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Understanding Protocols

This section includes:

Understanding TCP/IP Protocols

Cisco TCP/IP Suite adheres to networking protocols that ensure reliable delivery of information from one host to another.

This section describes the main protocols used by Cisco TCP/IP Suite:

Understanding the Internet Protocol (IP)

The Internet Protocol (IP) is the networking protocol used to deliver packets of information from one computer to another. The computers may reside on different networks as long as information can travel between their networks.

IP is responsible for:

Understanding the Transmission Control Protocol (TCP)

The Transmission Control Protocol (TCP) provides a reliable mechanism for delivery of information to remote hosts. It receives the information to be delivered from the application and initiates a connection with the remote host for delivery of the information.

On the sending host, TCP is responsible for:

On the receiving host, TCP is responsible for:

TCP requires more overhead than UDP but provides reliable delivery of packets to the target host.

Understanding the User Datagram Protocol (UDP)

Applications can also use the User Datagram Protocol (UDP) to deliver information to a target host.

UDP is responsible for:

UDP does not verify the successful delivery of packets to the target host. As a result, UDP requires less overhead than TCP. To accommodate this lack of verification, applications that use UDP should provide their own mechanisms for ensuring that messages reach the target host in the correct sequence.

An advantage of UDP is that it is a connectionless protocol. If a user mounts a drive using NFS and the NFS server goes down, load balancing can be used to connect to a secondary NFS server without the user being aware of the change.

Understanding the Serial Line Internet Protocol (SLIP)

The Serial Line Internet Protocol (SLIP) allows the transmission of IP packets over serial lines. SLIP can be used over a direct connection between the serial ports of two systems, or over telephone lines with modems.

Understanding the Point-to-Point Protocol (PPP)

Like SLIP, the Point-to-Point Protocol (PPP) allows the transmission of IP packets over serial lines. PPP is a more versatile protocol than SLIP, and contains functionality that SLIP does not, such as:

While PPP is a more versatile serial-line protocol than SLIP, it is not available with all TCP/IP implementations.

Understanding Dynamic Configuration Protocols

To communicate with the rest of the network, a host must have an IP address. However, some systems do not have the hardware to permanently store an IP address. In addition, computers frequently share IP addresses when there are more computers than IP addresses, or when IP addresses are used only temporarily. For these situations, Cisco TCP/IP Suite supports two dynamic configuration protocols: BOOTP and DHCP.

Understanding the Bootstrap Protocol (BOOTP)

BOOTP (Bootstrap Protocol) lets a host receive an IP address and the location of a configuration file from a BOOTP server on the network. The host then downloads the configuration file, which contains the information necessary for it to communicate on the network. BOOTP lets systems that have no hard disk retrieve the minimal information necessary to configure their TCP/IP stacks.

Understanding the Dynamic Host Configuration Protocol (DHCP)

The Dynamic Host Configuration Protocol (DHCP) is a superset of the BOOTP protocol. A host receives all of the information necessary to function as a host on the network directly from a DHCP server. Unlike BOOTP, which only provides permanent IP addresses, DHCP supports three mechanisms for allocating IP addresses:

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