Someone just asked me off-list how to summarize a certain range of addresses and I thought it might be helpful to post my reply to the list. It seems like everybody has their own shortcut to doing this, but this is how I learned how to do it. Once you learn it there are plenty of shortcuts.
As far as summarization goes, to really understand what you're doing you need to think in binary. Write out those addresses in binary first: 00001010.00000001.00000001.00000000 = 10.1.1.0/24 00001010.00000001.00000011.00000000 = 10.1.3.0/24 00001010.00000001.00001110.01000000 = 10.1.14.64/26 You can see that in binary they are all the same up to the 20th bit. If you slice the above table into two pieces at the 20th bit, on the left side you are left with: 00001010.00000001.0000 This, translated back to decimal, is 10.1.0.0/20, which is your summarized address. However, this is an awful example. Those would be really bad addresses to try to summarize. A better example would be this: 10.1.0.0/24 10.1.1.0/24 10.1.2.0/24 10.1.3.0/24 00001010.00000001.00000000.00000000 00001010.00000001.00000001.00000000 00001010.00000001.00000010.00000000 00001010.00000001.00000011.00000000 You can see that these are the same up to the 22nd bit. Slice the diagram into to pieces at the 22nd bit and on the left side you are left with: 00001010.00000001.000000 which translates back to decimal as 10.1.0.0/22. Now you can see that a /22 precisely summarizes four /24s !! Cool, huh? Regards, John Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=29149&t=29149 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
