Honestly if you're unsure about basic subnetting or supernetting, you probably want to take a look at something like this:
http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a00800a67f5.shtml The simple rules are that you can't aggregate non-contiguous networks into a single prefix without covering something "extra" and that generally you can only get a "perfect" match if the number of prefixes to be aggregated is the same as the number of bits that differ between them. Also, I see many people start thinking about fancy wildcard masks that do tricky things like match multiples of 4 or something, and then when they try to do a simple summarization exercise they start thinking they can use wildcard-type matching. Aggregation, just like subnetting, requires a contiguous bitmask. On Thu, Jul 25, 2013 at 9:17 PM, Wilberth E. Lemaître < [email protected]> wrote: > As you can see on my first email, I explained the mechanism I used to get > the result of /18. > At the end of my email says: Please explain! > What is the way or "mechanism" you use to get it properly done with /21. I > can see you are CCIE and of course it is a piece of cake for you BUT I am > still in the learning process and I guess this is what this Distribution > List is for. > Can you kindly explain how you get to the conclusion of /21 in a faster > way. > Thanks in advance! > > > Date: Thu, 25 Jul 2013 20:04:41 -0500 > Subject: Re: [OSL | CCIE_RS] FW: OSPF Summarization > From: [email protected] > To: [email protected] > CC: [email protected] > > Why not get real specific? If you use a /21 subnet mask you would match > .32 - .39 > Obviously your 192 network isn't fitting in there > > > On Thu, Jul 25, 2013 at 6:55 PM, Wilberth E. Lemaître < > [email protected]> wrote: > > I was able to see the logic, if I use 3 bits the ranges would go like > these: > > > > 10.0.0.0 - 10.0.31.255 > > 10.0.32.0 - 10.0.63.255 > > 10.0.64.0 - 10.0.95.255 > > > > As we can see, they will all catch in the second range. Correct me if I am > wrong? > > > > > > From: [email protected] > > To: [email protected] > > Subject: OSPF Summarization > > Date: Thu, 25 Jul 2013 17:27:49 -0600 > > > > > > > > > > Hello community, > > > > I have a question in regards summarization. > > Let's say I have area 2 configured on a router, the advertised networks > are the following: > > > > router ospf xxx > > network 10.0.32.1 0.0.0.0 area 2 > > network 10.0.33.1 0.0.0.0 area 2 > > network 10.0.34.1 0.0.0.0 area 2 > > network 10.0.36.1 0.0.0.0 area 2 > > network 192.168.0.2 0.0.0.0 area 0 > > > > I want to summarize area 2, the mechanism I use for summarization is the > following and correct me if I am wrong. I look for the octet where the > decimal number changes, or where the bits are not equal. As we can see this > happens on the 3rd octet and I start using increments with each octet value: > > > > > 128 64 32 16 8 4 2 1 > > > > I wonder myself which increment or which number would catch all of those > into one advertisement counting from zero, in other words, how many binary > digits I have to convert to 1 in order to do the summarization. > > Based on this scenario, 32 would catch less than what we need, 64 would be > the perfect one, and I will need to convert only 2 bits (the first 2 bits) > and my subnet mask would look like 11111111.11111111.11000000.00000000 and > the network range would go like this: > > > > > 10.0.0.0 - 10.0.63.255 > > 10.0.64.0- 10.0.127.255 > > > > As we can see, if I use a subnet mask of 18, I will be including ranges > that are NOT necessary. > > > > What would be the efficient summarization in order to accomplish this > scenario? Please explain ;) > > > > Best regards, > > Wilberth > > > > > > > > > > > > > > _______________________________________________ > > For more information regarding industry leading CCIE Lab training, please > visit www.ipexpert.com > > > > Are you a CCNP or CCIE and looking for a job? Check out > www.PlatinumPlacement.com > > > > http://onlinestudylist.com/mailman/listinfo/ccie_rs > > > > -- > Marc AbelCCIE #35470(Routing and Switching) > > _______________________________________________ > For more information regarding industry leading CCIE Lab training, please > visit www.ipexpert.com > > Are you a CCNP or CCIE and looking for a job? Check out > www.PlatinumPlacement.com > > http://onlinestudylist.com/mailman/listinfo/ccie_rs > _______________________________________________ For more information regarding industry leading CCIE Lab training, please visit www.ipexpert.com Are you a CCNP or CCIE and looking for a job? Check out www.PlatinumPlacement.com http://onlinestudylist.com/mailman/listinfo/ccie_rs
