8 Replies Latest reply: Nov 29, 2010 12:21 PM by Mohamed Sobair RSS





      What is the difference between supernetting and summerization and CIDR?



        • 1. Re: supernetting/summerization/CIDR

          Hi CCNA


          There is a search facility on CLN.


          Our normal answer is that summarisation normally occurs on a network boundry where as super-net is a network that covers all the networks.


          So would be a summary where as would be a super-net


          Regards Conwyn

          • 2. Re: supernetting/summerization/CIDR
            Eric Belrose

            Supernetting and summarization and CIDR...


            CIDR is a condition where you no longer consider the classful boundries.  You no longer need to think of the words subnetting or supernetting really because everything is a simple division between network and host. In CIDR you could have a network with a /16 and it would be although unusual, completely legal.  Essentially turning the private Class C private network into a single Class B network.  Again I'm not sure why.  In doing so in a classful mindset it would be supernetting, but in CIDR to truly embrace it means you work classless.


            Supernetting is a classful concept.  This is where you take two networks and actually combine them.  It lifts them above their classful state.  So normally a class C network for example has 256 numbers in it (including hosts, bdcst, and network), if you supernet two class C networks you end up with 512 numbers in the grouping.  When this is done you can increase the number of hosts within the same network.


            Subnetting is the opposite where you divide the network to reduce wasted network addresses.


            Summarization is a process of making it appear as though there is only one network when there are many. So only one route is needed on router to represent multiple routes. From the perspective of the router on which you perform summarization it looks like there is only 1 network, when in fact there are multiple networks.


            That is the loosely the three concepts.  CIDR basically says bye to classful boundries. Supernetting actually takes down classful network boundries.  Summarization makes it so that you don't need as many routes to reach multiple networks, it has not much to do with the classes.  If you have a server farm on one network and a group of user workstations on another, say both are on the same network.  Then you have another group the same. Each of those could represent a route so that could be 4 routes.  But if the network numbers are close enough you can make them one route.  There is significantly more to it than this, but that is it in a nutshell.


            Say the servers are 192.168.0.XXX, then the workstations are 192.168.1.XXX those can be summarized to  This seems like supernetting but with supernetting they would be in the same network, same broadcast domain.  In this case they are in their separate broadcast domains. They are separate, but they only need one route to outside routers so at the point where they merge you summarize them together.  You could go one step futher, if you had the second group, 192.168.2.XXX and 192.168.3.XXX the whole group of them could be summarized into


            So if we were supernetting the network would be and the broadcast would be


            Because we are summarizing it is still network, and network 1

   network and network 2

   network and network 3

   network and network 4

            summarized route x 1


            I hope this isn't confusing.

            • 3. Re: supernetting/summerization/CIDR
              Eric Belrose

              To amplify Conwyns example could be a summary of a bunch of subnets of the classful network of but would be a subnet, not a supernet.  A supernet would be for example which would allow for 32 million numbers (hosts is still 2n+2) range of addresses is through to with a broadcast of in theory.


              Another key note is that in summarys, autosummary is classful and manual is either or neither whatever you prefer.  Also to do proper CIDR you also require ip classless.


              This Wiki below is well formatted.  If I understand this stuff right, CIDR is not summarization contrary to the Wiki near the bottom, the wiki and I seem to disagree on that, but where I go wrong many others I'm sure can lead us straight.  Noone is perfect, but thats why this is the learning network, not the production one.




              Good Luck and I hope again that I didn't confuse you.

              • 4. Re: supernetting/summerization/CIDR
                Eric Belrose

                I guess there is at least one more thing I think can be said to differentiate between the summarization and using CIDR.  Although CIDR is Classless Inter-Domain Routing, I guess what really differentiates the two is how they are configured.  In CIDR or when you supernet you configure using the network command in the router config mode.  So it would be network  Which would be through for hosts and the other two you know.  With a manual summary it would be ip summary-address protocol address.  With autosummary it would only summarize to the classful boundry, so it would see as a network but it wouldn't include as part of it generally.


                Lastly I keep putting public networks together with private.  This would not really and truly be possible because the private networks cannot translate to the internet.  So it would really cause alot of problems.  If you had a private public mix of 10 and 11 for example you would have to have the 10. network behind an address translation scheme anyways.  The two wouldn't truly be together so a better example would be which would be through for hosts.


                Again if you think of the /7 as supernetting you aren't really working classless.  In a classless environment there is no real supernetting or subnetting.  Only a spearation of network and host bits.


                But where class boundaries once existed if you combine multiple classful networks it is supernetting, when you make them smaller you are subnetting.  The odds of you getting ahold of public addresses en masse to do any supernetting nowadays is slim.  They are still consumed.  But as we move to IPV6 the CIDR concept really keeps its play.  Though to an extent it still uses the concept of subnetting if I remember correctly.


                Good luck and I hope I've helped you understand.

                • 5. Re: supernetting/summerization/CIDR

                  Thank You Very Much  Eric Belrose for your time and explanation.


                  I understood CIDR, auto & manual summary and subnetting.


                  Supernetting is still confused. can you please give me few examples for supernetting?



                  • 6. Re: supernetting/summerization/CIDR

                    Hi CCNA


                    The Super net of and is 8/6


                    Regards Conwyn

                    • 7. Re: supernetting/summerization/CIDR

                      I searched CIDR and got this thread, which might be above my level. I feel I understand subnet (theory and application)very well. Now a few sources have said that CIDR is similar to subnetting except that its 'classless' meaning that no longer do we need to have the net, subnet and hosts but just use the '/' notation. i am sure its more than a change in written notation. Does it have to do with whether a router's work is easier, technically with the '/', rather than the 3 part id ?

                      • 8. Re: supernetting/summerization/CIDR
                        Mohamed Sobair



                        As other's denoted , However for CIDR its almost similar to summarization. CIDR is the way of doing summarization at the upstream router or when a summarization for your internal Network done at the upstream.


                        You can refer to Cisco documentation for CIDR and it will give you the right explanation.