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.

Oracle Solaris 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 Oracle Solaris commands that use ICMP for error detection.