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Solaris TCPIP Protocol Suite (Overview)
This chapter introduces the Solaris implementation of the TCP/IP network protocol suite. The information is intended for system and network administrators who are unfamiliar with basic TCP/IP concepts. The remaining parts of this book assume that you are familiar with these concepts.
This chapter contains the following information:
Introducing the TCP/IP Protocol Suite
This section presents an in-depth introduction to the protocols that are included in TCP/IP. Although the information is conceptual, you should learn the names of the protocols. You should also learn what each protocol does.
"TCP/IP" is the acronym 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, "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 address for your network. At the time of this writing, you obtain this address from an Internet service provider (ISP).
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 coordinates the registration of domain names through a group of worldwide registries. For more information on DNS, refer to System Administration Guide: Naming and Directory Services (DNS, NIS, and LDAP).
Protocol Layers and the Open Systems Interconnection Model
Most network protocol suites are structured as a series of layers, sometimes collectively referred to as a protocol stack. Each layer is designed for a specific purpose. Each layer exists on both the sending and receiving systems. A specific layer on one system sends or receives exactly the same object that another system's peer process sends or receives. These activities occur independently from activities in layers above or below the layer under consideration. In essence, each layer on a system acts independently of other layers on the same system. Each layer acts in parallel with the same layer on other systems.
OSI Reference Model
Most network protocol suites are 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. One or more protocols is associated with each layer. The layers represent data transfer operations that are common to all types of data transfers among cooperating networks.
The OSI model lists the protocol layers from the top (layer 7) to the bottom (layer 1). The following table shows the model.
Table 1-1 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 system in a form that the system can understand. | |
5 | Manages the connections and terminations between cooperating systems. | |
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 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 idealized network communications with a family of protocols. TCP/IP does not directly correspond to this model. 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 bottommost layer (physical network).
Table 1-2 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, LDAP, telnet, ftp, rlogin, rsh, rcp, RIP, RDISC, SNMP, and others | |
4 | Transport | TCP, UDP, SCTP | |
3 | Network | IPv4, IPv6, ARP, ICMP | |
2 | Data link | PPP, IEEE 802.2 | |
1 | Physical | Ethernet (IEEE 802.3), Token Ring, RS-232, FDDI, and others |
The table shows the TCP/IP protocol layers and the OSI model equivalents. Also shown are examples of the protocols that are available at each level of the TCP/IP protocol stack. Each system 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
The Internet layer, also known as the network layer or IP 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. Designing an IPv4 Addressing Scheme introduces IPv4 addressing and IPv6 Addressing Overview introduces IPv6 addressing.
Host-to-host communications - IP determines the path a packet must take, based on the receiving system's IP address.
Packet formatting - IP assembles packets into units that are known as datagrams. Datagrams are fully described in Internet Layer: Where Packets Are Prepared for Delivery.
Fragmentation - If a packet is too large for transmission over the network media, IP on the sending system breaks the packet into smaller fragments. IP on the receiving system then reconstructs the fragments into the original packet.
The Solaris OS supports both IPv4 and IPv6 addressing formats, 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 system by mapping Ethernet addresses (48 bits long) to known IP addresses (32 bits long).
ICMP Protocol
The 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 system cannot be reached
Redirection - Redirecting a sending system to use another router
Chapter 8, Administering a TCP/IP Network (Tasks) contains more information on the Solaris OS commands that use ICMP for error detection.