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  1. Senior Member
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    #51
    Quote Originally Posted by CaySpekko View Post

    Sure the OSPF software running on the router is an application, but it's application is internal to the router, and not used in the network stack layers 4 5 6 or 7.
    This is where I think the key to the debate and confusion may lay. A protocol in and of itself is not necessarily an application, but the implementation of that protocol may be. Trying to apply operational details to a conceptual framework is a good way to generate a headache.
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  3. Senior Member Chris_'s Avatar
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    #52
    I think forsaken has hit the nail on the head. The OSI model is a conceptual framework intended to assist in the demarcation of processes involved in communications. It is always going to be open to interpretation.

    My own opinion is that routing protocols are applications that exist to facilitate the functions of layer 3. In my mind anything that processes and exchanges information that has payloads encapsulated within tcp/udp headers is leaning towards being an application (I know this doesn't apply to OSPF or eigrp but there us still a layer 4 exchange of sorts within the ip encapsulation)
    Please don't attack me
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  4. The whole Shebang! hiddenknight821's Avatar
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    #53
    Quote Originally Posted by MrXpert View Post
    I'm surprised at your answer considering you're a ccent and i am not. is it such a silly debate? then why so many posts about it?
    I personally tend to question things when different sources say different things.Looks like I am not the only one needing to rehit the books as you suggested
    No need to reply here since I apparently just learned from this interesting debate as well as the others that you just refuted. Don't assume CCENT will teach you this. Not even the CCNA made it clear as well. If it wasn't for the experienced CCNP folks here, you would probably still be wrestling around with your friends. Anyway, no one wins in this debate since there is no definite answer yet. So far CaySpekko made so much sense out of this whole discussion
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  5. Junior Member
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    #54
    Quote Originally Posted by networker050184 View Post
    Good explanation CaySpekko. What are your thoughts on something like BGP or LDP that does establish connections etc? Thanks for the input!
    I'm assuming you mean Border Gateway Protocol and Label Distribution Protocol, both of which according to RFC are application layer protocols on the TCP/IP model. I actually don't know a whole lot about those two protocols, but a great resource is: IP protocol suite

    One thing I'd like to point out is that if you look at a BGP packet you'll run into this:

    MAC header | IP header | TCP header | BGP header | Data ...

    Notice that the BGP header comes after the TCP header, so you can assume that it's part of the layers above the transport layer. Same goes with LDP.
    Last edited by CaySpekko; 08-24-2011 at 11:08 PM. Reason: can't spell worth beans
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  6. Senior Member alan2308's Avatar
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    #55
    Quote Originally Posted by Chris_ View Post
    I think forsaken has hit the nail on the head. The OSI model is a conceptual framework intended to assist in the demarcation of processes involved in communications. It is always going to be open to interpretation.

    My own opinion is that routing protocols are applications that exist to facilitate the functions of layer 3. In my mind anything that processes and exchanges information that has payloads encapsulated within tcp/udp headers is leaning towards being an application (I know this doesn't apply to OSPF or eigrp but there us still a layer 4 exchange of sorts within the ip encapsulation)
    Please don't attack me
    This is my thought on the matter. If it is encapsulated within TCP/UDP headers, then it has to be higher up the stack than TCP/UDP.

    And I hate to start another debate, but OSI is more than a conceptual model. Cisco IOS still routes clns and family in 12.4 and perhaps later.
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    #56
    Quote Originally Posted by alan2308 View Post
    And I hate to start another debate, but OSI is more than a conceptual model. Cisco IOS still routes clns and family in 12.4 and perhaps later.
    I'm not quite sure what point you're trying to make... clns is a layer 3 protocol, not the entire model itself.

    The OSI model is a conceptual framework that illustrates how the information flows, not an implementation guideline.
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    #57
    Quote Originally Posted by networker050184 View Post
    The end user doesn't, but someone configures them, apply policy etc. The same way you interact with any other application.

    Its really a debatable question. Some people say application, some say network. RIP for example uses UDP for communication. Does that make it an application? Guess its up to interpretation.
    Going by that, wouldn't everything be at the application layer?
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    #58
    Key Concept: It is just as much a mistake to assign too much importance to the OSI Reference Model as too little. While the model defines a framework for understanding networks, not all networking components, protocols and technologies will necessarily fall into the model’s strict layering architecture. There are cases where trying to use the model to describe certain concepts can lead to less clarity rather than more. One should remember that the OSI model is a tool, and should be used accordingly.


