Internetworking Notes

Introduction

Internetworks allow for the creation of scalable networks that can manage heterogeneity, overcoming limitations often faced by LAN switches. The Internet Protocol (IP) serves as the core mechanism for connecting different networks, enabling them to act as a cohesive internetwork.

Service Model

The IP service model consists of two primary components:

  1. Addressing Scheme: Identifies all hosts in the internetwork.

  2. Datagram Delivery: A connectionless service model labeled as "best effort," which means there are no guarantees of delivery.

Datagram Delivery – Packet Format

  • The maximum size of an IP datagram is 65,53565,535 bytes, dependent on the underlying network's support.

  • The TTL (Time to Live) field, set typically to 6464, prevents packets from circulating indefinitely.

  • Each packet includes SourceAddr and DestinationAddr for addressing, as well as a checksum for error detection.

Fragmentation and Reassembly

When a datagram exceeds the network's Maximum Transmission Unit (MTU), fragmentation occurs. Each fragment contains an identifier for reassembly at the destination. For example, Ethernet permits 15001500 byte packets, while a point-to-point network may only support 532532 bytes.

Address Translation (ARP)

The Address Resolution Protocol (ARP) is used to translate IP addresses to link-layer addresses required for network transmission. Each host maintains a dynamic ARP table that maps IP addresses to physical addresses, updating periodically to ensure accuracy.

Host Configuration (DHCP)

DHCP automates the assignment of IP addresses to hosts, reducing manual errors and labor. When a host connects, it sends a DHCPDISCOVER, and DHCP servers respond with address assignments.

Error Reporting (ICMP)

ICMP is designed to report errors in datagram handling, such as unreachable hosts or dwell time expiration (TTL reaching zero). It is integral for tools like ping and traceroute, and provides feedback to source hosts about routing issues.