TCP/IP (Overview)
This chapter introduces the Solaris implementation of the TCP/IP network protocol suite. The information is intended for network administrators who are unfamiliar with TCP/IP. If you are an experienced TCP/IP network administrator, consider reading chapters that cover the tasks that you want to perform.
This chapter contains the following information:
Introducing the Internet Protocol Suite
This section presents an in-depth introduction to the protocols that compose TCP/IP. Although the information is conceptual, you should learn the names of the protocols and what each does.
TCP/IP is the abbreviation that is commonly used for the set of network protocols that compose the Internet Protocol suite. Many texts use the term "Internet" to describe both the protocol suite and the global wide area network. In this book, the "TCP/IP" refers specifically to the Internet protocol suite. "Internet" refers to the wide area network and the bodies that govern the Internet.
To interconnect your TCP/IP network with other networks, you must obtain a unique IP network number. At the time of this writing, the InterNIC organization assigns IP network numbers.
If hosts on your network are to participate in the Internet domain name system (DNS), you must obtain and register a unique domain name. The InterNIC also handles the registration of domain names under certain top-level domains such as .com (commercial), .edu (education), and .gov (government). Chapter 3, Planning Your TCP/IP Network (Task) contains more information about the InterNIC. For more information on DNS, refer to System Administration Guide: Naming and Directory Services (DNS, NIS, and LDAP).
Protocol Layers and the OSI Model
Most network protocol suites are structured as a series of layers, sometimes referred to collectively as a protocol stack. Each layer is designed for a specific purpose. Each layer exists on both the sending and receiving hosts. A specific layer on one machine sends or receives exactly the same object that another machine's peer process sends or receives. These activities occur independently from activities in layers above or below the layer under consideration. Effectively, each layer on a host acts independently of other layers on the same machine. Each layer acts in parallel with the same layer on other hosts.
OSI Reference Model
Most network protocol suites are viewed as structured in layers. The International Organization for Standardization (ISO) designed the Open Systems Interconnection (OSI) Reference Model that uses structured layers. The OSI model describes a structure with seven layers for network activities. Each layer associates one or more protocols with the layer. The layers represent data transfer operations common to all types of data transfers among cooperating networks.
The OSI Reference Model lists the protocol layers from the top (layer 7) to the bottom (layer 1). The following table shows the model.
Table 2-1 Open Systems Interconnection Reference Model
Layer No. | Layer Name | Description |
|---|---|---|
7 | Consists of standard communication services and applications that everyone can use. | |
6 | Ensures that information is delivered to the receiving machine in a form that the machine can understand. | |
5 | Manages the connections and terminations between cooperating computers. | |
4 | Manages the transfer of data. Also assures that the received data are identical to the transmitted data. | |
3 | Manages data addressing and delivery between networks. | |
2 | Handles the transfer of data across the network media. | |
1 | Defines the characteristics of the network hardware. |
The OSI model defines conceptual operations that are not unique to any particular network protocol suite. For example, the OSI network protocol suite implements all seven layers of the OSI Reference Model. TCP/IP uses some of OSI model layers. TCP/IP also combines other layers. Other network protocols, such as SNA, add an eighth layer.
TCP/IP Protocol Architecture Model
The OSI model describes an idealized network communications with a family of protocols. TCP/IP does not correspond to this model directly. TCP/IP either combines several OSI layers into a single layer, or does not use certain layers at all. The following table shows the layers of the Solaris implementation of TCP/IP. The table lists the layers from the topmost layer (application) to the lowest (physical network).
Table 2-2 TCP/IP Protocol Stack
OSI Ref. Layer No. | OSI Layer Equivalent | TCP/IP Layer | TCP/IP Protocol Examples |
|---|---|---|---|
5,6,7 | Application, session, presentation | NFS, NIS+, DNS, telnet, ftp, rlogin, rsh, rcp, RIP, RDISC, SNMP, and others | |
4 | Transport | TCP, UDP | |
3 | Network | IP, ARP, ICMP | |
2 | Data link | PPP, IEEE 802.2 | |
1 | Physical | Ethernet (IEEE 802.3) Token Ring, RS-232, others |
The table shows the TCP/IP protocol layers. Also shown are the OSI Model equivalents with examples of the protocols that are available at each level of the TCP/IP protocol stack. Each host that is involved in a communication transaction runs a unique implementation of the protocol stack.
Physical Network Layer
The physical network layer specifies the characteristics of the hardware to be used for the network. For example, physical network layer specifies the physical characteristics of the communications media. The physical layer of TCP/IP describes hardware standards such as IEEE 802.3, the specification for Ethernet network media, and RS-232, the specification for standard pin connectors.
Data-Link Layer
The data-link layer identifies the network protocol type of the packet, in this instance TCP/IP. The data-link layer also provides error control and "framing." Examples of data-link layer protocols are Ethernet IEEE 802.2 framing and Point-to-Point Protocol (PPP) framing.
Internet Layer
This layer, also known as the network layer, accepts and delivers packets for the network. This layer includes the powerful Internet Protocol (IP), the Address Resolution Protocol (ARP), and the Internet Control Message Protocol (ICMP).
IP Protocol
The IP protocol and its associated routing protocols are possibly the most significant of the entire TCP/IP suite. IP is responsible for the following:
IP addressing - The IP addressing conventions are part of the IP protocol. Chapter 3, Planning Your TCP/IP Network (Task) describes IPv4 addressing in detail and Chapter 14, IPv6 (Overview) describes IPv6 addressing in detail.
Host-to-host communications - IP determines the path a packet must take, based on the receiving host's IP address.
Packet formatting - IP assembles packets into units that are known as IP datagrams. Datagrams are fully described in "Internet Layer".
Fragmentation - If a packet is too large for transmission over the network media, IP on the sending host breaks the packet into smaller fragments. IP on the receiving host then reconstructs the fragments into the original packet.
Previous releases of the Solaris operating environment implement version 4 of the Internet Protocol, which is abbreviated as IPv4. However, because of the rapid growth of the Internet, a new Internet Protocol was created. The new protocol increases address space. This new version, known as version 6, is abbreviated as IPv6. The Solaris operating environment supports both versions, which are described in this book. To avoid confusion when addressing the Internet Protocol, one of the following conventions is used:
When the term IP is used in a description, the description applies to both IPv4 and IPv6.
When the term IPv4 is used in a description, the description applies only to IPv4.
When the term IPv6 is used in a description, the description applies only to IPv6.
ARP Protocol
The Address Resolution Protocol (ARP) conceptually exists between the data-link and Internet layers. ARP assists IP in directing datagrams to the appropriate receiving host by mapping Ethernet addresses (48 bits long) to known IP addresses (32 bits long).
ICMP Protocol
Internet Control Message Protocol (ICMP) detects and reports network error conditions. ICMP reports on the following:
Dropped packets - Packets that arrive too fast to be processed
Connectivity failure - A destination host that cannot be reached)
Redirection - Redirecting a sending host to use another router
The "ping Command" contains more information on the operating system commands that use ICMP for error detection.