6 Replies Latest reply: Oct 31, 2012 4:30 PM by Joshua Johnson - CCNP R&S RSS

    80/20 or 20/80 rule




      I am trying to understand the 20/80 rule and the 80/20 rule.


      This is what I think it means -


      The 80/20 rule is the old network infastructure. An Accountant sits in his area and he is connected to his/her network

      The 20/80 rule is the new network infastrucure. An Accountant sits whereever they want as 80% of work croses the network and is internet related.



        • 1. Re: 80/20 or 20/80 rule

          This rule was important when BW was a premium and when dramatic measures were required to limit broadcast traffic between LANs. Scenario - A LAN used to be as low as 1Mbps and so bridges would be employed to limit broadcast traffic within workgroups or departments and so maximise the balance of the BW for users.  These days, users require data to be shared beyond the workgroups and use the Internet more so the traffic mix is 20%local 80%external.  HTH

          • 2. Re: 80/20 or 20/80 rule

            I think this started in the "way back when" as networks were young.  The theory was that 80% of the traffic stayed in the local network or segment, and 20% of the traffic would leave (for the backbone, for example).  At one point I heard people stating that the opposite was now true (sort of a 20/80 rule), but I'd be surprised if that is even the case.  As this rule of thumb was somewhat of a method for estimating backbone capacity need, it is a bit dated as there are now better ways of doing this.


            Given that the current trend is towards terms such as "borderless networking" and "converged infrastructure", I'd be surprised if major players are still using that type of rule.  Though I don't have first-hand experience, I'd hazard to say that distributed services/data centers, "cloud" services, and the like have rendered it mostly obsolete, or at least highly dependent upon the enterprise's network architecture.


            (Edited to add:  Albert beat me to the punch, and included an important nugget of info regarding premium cost of bandwidth in the "way back when".  Good job, sir!)

            • 3. Re: 80/20 or 20/80 rule

              How much of this will be in the CCNP switch exam. It's just that I don't want to spend my time reading chaptor afteer chaptor

              • 4. Re: 80/20 or 20/80 rule

                you do not have to read chaptor; jsut read chapter 


                Everything covered in the book is "Go" for exam.

                • 5. Re: 80/20 or 20/80 rule
                  Paul Stewart  -  CCIE Security

                  I would be prepared to understand that. It is core to the local VLAN design. The old recommendation was end to end vlans based on role. As rescources moved farther from users, the shift was made from [approximately] 80/20 to 20/80. As such, Cisco's recommendation changed for various reasons (cleaner design, easier troubleshooting, convergence, can help eliminate STP, etc). As such, now VLANs may be local to a switch block or even a switch. When the PC connected ports are on a single switch, you can easily eliminate the layer two connections between the distribution switches. This removes the dependence on STP for the affected VLANs. The 80/20 versus the 20/80 rule is a simple piece of some more complex topics around design (that certainly may be on the exam).

                  • 6. Re: 80/20 or 20/80 rule
                    Joshua Johnson - CCNP R&S

                    I employed the 20/80 rule when designing my companies new site... VLANs based on geography and NOT end to end is the way to go for ease of management and eliminating possible site wide broadcast storms.