12.1 Name two key data structures used in the networking subsystem that are important in ensuring that the socket-layer software is kept independent of the networking implementation.
12.2 What work is done by the lower half of a network device driver? What work is done by the upper half of a network device driver?
12.3 Which routines in the protocol switch are called by the socket layer? Explain why each of these routines is called.
12.4 Assume that a reliably-delivered-message socket (SOCK_RDM) is a connectionless socket that guarantees reliable delivery of data and that preserves message boundaries. Which flags would a protocol that supported this type of socket have set in the pr_flags field of its protocol-switch entry?
12.5 Give an example of a network interface that is useful without an underlying hardware device.
12.6 Give two reasons why the addresses of a network interface are not in the network-interface data structure.
12.7 Why is the name or address of a socket kept at the network layer rather than at the socket layer?
12.8 Why does FreeBSD not attempt to enforce a rigid protocol-protocol interface structure?
12.9 Describe two tasks performed by a network-interface output routine.
12.10 Why is the identity of the network interface on which each message is received passed upward with the message?
12.11 Which routing policies are implemented in the kernel?
12.12 Describe three types of routes that can be found in the routing table that differ by the type of destination to which they apply.
12.13 What routing facility is designed mainly to support workstations?
12.14 What is a routing redirect? For what is it used?
12.15 Why do the output-packet queues for each network interface have limits on the number of packets that may be queued?
12.16 What does the SO_OOBINLINE socket option do? Why does it exist?
*12.17 Explain why it is impossible to use the raw socket interface to support parallel protocol implementations some in the kernel and some in user mode. What modifications to the system would be necessary to support this facility?
*12.18 Previous versions of the system used a hashed routing lookup for a destination as a host or as a network. Name two ways in which the radix search algorithm in FreeBSD is more capable.
