Implementations
No specific hardware or software implementation is required by the protocols or the layered model, so there are many. Most computer operating systems in use today, including all consumer-targeted systems, include a TCP/IP implementation.
A minimally acceptable implementation includes the following protocols, listed from most essential to least essential: IP, ARP, ICMP, UDP, TCP and sometimes IGMP. In principle, it is possible to support only one transport protocol, such as UDP, but this is rarely done, because it limits usage of the whole implementation. IPv6, beyond its own version of ARP (NDP), ICMP (ICMPv6) and IGMP (IGMPv6), has some additional required functions, and often is accompanied by an integrated IPSec security layer. Other protocols could be easily added later (possibly being implemented entirely in userspace), such as DNS for resolving domain names to IP addresses, or DHCP for automatically configuring network interfaces.
Normally, application programmers are concerned only with interfaces in the application layer and often also in the transport layer, while the layers below are services provided by the TCP/IP stack in the operating system. Most IP implementations are accessible to programmers through sockets and APIs.
Unique implementations include Lightweight TCP/IP, an open source stack designed for embedded systems, and KA9Q NOS, a stack and associated protocols for amateur packet radio systems and personal computers connected via serial lines.
Microcontroller firmware in the network adapter typically handles link issues, supported by driver software in the operational system. Non-programmable analog and digital electronics are normally in charge of the physical components below the link layer, typically using an application-specific integrated circuit (ASIC) chipset for each network interface or other physical standard. High-performance routers are to a large extent based on fast non-programmable digital electronics, carrying out link level switching.
Read more about this topic: Internet Protocol Suite