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  1. Senior Member ciscoman2012's Avatar
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    #1

    Default LAN vs WAN protocols (RIP, OSPF, EIGRP, Frame-Relay, HDLC, PPP)

    Hello,

    I was having a talk with a friend and told him about the following WAN protocols (PPP, HDLC, Frame-Relay).

    He then said that RIP and OSPF could be used over WAN as well.

    My understanding was that only WAN protocols could be used on a WAN (Frame-Relay, HDLC, PPP, ATM, etc.) and that RIP, OSPF, EIGRP, IGRP, BGP, etc. were all LAN protocols for connecting routers.

    Is my understanding of the concepts screwed up or was my friend wrong?
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  3. Member jude56g's Avatar
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    #2
    The WAN protocols you listed, FR, ATM, PPP are layer 2.
    RIP, OSPF, and BGP are layer 3 routing protocols.

    In many Cisco text examples you will see a branch office connected to the HQ over a FR or T1 connection (WAN), but a routing protocol is still enabled on top of the layer 2 transport to facilitate routing between the 2 locations.

    Another example,

    If you have a cable modem at home, there is a layer 2 DOCSIS connection between your modem and the CMTS at the Cable Co's head end, but there is also IP connectivity on top of this layer 2 connection between the CMTS and your home router.

    So to answer your question more directly, the protocols you mentioned are not mutually exclusive. Also, BGP is used almost exclusively on the WAN, however iBGP can be implemented internally within an organization.

    Hope this clears things up.
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  4. Senior Member ciscoman2012's Avatar
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    #3
    Ah, I see exactly what you're saying. They both go hand in hand correct? Except one is L2 and one is a L3 protocol? But you can't have one without the other.
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  5. Senior Member chrisone's Avatar
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    #4
    LAn vs WAN! only on PPV!
    2K14 Cert Goals: F5 101/TMOS 201, CCIE Data Center Written
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  6. CLI Junkie DragonNOA1's Avatar
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    #5
    Quote Originally Posted by jude56g View Post
    ... BGP are layer 3 routing protocols...
    I believe BGP is considered a layer 7 protocol.
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  7. Senior Member nerdydad's Avatar
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    #6
    Quote Originally Posted by ciscoman2012 View Post
    Ah, I see exactly what you're saying. They both go hand in hand correct? Except one is L2 and one is a L3 protocol? But you can't have one without the other.
    You can have the L2 without a L3 protocol running, you could use static routes instead of a routing protocol, but you can not run L3 without L2.
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  8. Skilled Hamburglar Monkerz's Avatar
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    #7
    Quote Originally Posted by DragonNOA1 View Post
    I believe BGP is considered a layer 7 protocol.
    We could really discuss this for days. Everyone will have a different opinion. Mine is, that BGP may be an application that affects routing, but it transports at L4, thus I believe it is a L4 protocol...
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  9. Member jude56g's Avatar
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    #8
    Quote Originally Posted by Monkerz View Post
    We could really discuss this for days. Everyone will have a different opinion. Mine is, that BGP may be an application that affects routing, but it transports at L4, thus I believe it is a L4 protocol...
    Whats the Cisco answer?
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  10. Netlurker cisco_trooper's Avatar
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    #9
    There seems to be some confusion between transport protocols and other protocols...Routing Protocols are not layer 3 protocols, though they provide services for layer 3 protocols, the most prolific being IP. BGP is a routing protocol that allows dynamic routing table updates of IP destinations on a large scale. BGP utilizes TCP port 179 in its communications but just because it uses TCP does not make it a layer 4 protocol. In terms of layer 4 protocols that ride on IP, there will be IP protocol number embedded in the IP header that distinguishes the layer 4 protocol in use. In a BGP packet you will find this protocol number to be IP protocol 6, the IP protocol number for TCP. If you want to find out if this TCP packet is a BGP routing protocol update you are going to have to look at the payload of that packet. A routing protocol is going to live above layer 4. In terms of the TCP/IP model the next logical layer is layer 7. Hope that's enough info to get your wheels turning.
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  11. Senior Member
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    #10
    Quote Originally Posted by ciscoman2012 View Post
    Hello,

    I was having a talk with a friend and told him about the following WAN protocols (PPP, HDLC, Frame-Relay).

    He then said that RIP and OSPF could be used over WAN as well.

    My understanding was that only WAN protocols could be used on a WAN (Frame-Relay, HDLC, PPP, ATM, etc.) and that RIP, OSPF, EIGRP, IGRP, BGP, etc. were all LAN protocols for connecting routers.

    Is my understanding of the concepts screwed up or was my friend wrong?

    As one of the mates here told you RIP,OSPF,EIGRP and IGRP also BGP are layer 3 routing protocols. On the other hand PPP, HDLC and FR are
    layer 2 encapsulation protocols used to transmit layer 3 packets across WAN links. Those links could be dedicated leased lines where
    PPP and HDLC are implemented or FR which applies its own encapsulation protocol.
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  12. Senior Member Mike-Mike's Avatar
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    #11
    Quote Originally Posted by chrisone View Post
    LAn vs WAN! only on PPV!
    this cracked me up
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  13. Netlurker cisco_trooper's Avatar
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    #12
    Keep in mind, a layer 3 protocol won't be using another layer 3 protocol to communicate and won't be defined in terms of another layer 3 protocol. If protocol A uses protocol B at layer C to communicate it stands to reason that protocol A operates at a layer above layer C. Take a look at how the routing protocols operate. They are using IP multicast to establish neighborships in many cases. Some are using TCP sessions, which obviously ride on IP. A routing protocol does not operate at layer 3.
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  14. Grind time, gotta eat MrBrian's Avatar
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    #13
    The discussion of what layers RIP, BGP, OSPF, and EIGRP operate at is pretty interesting I think. It's weird. It's almost as if there is no definitive answer. I think it's more important to understand the functions of each protocol, and the order in which they're all encapsulated, than trying to place each protocol at a concrete layer. I agree with cisco_trooper though, they are not layer 3 protocols. IP is a layer 3 protocol and RIP, BGP, EIGRP, and OSPF give data to IP to be encapsulated in an IP header.

    When you look at the protocol field in the IP header, it identifies the "higher-layer protocol." In other words, what protocol gave data to IP, and therefore not be at the same layer (however, ICMP nixes that logic). IP uses the protocol field to demultiplex incoming datagrams. A protocol field of 88 means that EIGRP data is encapsulated within.. a protocol field of 89 means that OSPF data is encapsulated within. When the destination gets the datagram, it would strip the IP header and then give the data to that protocol module on its own system. However, layer 4 is also called the Transport layer, but really only UDP and TCP are used for transport. A protocol field of 17 is for UDP and 6 is for TCP. The destination will give the data from the IP header to its own TCP or UDP module, then based on the destination port field, it will know what application to send the data to.

    EIGRP and OSPF data is really just encapsulated within IP, but not really a transport protocol that can send application data... so I'd say it's a layer 4 protocol, but not a transport protocol. This is my understanding.. anyone feel free to enlighten me though. Just thinking through it gives me more and more of an understanding.

    RIP and BGP, however, use transport protocols.. so are actually considered application layer protocols. RIP is encapsulate within UDP and uses port 520. which is then encapsulated within IP, so it's not layer 3 or 4. Since it's above layer 4, it's just considered an application protocol. BGP uses TCP port 179, so it's also an application layer protocol.

    A confusing twist to this, is that ICMP uses protocol number 1 in the protocol field of an IP header.. but ICMP is still considered a layer 3 protocol.. even though it is encapsulated within IP.
    Currently reading: Internet Routing Architectures by Halabi
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