Explain TCP/IP network interfaces

The TCP/IP Network Interface layer formats IP datagrams at the Network layer into packets that specific network technologies can understand and transmit.

A network interface is the network-specific software that communicates with the network-specific device driver and the IP layer in order to provide the IP layer with a consistent interface to all network adapters that might be present.

The IP layer selects the appropriate network interface based on the destination address of the packet to be transmitted. Each network interface has a network address. The Network Interface layer is responsible for adding or removing any link layer protocol header required to deliver a message to its destination. The network adapter device driver controls the network adapter card.

Although not required, a network interface is usually associated with a network adapter. For instance, the loopback interface has no network adapter associated with it. A machine must have one network adapter card for each network (not network type) to which it connects. However, a machine requires only one copy of the network interface software for each network adapter it uses. For instance, if a host attaches to two token-ring networks, it must have two network adapter cards. However, only one copy of the token-ring network interface software and one copy of the token-ring device driver is required.

TCP/IP supports types of network interfaces:

• 
  Standard Ethernet Version 2 (en)

• 
  IEEE 802.3 (et)

• 
  Token-ring (tr)

• 
  Serial Line Internet Protocol (SLIP)

• 
  Loopback (lo)

• 
  FDDI

• 
  Serial Optical (so)

• 
  Point-to-Point Protocol (PPP)

• 
  Virtual IP Address (vi)

The Ethernet, 802.3, and token-ring interfaces are for use with local area networks (LANs). The SLIP interface is for use with serial connections. The loopback interface is used by a host to send messages back to itself. The Serial Optical interface is for use with optical point-to-point networks using the Serial Optical Link device handler. Point to Point protocol is most often used when connecting to another computer or network via a modem. The Virtual IP Address interface (also called virtual interface) is not associated with any particular network adapter. Multiple instances of a virtual interface can be configured on a host. When virtual interfaces are configured, the address of the first virtual interface becomes the source address unless an application has chosen a different interface. Processes that use a virtual IP address as their source address can send packets through any network interface that provides the best route for that destination. Incoming packets destined for a virtual IP address are delivered to the process regardless of the interface through which they arrive.

• Automatic configuration of network interfaces
  
  
  When a new network adapter is physically installed in the system, the operating system automatically adds the appropriate network interface for that adapter.
  
  
• TCP/IP default configuration values
  
  At each system startup, the operating system automatically configures the network interface software based upon the information in the ODM database. Initially, the network interface is configured with default values.
  
  
• Implications of multiple network interfaces on the same network
  If multiple network interfaces are attached to a single network, each interface must have a unique IP address.
  
  
• Network interface management
  To manage network interfaces, use the WSM Network, FastPath (application) or the tasks in this table.
  
  
• Interface-specific network options
  TCP/IP interfaces must be specially tuned to achieve good, high-speed network performance (100 Mb or more). This effort is complicated by the fact that multiple network interfaces and a combination of traditional and high-speed TCP/IP interfaces can be used on a single system.