Conflicting Definitions 2

[Skittle]

I find that different texts give different definitions on things within the Net+ subjects.

Example.

In Cramsession, ARP is listed as OSI level 3 but at this
web site its listed as Level 2. Which is right???

http://compnetworking.about.com/library/glossary/bldef-arp.htm

Dazed and confused

 

[glister]

NETWORK LAYER of the OSI

Address Resolution Protocol is used to map OSI level 3 IP addreses to OSI level 2 MAC addreses. A router has a table of currently used ARP entries. Normally the table is built dynamically, but to increase network security, it can be built statically by means of adding static entries.

Different layer 2 and 3 protocol suites use different methods to perform this mapping, but the most popular is Address Resolution Protocol (ARP). A broadcast "Hello" protocol enables network devices to learn the MAC addresses of other network devices on the same local area network. These mappings are stored in a table, or "cache" called the ARP cache.

Address Resolution Protocol (ARP) is the method used in the TCP/IP suite. When a network device needs to send data to another device on the same network, it knows the source and destination network addresses for the data transfer. It must somehow map the destination address to a MAC address before forwarding the data. First, the sending station will check its ARP table to see if it has already discovered this destination station's MAC address.

Why can't network interfaces simply learn their own IP address and eliminate the need for this mapping? In principle, they could, but this would need specially designed interfaces which could not be used with other protocols. This has not been the strategy of interface manufacturers. Today, there is little doubt that IP is here to stay -- but this has not always been the case. Alternative LAN technologies like ATM looked, at one point, as though they would challenge the Ethernet/IP alliance. The advantage of keeping layer 2 and layer 3 addresses separate is partly historical, and partly practical.

What about the other way around? Couldn't the IP address contain the MAC address? This is not practical in IPv4, since the IP address is shorter than the MAC address. However, in IPv6, MAC addresses are indeed embedded in the IPv6 addresses, using a standard algorithm, thus eliminating the need for ARP and also the need to set IP addresses manually, or with DHCP.

NETWORK OSI LEVEL 3

This layer converts the segments from the Transport layer into packets (or datagrams) and is responsible for path determination, routing, and the delivery of these individual packets across multiple networks without guaranteed delivery. The network layer treats these packets independently, without recognizing any relationship between those packets, it relies on upper layers for reliable delivery and sequencing.
Also this layer is is responsible for logical addressing (also known as network addressing or Layer 3 addressing) for example IP addresses
Examples of protocols defined at this layer: IP, IPX, AppleTalk, ICMP, RIP, OSPF, BGP, IGRP, EIGRP, NLSP, ARP, RARP, X.25
Devices that operate on this layer: Routers, Layer 3 Switches.

http://www.geocities.com/SiliconValley/Monitor/3131/ne/osimodel.html

http://www.how2pass.com/CCNA/study_material/osilayers.htm

http://sabertech.net/routergod/ccnabootcamp/osi.html

http://libra.unitbv.ro/internet/OSI model.htm

http://www.campusprogram.com/reference/en/wikipedia/i/in/internet_protocol_suite.html

A+,N+,S+,L+,I+,HTI+,e-Biz+,CETsr,CST,CNST,CNCT,CFOT,CCNT,CCTT,ACSP,ISA CCST3

 

[jtb]

Glister your answers positively SHINE!!!

JTB
Have Certs, Will Travel
"A knight without armour in a [cyber] land."