9 Replies Latest reply: Apr 9, 2016 6:33 AM by Michel RSS

    What is EoMPLS?

    MikeH

      Hi,

       

      1) Can someone please explain to me what is EoMPLS?

       

       

      2) I am on Wendell Odoms ICND1 book page 95 and this image is throwing me off a bit.

       

      Capture1.PNG

       

       

      Why does R1 "extract ip packet and encapsulate in HDLC" before sending to R2?

       

      But if you look again at R2 and R3,

      R2 "extracts ip packet and encapsulates in Ethernet" before sending to R3

      (I am guessing this has something to do with eompls but not sure)

       

      Can someone please explain this encapsulation between R1 and R2, and then R2 and R3?

       

      Please help guys!

      And thanks so much for all the help so far with all the previous questions!

        • 1. Re: What is EoMPLS?
          vipin

          hi MikeH,

           

          1. EoMPLS is tunneling mechanism that transports Layer 2 Ethernet frames over an MPLS network. You can connect two Layer 2 networks that are in different locations, without requiring bridges, routers, or switches at the locations.
          2. MPLS is a packet-switching technology that integrates
            link layer (Layer 2) switching with network layer (Layer 3) routing. With MPLS, data is transferred over
            any combination of Layer 2 technologies, using any Layer 3 protocol, with increased scalability. MPLS
            supports different routes between a source and destination over a router-based Internet backbone.
            MPLS is a packet-switching technology that integrates link layer (Layer 2) switching with network layer (Layer 3) routing. With MPLS, data is transferred over any combination of Layer 2 technologies, using any Layer 3 protocol, with increased scalability. MPLS supports different routes between a source and destination over a router-based Internet backbone.
          3. High-level Data Link Control, a transmission protocol used at the data link layer (layer 2) of the OSI seven layer model for data communications. The HDLC protocol embeds information in a data frame that allows devices to control data flow and correct errors. HDLC is an ISO standard developed from the Synchronous Data Link Control (SDLC)standard proposed by IBM in the 1970's.

            For any HDLC communications session, one station is designated primary and the other secondary. A session can use one of the following connection modes, which determine how the primary and secondary stations interact.

          4. Normal unbalanced: The secondary station responds only to the primary station.
          5. Asynchronous: The secondary station can initiate a message.
          6. Asynchronous balanced: Both stations send and receive over its part of a duplex line. This mode is used for X.25  packet-switching networks.
          7. now, eompls and hdlc protocol is used in Wan connections. for ccna objective, learn it as wan technology, you need not study deep about it. Eompls uses ethernet header for encapsulation and hdlc uses hdlc header for encapsulation.
          8. from pc1 to R1, it encapsulate the packet by appending ethernet frame header(which includes source and destination mac address and other fields).
          9. from R1 to R2, it is a WAN link, it uses HDLC encapsulation, it adds layer 2 hdlc header, which has destination address and other fields. it doesnt send souce address. destination address is not mac address but very similar to it. after receiving the frame from pc1, R1 removes the frame header and then encapsulates with hdlc header. then sends to R2.
          10. Now, R2 received the Hdlc packet from R1.it removes the HDLC header and then encapsulates it with Eompls.it uses ethernet frame header and also other header fields.then sends it to R3.
          11. Now, R3 receives the frame and removes the Eompls header and then appends ethernet frame header then sends it to PC2.
          12. Remember, Eompls means ethernet over MPLS. it uses ethernet frame header that contains source and destination mac address.

          i hope it will clear your doubt.

          Vipin

          • 3. Re: What is EoMPLS?
            Mustafa

            the connection between R1 and R2 is serial point-to-point connection where at the physical layer uses synchronous communication between interfaces. Two standard encapsulations at the Layer 2 are HDLC or PPP. By default cisco routers use HDLC, it doesn't mean that has to be, but encapsulation must be the same on the both ends of the link. Why router R1 extract from eth in put in HDLC is because between R1 and R2 is different transport media and represent direct connection between these two routers - leased line.

            • 4. Re: What is EoMPLS?
              MikeH

              Hey Vipin,

               

              As usual thanksfor the detailsed answer it is highly appreciated!

               

              Thanks a lot man. you deserve the cisco learning forum credits!

              • 5. Re: What is EoMPLS?
                Fabiola

                Besides the comments already posted, I think the main topic or concept of that section is encapsulation and how it works. Like the paragraphs in page 94 say (under title "How Network Layer Routing Uses LANs and WANs"):

                While the network layer routing logic ignores the physical transmission details, the bits still
                have to be transmitted. To do that work, the network layer logic in a host or router must
                hand off the packet to the data link layer protocols, which, in turn, ask the physical layer
                to actually send the data. And as was described in Chapter 2, “Fundamentals of Ethernet
                LANs,” the data link layer adds the appropriate header and trailer to the packet, creating a
                frame, before sending the frames over each physical network.
                The routing process forwards the network layer packet from end to end through the network,
                while each data link frame only takes a smaller part of the trip. Each successive data
                link layer frame moves the packet to the next device that thinks about network layer logic.
                In short, the network layer thinks about the bigger view of the goal, like “Send this packet
                to the specified next device...,” while the data link layer thinks about the specifics, like
                “Encapsulate the packet in a data link frame and transmit it.” Figure 4-2 points out the key
                encapsulation logic on each device, using the same examples as shown in Figure 4-1.

                [...] "While the network layer routing logic ignores the physical transmission details, the bits still

                have to be transmitted. To do that work, the network layer logic in a host or router must

                hand off the packet to the data link layer protocols, which, in turn, ask the physical layer

                to actually send the data. And as was described in Chapter 2, “Fundamentals of Ethernet

                LANs,” the data link layer adds the appropriate header and trailer to the packet, creating a

                frame, before sending the frames over each physical network.

                The routing process forwards the network layer packet from end to end through the network,

                while each data link frame only takes a smaller part of the trip. Each successive data

                link layer frame moves the packet to the next device that thinks about network layer logic.

                In short, the network layer thinks about the bigger view of the goal, like “Send this packet

                to the specified next device...,” while the data link layer thinks about the specifics, like

                “Encapsulate the packet in a data link frame and transmit it.” Figure 4-2 points out the key

                encapsulation logic on each device, using the same examples as shown in Figure 4-1."[...]

                • 6. Re: What is EoMPLS?
                  vipin

                  Hi MikeH,

                   

                  i got 2 badges this month.

                  power knows it , power helper badges for the month of november. i am getting it for first time. i was not aiming it. it is fun to explain somebody's query.

                   

                  vipin

                  • 7. Re: What is EoMPLS?
                    MikeH

                    Your Welcome Vipin!

                    You deserve it!

                    • 8. Re: What is EoMPLS?
                      Ifere

                      Hi Guys, to the above mentioned diagram. I want to understand when wan links employ HDLC and when it uses EoMPLS?

                      • 9. Re: What is EoMPLS?
                        Michel

                        Hi Mike,

                         

                        I don't agree the explanation of this figure.

                         

                        Towards PC2 direction, the R2 router extract the IP datagram and  encapsulates it in ETH and in MPLS.

                         

                        ETH is a pseudowire depending on the client, and MPLS is a tunnel linked to the R3 destination.

                         

                        At R3 the MPLS and ETH (operator) are extracted and the IP datagram is routed. It is sent to PC2, in the access link, in an another ETH frame, with others DA, SA and VLAN than in the VPLS network.

                         

                        Sorry for that different interpretation,

                        Best regards,

                        MIchel