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:

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

Routing Protocol Types

Protocol	Characteristics	Examples
Distance Vector	Uses hop count; views the network from its neighbors’ perspective; frequnt updates; copies its routing table to neighbors	RIP, IPX RIP, IGRP
Link State	Shortest path; common view of network; event-triggered update; LSPs (link state packets) sent to all network routers	NLSP, OSPF, IS-IS
Hybrid	Distance vector with more accurate metrics; no periodic updates; only event-triggered	IS-IS, EIGRP

IPX is a member of the IPX/SPX proprietary suite of protocols. IPX operates at the Network layer. It is connectionless and uses datagrams.

NetWare terms to memorize:

Service Advertisement Protocol (SAP) – the NetWare propocol used to advertise (update) the services available over the network.

Routing Information Protocol (RIP) – A distance vector routing protocol similar to RIP in TCP/IP that uses ticks, hop counts and split horizon metrics.

NetWare Link Services Protocol (NLSP) – A link state routing protocol that is the default routing protocol on NetWare 4.11 and higher.

Novell Directory Service (NDS) – Novell’s Directory Service protocol.

NetWare Core Protocol (NCP) – Providing client-to-server connections and applications.

Configuring the router for use with the Novell NetWare IPX protocfol is a two-setp process:

1. Enabling IPX routing: This is done in global configuration mode. You may also enable load sharing if you want.
2. Assigning networks to interfaces: This step in the process assigns network numbers to each interface. Remember that multiple network numbers can be assigned as long as each uses a different encapsulation (frame) type. To apply an encapsulation type, you need to use a Cisco keyword and not the Novell frame type’s name.

Novell IPX Frame Types and Cisco Keywords:

Interface	Novell Frame Type	Cisco Keyword
Ethernet	Ethernet_802.3	novell-ether (default)
Ethernet_802.2		sap
Ethernet_II		arpa
Ethernet_SNAP		snap
Token Ring	Token-Ring	sap (default)
FDDI	Fddi_snap	snap (default)

Tags: 7 layers of the network, packet layer, packet layers, newtwork layers, network layers, network layer diagram, network layer, ccna layer 3, layer 3 network address, layer 3 network

Related posts:

1. The Physical Layer- Layer 1