first step within the processing. First, the options ‘Loose source routing’ and ‘Strict source routing’ are processed. If the IP datagram belongs (according to the content of the source routing options) to another receiver,...