    Source: The TCP/IP Guide - How To Use The OSI Reference Model
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    #59
    Quote Originally Posted by networker050184 View Post
    Damn Chrome spell checker! And no worry, not heated here. I think its a great discussion with valid points from both angles.



    I'd say they are an application because they are a purpose built software used to fulfill a need for people. We could always static route everything right? Or do all of the SPF calculations manually and input the routes ourselves, but why? We can write an application that can do all of that for us. Hence routing protocols as applications that are ran by a router.

    And whats the first application listed here?

    TCP/IP model - Wikipedia, the free encyclopedia
    But if a router is a layer 3 device doesn't that make the protocols and applications it uses also level/layer 3 ?

    http://en.wikipedia.org/wiki/Router_(computing)
    "A router is considered a Layer 3 device because its primary forwarding decision is based on the information in the Layer 3 IP packet, specifically the destination IP address. "
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    #60
    Quote Originally Posted by alxx View Post
    But if a router is a layer 3 device doesn't that make the protocols and applications it uses also level/layer 3 ?

    http://en.wikipedia.org/wiki/Router_(computing)
    "A router is considered a Layer 3 device because its primary forwarding decision is based on the information in the Layer 3 IP packet, specifically the destination IP address. "
    OSI is a model, not a requirement. The key thing you're supposed to take from it is that it is a modular structure, designed to aid developers, and also to help you understand how networking works.

    A lot of apps were designed for the four layer TCP/IP model, and don't have discrete functions that easily separate to each of the 7 OSI layers (This is especially problematic on the upper layers)

    With regards to layer 7 apps being degraded to layer 3 because they end up going across a router, then by that same measure, everything can be reduced to layer 1, as it goes across the interface/wire.

    We're over-analyzing this.

    Several of us have commented that it's only a "model" and not a strict requirement that things fall neatly into.

    I'd like to think that IT peeps like myself work at Layer 9. (Regular users work at layer 8, LOL.)
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    #61
    Quote Originally Posted by instant000 View Post
    OSI is a model, not a requirement. The key thing you're supposed to take from it is that it is a modular structure, designed to aid developers, and also to help you understand how networking works.

    A lot of apps were designed for the four layer TCP/IP model, and don't have discrete functions that easily separate to each of the 7 OSI layers (This is especially problematic on the upper layers)

    With regards to layer 7 apps being degraded to layer 3 because they end up going across a router, then by that same measure, everything can be reduced to layer 1, as it goes across the interface/wire.

    We're over-analyzing this.

    Several of us have commented that it's only a "model" and not a strict requirement that things fall neatly into.

    I'd like to think that IT peeps like myself work at Layer 9. (Regular users work at layer 8, LOL.)
    ah a sheep herder

    I'm more of an embedded systems guy (embedded systems/network sensor systems/network programming) .

    As more and more switches get layer 3 switching , could argue that we're converging towards the tcpip model
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    #62
    Quote Originally Posted by networker050184 View Post
    No, you are understanding correctly, but just because a router uses it instead of a person does it mean its not an application? The purpose of RIP or BGP is to transfer routing information between routers. Same as transferring a file. Seems like an application to me.
    Just about all protocols in all layers can be configured in some way - that does not make them layer 7 protocols. Remember that applications do not work in the OSI model at all, application layer protocols do. Your web browser is an application, but http is the application layer protocol that interfaces with it.

    And regarding RIP, most material states it live in layer 3 but I see it as a layer 2 protocol. It simply transfers routing table info between direct connections (hops) one by one until the routing tables match. Is there really any knowledge of IP addresses here?
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    #63
    I dont know how RIP or OSPF works in detail... I did learn recently that OSPF does not use any TCP or UDP protocols. it works at the ip level using protocol 89.
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    #64
    Personally, I would consider them Layer 7. Though, if Cisco says Layer 3, that is what I would use on the test. Routing Protocols do not route anything. They simply do the legwork to make sure all the routers know how to route any given packet, much like how DNS does not get you to a web page, it only tells you what IP Address to use to get to the web server that hosts that web page.
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  16. Member greenerek's Avatar
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    #65
    hehehe, good discussion, I think layer3
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    #66
    Hi guys , See in cisco packet tracer simulation mode that RIP data is an application layer protocol data .But that does some configuration on layer 3 .If you dont have RIP you have to configure OSI layer 3 manually .That way "an application from OSI layer 7 does the job for the user , this case the engineer" .So the output of the RIP is layer 3 .If you think that way RIP belongs to layer 3 .But the actual functionality of RIP is in layer 7 .Believing the layer where the protocol function is ,the layer it belongs to .That way RIP is layer 7 stuff .
    Hope your rply
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