If I follow what you are saying, then yes, whatever the AND'ing process of the subnet mask and the address space is what your summarization is.
Just AND your subnet mask and network statement together. That will give you your summarization range. Case in point, 137.20.1.32 255.255.255.192 Using on the last octet 00 100000 = 32 11 000000 = 192 ---------------- 00 000000 = 0 which is your summarization. Now lets get tricky and summarization 137 and 158 for the 4th octet 10001001 = 137 10011110 = 158 11100000 = 1 equals common bits, 0's unique.. = 224 Soooooo.... 10001001 = 137 11100000 = 224 100xxxxx = 128 So to summarize these 2 address's as close as possible you would use 137.20.1.128 255.255.255.224 (/27) Notice that I didn't use 137.20.1.137/27 or 137.20.1.158 /27 as if you tried you would get the error you previously mentioned. You would need to use: Area ?? Range 137.20.1.128 255.255.255.224 I hope this makes sense. I'm horrible at explaining things. You should learn sub/super-netting backwards and forwards. Not just for the test, but for real live work experience. On a side note, if you are in the habit of using a subnet calc, I would get out of that habit. I think that they are one of the worst things ever invented. It doesn't aide in the understanding of how IP addressing works, and In fact I think that it allows people to get by without the detailed Knowledge they need. JMHO though :) Thanks Larry -----Original Message----- From: Michael Witte [mailto:[EMAIL PROTECTED]] Sent: Sunday, May 19, 2002 3:08 PM To: [EMAIL PROTECTED] Subject: Re: OSPF inter-area summarization [7:44465] Larry, I had the idea right to use 255.255.255.192 mask because that is where the bit boundary is. My question is why can't you use the 137.20.1.32/26 to summarize from 32-95. What if you had a subnet zero and didn't want that summarized. Why do I have to use the 137.20.1.0 network for summarization? If we use this example: 172.20.8.0/22 00001000 >8 172.20.12.0/22 00001100 >12 ^Bit boundary=248 11111000 >248 00001000 >8 subnet 11111000 >248 mask 00001000 >8 subnet I think I see now.If you binary AND the subnet and mask and get the subnet you can use that subnet in your summarization. If the binary AND becomes zero, then you must use zero as your network in the summary command. Is this correct? I spent too much time on this and need things like this put to bed for the Lab in November. Thanks. area 11 range 172.20.8.0 255.255.248.0 Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=44493&t=44465 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
