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  1. Went to the dark side.... Moderator networker050184's Avatar
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    #26
    While I agree the Cisco answer is Layer 3, I don't think the original definition of application layer has to do with strictly human interaction. I prefer this definition.

    "In TCP/IP, the Application Layer contains all protocols and methods that fall into the realm of process-to-process communications across an Internet Protocol (IP) network. Application Layer methods use the underlying Transport Layer protocols to establish host-to-host connections."

    That would definitely include routing protocols, no?

    But yes, I can see where you are coming from in a strictly OSI sense. But I still believe routing protocols, BGP and RIP especially are applications.
    Last edited by networker050184; 08-24-2011 at 08:30 PM.
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    #27
    Wow guys wtf have I just read? I guess we're a little bored today!
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    #28
    Oh, well, if we're sourcing Wikipedia, then by all means -

    Network Layer - Wikipedia, the free encyclopedia

    Arguments over, wikipedia says RIP and BGP are layer 3!
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  5. Went to the dark side.... Moderator networker050184's Avatar
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    #29
    Where would you put LDP on the OSI model? Not trying to be difficult, curious what your opinion is on that?
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  6. Senior Member SdotLow's Avatar
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    #30
    Quote Originally Posted by networker050184 View Post
    While I agree the Cisco answer is Layer 3, I don't think the original definition of application layer has to do with strictly human interaction. I prefer this definition.

    "In TCP/IP, the Application Layer contains all protocols and methods that fall into the realm of process-to-process communications across an Internet Protocol (IP) network. Application Layer methods use the underlying Transport Layer protocols to establish host-to-host connections."
    Here's how I look at it.

    When I send a file to you, it doesn't have anything to do with a routing protocol until that data hits the router. If you and I were on the same switch, that data would never be introduced to a routing protocol.

    I'm struggling to see how a routing protocol interfaces with the application layer unless you're implying IOS is the reason.


    But yes, I can see where you are coming from in a strictly OSI sense. But I still believe routing protocols, BGP and RIP especially are applications.
    So BGP and RIP are themselves applications???
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    #31
    Let's say I have "hub" router with static routes pointing the networks in my organization to the proper next hop.

    Every 10 minutes or so, I have a script that pushes route changes to this router via tftp. This is certainly completely transparent to the end user.

    Is that,then, a L3 function?

    Quote Originally Posted by Forsaken_GA View Post
    I see we need to go back to basics

    Internetworking Basics - DocWiki

    I'm not going to opine whether or not Cisco is the authority when it comes to the OSI model, but in the context of how the OSI model applies to their exam, I accept them as an expert opinion.

    And Cisco says that Application layer is closest to the user, it requires direct interaction.

    Given that, then I'd say routing protocols certainly do not apply as Application layer technology. The user does not directly interact with the routing protocols, only the nodes they exchange routes with do, and that's at a lower level, any visibility

    So IOS or the client we use to login to IOS in order to activate the routing protocols? Certainly applications. The routing protocols themselves? Absolutely not.

    Anything else is just semantical lawyering, and if you feel your opinion is correct, you should be making that case to the ISO, ITU-T, and Cisco.
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  8. Went to the dark side.... Moderator networker050184's Avatar
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    #32
    Quote Originally Posted by SdotLow View Post
    So BGP and RIP are themselves applications???
    Depends who you are asking, me or Foresaken.
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  9. Senior Member SdotLow's Avatar
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    #33
    Quote Originally Posted by creamy_stew View Post
    Let's say I have "hub" router with static routes pointing the networks in my organization to the proper next hop.

    Every 10 minutes or so, I have a script that pushes route changes to this router via tftp. This is certainly completely transparent to the end user.

    Is that,then, a L3 function?
    It would be as much of a L3 function as manually typing it in through Telnet would be. The user is still setting up the application to alter the router through application layer protocols.

    A static route changing on a router isn't a routing protocol, I wouldn't think.
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  10. Senior Member MrRyte's Avatar
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    #34
    Maybe my post was a little blunt; but I still can't see how it can be considered an application......

    The only time that a person would interact (either by console or telnet)with the routing protocols is when they are configuring them or troubleshooting them. Otherwise; they are supposed to be working behind the scenes ensuring the correct routing of packets.
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    #35
    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.
    But UDP is connectionless transport layer 4, so is a routing protocol a transport layer mechanism? jk

    OSI layers can become blurred and a lot of fun to be had with the circular debates!
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  12. Senior Member SdotLow's Avatar
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    #36
    Quote Originally Posted by MrRyte View Post
    The only time that a person would interact (either by console or telnet)with the routing protocols is when they are configuring them or troubleshooting them. Otherwise; they are supposed to be working behind the scenes ensuring the correct routing of packets.
    I would say that a even if you're using telnet to configure a router, you're not interacting with a layer 3 protocol so to speak. The protocol is what it (the protocol) does, propagating routing tables and assigning packets to x/y/z route.

    Network: Can you elaborate on why BGP or RIP would be considered an application?
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  13. Senior Member Turgon's Avatar
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    #37
    Quote Originally Posted by SdotLow View Post
    It would be as much of a L3 function as manually typing it in through Telnet would be. The user is still setting up the application to alter the router through application layer protocols.

