Managing NFS and NIS, 2nd Edition - Mike Eisler [173]
Conversely, the one-filled octets are treated like wildcards and imply "any" host on the network. The network number is specified but the host number matches all hosts on that network. Using these connotations for octet values 0 and 255, the ones form of the broadcast address is "correct." There are cases in which the zeros form must be used for backwards compatibility with older operating system releases. Many systems were built using the zeros form of broadcast addresses.
The sole requirement in adopting a broadcast address form is to make the choice consistent across all machines on the network and compatible with your vendor's supported convention. Machines that expect a zeros-form broadcast address interpret a one-filled octet as part of a host number rather than a wildcard. Mixing broadcast address forms on the same network is the most common cause of broadcast storms, in which every confused node on the network transmits and retransmits replies to a broadcast address of a form complementary to the one it is using.
Broadcast addresses, muticast addresses, IP addresses, and other characteristics of the Ethernet interface are set with the ifconfig utility. Because ifconfig governs the lowest level interface of a node to the network, it is the logical place to begin the discussion of network tools.
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[1] IPv6-aware applications can communicate with nodes that do not have an IPv4 address. This means that the application can handle the larger IPv6 addresses.
[2] IPv6-enabled applications take advantage of some IPv6-specific feature. The enabled applications can still operate over IPv4, though in a degraded mode. IPv6-enabled applications are also IPv6-aware.
[3] IPv6-unaware applications cannot handle IPv6 addresses; therefore, they cannot communicate with nodes that do not have an IPv4 address.
[4] Multicast addresses are used to define subgroups of recipients of data. If a sender needs to contact a large number of hosts simultaneously, the sender can multicast a single message to all hosts listening on the given multicast address, instead of issuing multiple copies of the same message to every single host. The hosts listening on the multicast address do not need to be part of the same subnetwork as the sender.
[5] The 4.2 BSD release of Unix introduced TCP/IP and required use of the zeros form of broadcast addresses. All derivatives of 4.2 BSD, including SunOS 3.x and early versions of Ultrix, retained this broadcast address requirement. In 4.3 BSD, the ones form of broadcast addresses was adopted, although the zeros form was still supported. Unix operating systems that are descendants of 4.3 BSD — SunOS 4.x included — support both one- and zero-filled broadcast addresses. Solaris supports only the ones form.
MAC and IP layer tools
The tools covered in this section operate at the MAC and IP layers of the network protocol stack. Problems that manifest themselves as NFS or NIS failures may be due to an improper host or network configuration problem. The tools described in this section are used to ascertain that the basic network connectivity is sound. Issues that will be covered include setting network addresses, testing connectivity, and burst traffic handling.
ifconfig: interface configuration
ifconfig sets or examines the characteristics of a network interface, such as its IP address or availability. At boot time, ifconfig is used to initialize network interfaces, possibly doing this in stages since some information may be available on the network itself through NIS. You can also use ifconfig to examine the current state of an interface and compare its address assignments with NIS map information. Interfaces may be physical devices, logical devices associated with a physical network interface, IP tunnels, or pseudo-devices such as the