Chapter 6 – Network Configuration

An interface is any channel through which network data can flow. Hardware network interfaces are defined by physical network connections, while virtual network interfaces are logical network connections that ride on top of hardware network connections.A protocol is a set of rules used to describe a specific type of network communication.

Protocols are necessary for separate network devices to communicate properly. Finally, a network service (as it pertains to the Network preferences) is the collection of settings that define a network connection.

The Internet Protocol (IP) address identifies the location of a specific network device. IP addresses are the primary identification used by the Internet protocol suite TCP/IP for both local area and wide area networks.

Subnet masks are used by network devices to identify their local network range and to determine if outgoing data is destined fora network device on the LAN.

Most common IP addresses and subnet masks share the same IPv4 formatting. An IPv4 address is a 32-bit number represented in four groups of three-digit numbers, known as octets, separated by periods. Each octet has a value between 0 and 255. An IPv6 address is a 128-bit number that is presented in eight groups of four-digit hexadecimalnumbers separated by colons. This allows for a huge range of addresses, and as a result IPv6 addressing essentially includes subnet information.

If a network device needs to send data to another network device on the same LAN, it addresses the outgoing packets based on the destination device's MAC address.

A network client uses the subnet mask to determine if the destination IP address is on the LAN. If the destination IP address is not on the LAN, it's assumed the destination address is on another network, and the client sends the data to the IP address of the local network router. The network router then sends the data, via a WAN connection, on to another router that it thinks is closer to the destination.

This continues across WAN connections from router to router until the data reachesits destination.

The DNS service is used to translate host names to IP addresses via forward lookups and translate IP addresses to host names via reverse lookups. DNS is architected as a hierarchy of worldwide domain servers. Local DNS servers provide name resolution and possibly host names for local clients.

These local DNS servers connect to DNS servers higher in the DNS hierarchy to resolve both unknown host names and host local domain names.

A Service Set Identifier, or SSID, is used to identify a Wi-Fi network name and associated configuration.

OS X supports authenticated Wi-Fi via the following authentication protocols: WEP, WPA/WPA2 Personal, and WPA/WPA2 Enterprise, which includes support for 802.1X authentication.

A new OS X system can only automatically connect to Wi-Fi networks that have no standard authentication mechanism, otherwise known as an "open network." However, a configured OS X system can automatically reconnect to authenticated Wi-Fi networks, provided that the appropriate information was saved to the Keychain system.

A standard user can connect to any non-WPA Enterprise Wi-Fi network via the Wi-Fi status menu. Because the system Keychain must be modified for WPA Enterprise connections, only an administrative user can establish these types of connections.

A network location is a saved state of the Network preferences that contains all network interface settings. Only administrators can define network locations, but if more than one location exists, all users can switch between the various network locations via the Apple menu.

OS X supports the following network interfaces and protocols:• Wired Ethernet IEEE 802.3 family of hardware network interface standards• Wireless (Wi-Fi) IEEE 802.11 family of hardware network interface standards• FireWire IEEE 1394 hardware network interface• Analog modem hardware network interface• Bluetooth wireless hardware network interface• USB connectivity via cellular network adapters• Virtual private network (VPN) virtual network interface via the Point-to-PointTunneling Protocol (PPTP)• VPN virtual network interface via the Layer 2 Tunneling Protocol (L2TP) overInternet Protocol Security (IPSec)• VPN virtual network interface via Cisco IPSec• Point-to-Point Protocol over Ethernet (PPPoE) virtual network interface• 6 to 4 virtual network interface• Virtual local area network (VLAN) virtual network interface via the IEEE 802.1Qstandard• Link Aggregation virtual network interface via the IEEE 802.3ad standard• Transmission Control Protocol/Internet Protocol (TCP/IP), also known as theInternet protocol suite• Dynamic Host Configuration Protocol (DHCP)• Domain Name Service (DNS) protocol• Network Basic Input/Output System (NetBIOS) and Windows Internet NamingService (WINS) protocols• Authenticated Ethernet via the 802.

1X protocol• Point-to-Point Protocol (PPP)

OS X does not support AppleTalk.

The network service order list is used to determine the primary network service interface if there is more than one active service. All network traffic that isn't better handled via local connection to an active network service interface is sent to the primary network service interface. Thus, in most cases all WAN traffic, Internet traffic, and DNS resolution is sent through the primary network service interface.

In the Network preferences, all network service interfaces with a green status indicator are being used for network activities. However, again, all network traffic that isn't better handled via a local connection is sent to the primary network service interface.

The primary network service interface is the topmost active interface in the listing.

The easiest method to configure VPN settings is use a configuration profile containing all the relevant VPN setup information.

On OS X there are two configuration methods for 802.1X.

The first method is automatic configuration via the selection of a Wi-Fi network that requires WPA/WPA2 Enterprise authentication. The second method is "semi-automatic" configuration via an administrator-provided 802.1X configuration profile.

Four common issues that interrupt network services on Macs are:• Ethernet connectivity issues can cause the hardware network interface to becomeinactive or introduce excessive packet errors.• Wi-Fi connectivity issues caused by the selection of an improper Wi-Fi networkor excessive wireless interference.• DHCP service issues prevent proper TCP/IP configuration.

• DNS service issues prevent host name resolution.

If DHCP is specified as the configuration for a TCP/IP connection and no DHCP service is available, the device automatically selects a random IP address in the 169.254. xxx.

xxx range. It checks the local network to ensure that no other network device is using the randomly generated IP address before it applies the IP address. In most cases, though, this addressing is not normal, and it's often indicative of a problem with DHCP services.

You can identify all the MAC addresses for the Mac computer's network interfaces from the Info pane of Network Utility.

The Ping tab of Network Utility allows you to test basic connectivity to another network host by sending and then waiting for the return of a ping packet.

The Lookup tab of Network Utility allows you to test name resolution against the currently configured DNS server.

The Traceroute tab of Network Utility allows you to verify the connection hops between your Mac and a remote host.