    A static route changing on a router isn't a routing protocol, I wouldn't think.
    A static route is not a routing protocol.
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  14. Senior Member SdotLow's Avatar
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    #38
    Quote Originally Posted by Turgon View Post
    But UDP is connectionless transport layer 4, so is a routing protocol a transport layer mechanism? jk

    OSI layers can become blurred and a lot of fun to be had with the circular debates!
    I've read that they get blurred from interaction, from say layer 2 to 3 in a switch or what have you. But how does it get blurred from layer 3 to 7?

    I'm honestly trying to wrap my head around what I'm missing here. Forsaken had me thinking I wasn't crazy but then Turgon jumps in and mixes it up again.
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  15. Senior Member Turgon's Avatar
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    #39
    Quote Originally Posted by networker050184 View Post
    Where would you put LDP on the OSI model? Not trying to be difficult, curious what your opinion is on that?
    Good one. A lot of literature passes it off as layer 2.5
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  16. Senior Member Turgon's Avatar
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    #40
    Quote Originally Posted by SdotLow View Post
    I've read that they get blurred from interaction, from say layer 2 to 3 in a switch or what have you. But how does it get blurred from layer 3 to 7?

    I'm honestly trying to wrap my head around what I'm missing here. Forsaken had me thinking I wasn't crazy but then Turgon jumps in and mixes it up again.
    Lots of opportunities to blur higher up too. Coders

    The TCP/IP Guide - OSI Reference Model Networking Layers, Sublayers and Layer Groupings


    'In some areas, the layers are so closely related that the lines between them become blurry. This is particularly the case when looking at the higher layers; many technologies implement two or even all three of these layers, which is another reason why I feel they best belong in a group together. One important reason why the distinctions between layers five through seven are blurry is that the TCP/IP protocols are based on the TCP/IP model, which combines the functions of layers five through seven in a single, thick layer.'

    Sorry to mess with your head!
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  17. Went to the dark side.... Moderator networker050184's Avatar
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    #41
    Quote Originally Posted by SdotLow View Post
    I would say that a even if you're using telnet to configure a router, you're not interacting with a layer 3 protocol so to speak. The protocol is what it (the protocol) does, propagating routing tables and assigning packets to x/y/z route.
    The routing protocol does not assign packets to routes. All the routing protocol does is exchange the information and run it against a best path selection algorithm. The forwarding process then uses that information to actually route the traffic.

    I'd say BGP is an application because it take NLRI (network layer reach ability information), runs a best path selection algorithm and then offers that information to the router to form the routing table. The NLRI can be straight up IPv4, VPNv4 etc.

    Same with RIP. Its just an application used to exchange information and run an algorithm against it. The router uses that output to build its routing table. The routing protocol itself isn't doing any routing function on the router.

    My example with LDP is the same way. Its an application designed to transfer MPLS label information between routers. Just because it happens to carry labels doesn't mean it operates on the same layer as the labels used for forwarding.
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  18. Went to the dark side.... Moderator networker050184's Avatar
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    #42
    Quote Originally Posted by Turgon View Post
    Lots of opportunities to blur higher up too. Coders

    The TCP/IP Guide - OSI Reference Model Networking Layers, Sublayers and Layer Groupings


    'In some areas, the layers are so closely related that the lines between them become blurry. This is particularly the case when looking at the higher layers; many technologies implement two or even all three of these layers, which is another reason why I feel they best belong in a group together. One important reason why the distinctions between layers five through seven are blurry is that the TCP/IP protocols are based on the TCP/IP model, which combines the functions of layers five through seven in a single, thick layer.'

    Sorry to mess with your head!
    Agreed. Its not as straight forward as it would seem if you look deeper into it and the layers blur together haha.
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  19. Senior Member Turgon's Avatar
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    #43
    Quote Originally Posted by networker050184 View Post
    The routing protocol does not assign packets to routes. All the routing protocol does is exchange the information and run it against a best path selection algorithm. The forwarding process then uses that information to actually route the traffic.
    Pretty much. Routing protocols offer routers tables to query by a process on the router. Essentially you are determining which exit interface on the device to use to get to an IP destination that may be close by or many hops away. Once that is determined the correct layer 2 encapsulation type has its way. Ethernet, serial, frame relay, whatever. Reading about RIB and FIB might help anyone struggling with some of this.
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    #44
    To really understand the OSI stack you need to understand network programming.

    One of the reasons for the OSI model to help programmers and manufactures have a model to follow when implementing network interactions, so that networks are interoperable without to much proprietary configuration.

    OSPF and RIP advertisements and hellos are at most encasulated into a layer 3 packet, then the packet is pushed into the MAC layer, where it's encapsulated with a mac header, then pushed on the physical wire, then to the other router, when de-encasulates the mac, sees the ip header, strips that off. The data left over is sent straight away to the OSPF process without transending other network layers (the router knows it's ospf because it came from multicast 224.0.0.5 and 224.0.0.6). At most it uses layer 3. 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.

