Tag Archives: Layer 3

The Network Layer – Layer 3

The Network layer of the OSI Model basically defines logical addressing and the ways that packets are moved from source to destination on a network. The functions of the Network layer can be broken down as follows:

The Network Layer Layer 3 246x300 The Network Layer   Layer 3

  • Message addressing
  • Path determination between source and destination nodes on different networks
  • Routing messages between networks
  • Controlling congestion on the subnet
  • Translating logical addresses into physical addresses
  • Logical Address Construction

    Protocol Total Address Length Bits in Network Portion Bits in Host Portion
    TCP/IP 32 Class A – 8
    Class B – 16
    Class C – 24
    Class A – 24
    Class B – 16
    Class C – 8
    IPX 80 32 or less (only
    significant digits listed)
    48 bits (MAC address)
    AppleTalk 24 16 or less (indicates one
    or many in cable range)
    8 bits or less
    (cynamically assigned)

    Routing protocols support routed protocols. A routing protocol is used to pass messages between routers for maintaining and updating routing tables. Examples of routing protocols are RIP, IGRP, OSPF, EIGRP.
    Routed protocols are used to carry end-user traffic across the internetwork. Examples of routed protocols are IP and IPX Read more »