9 Replies Latest reply: Feb 10, 2011 11:03 PM by smsnaqvi RSS

    EIGRP link bandwith.

    Rizik

      Hi everyone.

       

      Can i change bandwith settings of serial link between two eigrp enabled routers, for example one side 768 kbs, other side 256kbs. Will there occur any prblems?

       

      Regards

      Rizik

        • 1. Re: EIGRP link bandwith.
          Marko Milivojevic

          You can change it, yes. Will there be any problems really depends on what you define as a problem :-).

           

          Note that changing bandwidth to tweak EIGRP metric is rather crude method, as EIGRP will carry only the lowest bandwidth on the path. Changing the bandwidth on that link may or may not affect the total metric. Changing "delay" parameter on interfaces is more convenient, as delay is cumulative.

           

          --

          Marko Milivojevic - CCIE #18427 (SP R&S)

          Senior Technical Instructor - IPexpert

          • 2. Re: EIGRP link bandwith.
            Rizik

            Thanks Marko

            • 3. Re: EIGRP link bandwith.
              Abzal

              Heelo Rizik

              Yes Marko is right. Bandwidth it's a actully speed of the link. And delay it's a logical speed, so that you could change it.

              • 4. Re: EIGRP link bandwith.
                Marko Milivojevic

                Well.. Yes and no :-). Networks are a complex beasts :-).

                 

                Bandwidth as used by EIGRP is actually logical bandwidth, determined by either default interface bandwidth, which is only in some cases derived from the actual "speed" of the interface, or by configured "bandwidth" statement on the interface itself.

                 

                Delay on the other hand is just a pre-determined value for different interface types (it's not in any way measured), that can be modified using "delay" interface-level command.

                 

                --

                Marko Milivojevic - CCIE #18427 (SP R&S)

                Senior Technical Instructor - IPexpert

                • 5. Re: EIGRP link bandwith.
                  Abzal

                  Yes, again you're  right Marko. When I said delay, I meant bandwidth as logical, and clock rate as actually speed. My bad. Cisco recommends change delay instead bandwidth, yes? :-)

                  • 6. Re: EIGRP link bandwith.
                    Rizik

                    ))) Yes Cisco recommends that.

                    I have a little working experince, so i asked that question(changing bandwith settings 2 different bandwith 768 kbps one side, 256 kbps other side).

                     

                    Thanks all

                    Rizik

                    • 7. Re: EIGRP link bandwith.
                      Brian

                      Aloha Rizik,

                       

                      You can do this and you will affect the metric that each router calculates to get to the other router.   Here is a link to a similar discusion where ssetbob7 brought up the same issue.

                       

                      https://learningnetwork.cisco.com/message/124642#124642

                       

                      Take this basic setup:

                       

                      LAN 1 <--- 100M ---> R1 <----- serial -----> R2 <--- 100M ---> LAN 2

                      LAN 1 = 192.168.1.0/24
                      LAN 2 = 192.168.2.0/24
                      100M Ethernet delay = 100 microseconds
                      serial port delay = 20000 microseconds

                       

                      Configure 768kbps on the R1 side of the serial link and 256kbps on the R2 side.  What bandwidth will be used by each router to calculate their  metric to each other LAN subnets?

                       

                      R1 will use a bandwidth of 768 and a delay of 20100 microseconds for a metric of 3847680

                       

                      R2 will use a bandwidth of 256 and a delay of 20100 microseconds for a metric of 10514432

                       

                      I will leave you to setting this up in either PT, GNS3 or real equipment to verify.  So, yes you can configure each side to be different, but "why?" would you want to do this?

                       

                      HTH

                       

                      • 8. Re: EIGRP link bandwith.
                        Rizik

                        Hi Brian.

                        Thanks a lot. Great explanation.


                        Regards

                        Rizik

                        • 9. Re: EIGRP link bandwith.
                          smsnaqvi

                          Hi All

                           

                          In NBMA networks you have to make sure that the logical bandwidth does not exceed CIR, as the default on the serial lines are set to 1544kbps.

                           

                          Regards