    Telnet, is used to test all the way upto layer 7, and this is a good test question. If telnet is successful, then you know the entire 7 layer stack is working properly.

    The flow is somewhat as follows:
    Application: The application will request to the OS that it needs a socket for communication over the network.

    Presentation: the telnet app determines that it's going to send data over the link using plain text, probably using an array as a data structure.

    Session: Telnet argues with the other end and establish a method for communication, the actual datagram isn't modified in this layer, but the app will send communication requests out of the socket, and wait for a response back, before it tries to forward data.

    Transport: telnet uses TCP port 23 the layer 4 datagram encapsulates the raw telnet data

    Network: IP addresses encasulate the layer 4 datagram (it's all part of the ip header)

    Datalink: mac address encapsulate the layer 3 packet

    Physical: the mac frame is sent out the wire as bits

    Even if you run OSPF on Windows Server, it'll listen on 224.0.0.5 and 224.0.0.6, and send the data from the IP packet straight to it's OSPF process, and doesn't have to do all the higher layer networking stuff.
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  21. Senior Member Turgon's Avatar
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    #45
    Quote Originally Posted by CaySpekko View Post
    To really understand the OSI stack you need to understand network programming.

    One of the reasons for the OSI model to help programmers and manufactures have a model to follow when implementing network interactions, so that networks are interoperable without to much proprietary configuration.

    OSPF and RIP advertisements and hellos are at most encasulated into a layer 3 packet, then the packet is pushed into the MAC layer, where it's encapsulated with a mac header, then pushed on the physical wire, then to the other router, when de-encasulates the mac, sees the ip header, strips that off. The data left over is sent straight away to the OSPF process without transending other network layers (the router knows it's ospf because it came from multicast 224.0.0.5 and 224.0.0.6). At most it uses layer 3. 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.

    Telnet, is used to test all the way upto layer 7, and this is a good test question. If telnet is successful, then you know the entire 7 layer stack is working properly.

    The flow is somewhat as follows:
    Application: The application will request to the OS that it needs a socket for communication over the network.

    Presentation: the telnet app determines that it's going to send data over the link using plain text, probably using an array as a data structure.

    Session: Telnet argues with the other end and establish a method for communication, the actual datagram isn't modified in this layer, but the app will send communication requests out of the socket, and wait for a response back, before it tries to forward data.

    Transport: telnet uses TCP port 23 the layer 4 datagram encapsulates the raw telnet data

    Network: IP addresses encasulate the layer 4 datagram (it's all part of the ip header)

    Datalink: mac address encapsulate the layer 3 packet

    Physical: the mac frame is sent out the wire as bits

    Even if you run OSPF on Windows Server, it'll listen on 224.0.0.5 and 224.0.0.6, and send the data from the IP packet straight to it's OSPF process, and doesn't have to do all the higher layer networking stuff.
    Very good point. I supported FX trading app developers and testors for a number of years. For networkers I recommend books on windows sockets programming and Stevens. Once you get into heavy weight real time trading environments it pays to know a good deal.
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  22. Went to the dark side.... Moderator networker050184's Avatar
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    #46
    Good explanation CaySpekko. What are your thoughts on something like BGP or LDP that does establish connections etc? Thanks for the input!
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  23. Senior Member MrXpert's Avatar
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    #47
    Quote Originally Posted by SdotLow View Post
    You didn't look very hard. You could have gotten the answer on Wikipedia.

    An application layer protocol is something like Telnet, HTTP, or FTP. Something communicates with an application, so to speak. OSPF and RIP are never seen by an application, or the application layer.

    With that being said, you're posting in the CCENT/CCNA forums about a very easy question that can be found in your study book(s). I'd suggest looking there.
    Put it this way "I looked hard enough to see it was worthy of debate"
    i have seen at least two different sources stating different things including a discussion about it on the cisco forums website between CCNP and CCNAs who also appear to be not so sure about it
    Last edited by MrXpert; 08-24-2011 at 11:19 PM.
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  24. Senior Member MrXpert's Avatar
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    #48
    Quote Originally Posted by hiddenknight821 View Post
    You got to be joking. It's a silly debate and you're asking us for help?! This is not some tag-team wrestling. Looks like both of you need go back to the books and review on OSI layer.
    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
    Last edited by MrXpert; 08-24-2011 at 11:11 PM.
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  25. Senior Member MrXpert's Avatar
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    #49
    Quote Originally Posted by MrRyte View Post
    And HOW EXACTLY does the end user interact or use RIP, OSPF or any other routing protocol?

    I think that the answer is obvious....
    crickey if you passed the ICND1 then i'll have no problem with it then
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    #50
    Quote Originally Posted by networker050184 View Post
    Where would you put LDP on the OSI model? Not trying to be difficult, curious what your opinion is on that?
    Like you, I'd put it at layer 2.5 because that's where it would logically fit.

    If I had to make a choice between layer 2 and layer 3, I'd put it at layer 3, as label lookup/forwarding is very similar to ip lookup/forwarding, given that labels are normally tied to a prefix, which means they're tied to the routing table.

    As for the rest of it, CaySpekko made the arguments I would have (and better than I would have) so I'll let it alone
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