RIP in Relation to OSI Layers

[3t-sharif]

Just want to clarify the position of RIP on OSI Model.

Why is RIP shown in App layer 7 in the some documents (when showing that it used UDP port 520). Where as it is listed as a L3 protocol in others.

Is it because RIP spans, L 3 to L7.

Becuase it is carried by UDP I think it spans over L3-7 ?

Agree, any thoughts?

Thanks,

[mheusinger]

Hi,

from an IP point of view RIP is an application utilizing transport over IP/UDP.

So this justifies to say it is Layer7. In fact the TCP/IP protocol stack does not implement dedicated Layers 5-7 but only considers anything above Layer4 as "application layer". The OSI model is a reference model used to compare different implementations of network protocol suites. Thus not necessarily all the OSI layers will show up in any given protocol suite.

RIP as an application will announce OSI layer3 reachability information. Personally I would not consider it to be a layer3 protocol. IP is layer3 and nothing else in TCP/IP.

Regards, Martin

[blatkinson]

RIP uses UDP for transport. BGP uses TCP. Some protocols provide their own transport and you can think of them as collapsed down into Layer 3 where the functionality of transport isn't defined up in Layer 4 as in the case of UDP and TCP providing the function of transport. OSPF, IGRP, and EIGRP are commonly classified as layer 3. ARP and ICMP also are layer 3.

[Richard Burts]

Tariq

I personally believe that attempts to clarify position within the OSI model of things like RIP are doomed to inconclusive results. As you analyze it from different aspects you will get different answers. Since RIP uses UDP (port 520) one analysis would indocate that it is a session layer protocol since session (layer 5) is transported over transport/UDP (layer 4).

But analysis from another aspect will note that RIP does not have characteristics of a session layer protocol (it does not coordinate transfer of information between applications on stations at each end of the connection).

And analysis from another aspect will note that RIP processes information about network connectivity and in that aspect it qualifies as an application.

And analysis from another aspect will note (as Martin points out) that OSI might not be the most appropriate model - the TCP/IP model is perhaps more appropriate. And in the TCP/IP model things above the transport layer are applications.

As Martin points out the reference model gives us a way of thinking about how things are organized. But it is frequently difficult to put real life into the reference model.

HTH

Rick