9 Replies Latest reply: Dec 29, 2010 9:14 PM by Jared RSS

    Collapse Core Design

    Steven Williams

      What is the draw back of a collapse core design vs a traditional Core, Distribution, Access design?

        • 1. Re: Collapse Core Design

          Well, each layer is supposed to perform a specific function.  This way, sufficient resources can be dedicated to those functions.  So, a collapsed core design basically combines those layers so that one switch performs 2 of the 3 layers, or even all 3!  A switch that is meant to just switch packets as fas as it can, now has to deal with the overhead of running a routing protocol, or processing an ACL.  That takes up resources that could be used or the basic functions the core layer alone would provide.


          If the environment is small enough, it works fine.  The other thing you need to keep in mind is redundancy.

          • 2. Re: Collapse Core Design
            Steven Williams

            Lets say the access layers are layer 3 devices, can you process ACL's there instead?

            • 3. Re: Collapse Core Design

              Depending, on your set up... Yes.  But, if you are studying for the CCDA, you will want to go by cisco's design recommendations... Even if real world experience or financial limitations tell you otherwise.  For the purpose of the exam, ACLs are a distribution layer function.

              • 4. Re: Collapse Core Design
                Steven Williams

                But I was always under the impression that we want to push layer 3 as close to the access layer as we can....Is this correct?

                • 5. Re: Collapse Core Design

                  Heneheh, depends on your design and what you are trying to accomplish.  Pushing layer 3 close tothe access layer helps in shrinking the size of your broadcast domains, but is that a design requirement in the business or technical goals?


                  Trust me when I say that you want to go by cisco's design recommendations when doing CCDA.  You will fail that test if you don't.

                  • 6. Re: Collapse Core Design
                    Steven Williams

                    Its just so funny that they want us to go by their design, but they want tests to be real life. LOL. I wonder if these people making tests and stuff actually go to real businesses.

                    • 7. Re: Collapse Core Design

                      Well, in the perfect world, I understand where Cisco is coming from with ther design recommendations.  But usually, in the real world, the business constraint of money typically wins and you just can't do everything that is reconnended in a design.  So if cisco says to do it their way, but they also test you on determining the best design that fits in the business and technical goals and constraints... And those factors happen to not align with Cisco's recommendations., what do you do? 

                      Both are correct testing objectives, but they seem to conflict with each other.  I failed and struggled with the CCDA because of it's theoretical nature.  I am more of a practical thinker and so that was against me.  It is still a good test and a good cert.  One that I will try for again sometime in the future.

                      • 8. Re: Collapse Core Design

                        Great discussion, design is fun. 



                        Why push it to the access layer?  WHy not push out a modular distribution layer instead?  What does L3 at the access give you?  Why would you not want to get rid of STP alltogether? 



                        As Jared said, money plays a big part here, but in the CCDA test, it's all about Cisco Best Practices and The Cisco Way.  Unfortunately once you pass the test, and even when you move on to the CCDP, you tend to have to "unlearn" some things when it comes to production.  Some of their design goals are more like Holy Grails for many companies - something to shoot for but never really expect to get there in a full fledged manner. 

                        • 9. Re: Collapse Core Design

                          Well stated Travis!  The next time I  sit CCDA, and I will, I need to think holy Grail and not real life!