Your instructor is one of the all-too-large group of people who try
to coerce things into a simplistic OSI model. Priscilla calls this
coercing protocols into OSI layers. It's really not the fault of OSI,
because there are documents that supplement the original model, such
as the Rout(e)ing Framework, Internal Organization of the Network
Layer, Management Annex, etc.
The OSI stack principally was drawn to show how standard
communications service user applications, which run on top of the
service interface to the application layer. Management was something
of an afterthought, and what is called system management -- think
SNMP, or the OSI rough equivalent, CMIP -- does indeed involve an
application layer protocol and a management application above it.
Routing, error notification, etc., are considered layer management.
There is nothing "above" them; they are part of the infrastructure
for a given layer. So,all of them are logically layer 3.
The issue of the mechanism they use to transfer information between
them is independent of the layer they manage. In Chuck's table
below, EIGRP and OSPF do have transport functions that are part of
their own design--which have a TCP-like flavor. For that matter, ISIS
runs directly over data link.
>Recently an instructor in a class I was taking said something I found
>interesting. I hope I can do justice to his words.
>
>Network layer: IP IP IP
>Transport layer: TCP UDP
>Application layer: BGP RIP EIGRP, OSPF, IGRP
>
>In other words, he suggested that routing protocols are application layer,
>and use the chosen transport or network layer protocols to communicate.
>Other reading I have done kinda says this in other ways. RIP uses UDP port
>500. BGP, as we all know, uses TCP.
>
>Does this make sense?
>
>Chuck
A post I made yesterday might help:
At 4:16 PM -0500 11/10/2000, Howard C. Berkowitz wrote:
>At 12:22 PM -0800 11/10/2000, Julian Eccli wrote:
>>Does anyone know the definition of Control Plane from a generic
>>routing protocol
>>standpoint? Is it the same definition as in ATM? I have heard references to
>>control planes in various talks but they were not specific to ATM.
>>
>
>Unfortunately, it isn't as well-specified in IP routing as in the
>B-ISDN/ATM architecture. Many IP discussions merge what that
>architecture calls the control and management plane.
>
>Personally, I think merging the two is rather unfortunate. In IP
>networks, I consider control plane protocols those that are used for
>signaling between hosts and ingress/egress routers. Examples: ARP,
>IGMP. Another way to think about them is that they serve a
>user-to-network role.
>
>I consider pure management plane protocols to those used between
>routers: BGP, OSPF, EIGRP, RIP, etc. Arguably, these have a
>network-to-network role.
>
>There are protocols that don't neatly fit, such as RSVP and ICMP. I
>suppose they are control plane when host initiated and management
>plane when router initiated, but that doesn't always work and is
>ugly anyway.
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