Another way to look at it is via the layer definitions themselves. Layer 3 provides logical addressing. In other words an address that is independent of physical hardware containing some mechanism to provide a network and host portion thereby enabling it to be routed. Arp does not do that.
Layer 2 provides physical addressing as well as services to communicate with higher layers (i.e. layer 3). That is a better fit for arp. There are many examples of protocols that do not fit perfectly by definition into a single layer and you can make that arguement for arp at layer 2, however, as discussed above it is certainly not a layer 3 protocol. So in my eyes that debate is null and void due to the absence of any other suitable contenders. Hope that helps, Andres On 13/12/2011 7:31 PM, "CCIE KID" <[email protected]> wrote: Hey guys, I guess they say its a Layer 2 or Layer 3 on the basis of encapsulation. ARP is encapsulated in Layer 2 header. So its a Layer 2 protocol But OSPF, EIGRP and ICMP are encapsulated in Layer 3. So thats why it is a Layer 3 Protocol. So on the basis of encapsulation, they would have brought out that the protocol is a Layer 2 or Layer 3. BGP,RIP are encapsulated in TCP and UDP respectively. So they are application layer protocol. Where does it encapsulate depends upon where it sits in OSI Layer, ARP sits above Layer 2 but layer 3. So thats why Scott would have called it as a Layer 2.5 Protocol OSPF,ICMP,EIGRP are all payloads of IP . They are all present above IP but below Layer 4. So they r all Layer 3.5 protocol. So it all depends upon where does the protocol actually sits in the OSI layer. I guess this topic would have opened up many logics in networking I thank everyone who contributed I also enjoy working on this topic On Tue, Dec 13, 2011 at 1:55 PM, Michael Davis - Webquor < [email protected]> wrote: > Sorry... _______________________________________________ For more information regarding industry leading CCIE Lab training, please visit www.ipexpert.com Are you a CCNP or CCIE and looking for a job? Check out www.PlatinumPlacement.com http://onlinestudylist.com/mailman/listinfo/ccie_rs
