About CIDR (route summarization)

[pretendermanu]

I have been reading about summarizing routes and i just don't find a pattern on how that is done. Any one knows on any link where i can get more informantion on what can or can't be done when summarizing routes?

Thanks for your time!

[Josef Oduwo]

Classless Inter-Domain Routing or CIDR was introduced to improve both routing scalability and address space utilization in the Internet.

CIDR moves way from the traditional IP classes (Class A, Class B, Class C, and so on). In CIDR, an IP network is represented by a prefix, which is an IP address and an indication of the length of its mask. Length means the number of mask bits, counting from the left, that are set to one. So the network 172.16.0.0 255.255.0.0 can also be written as 172.16.0.0/16 with "/16" being the mask or 16 bits set to one, if you count from the left.

If you have the network 172.16.0.0/16, then you can assign the (sub)networks 172.16.1.0/24, 172.16.2.0/24 etc to your departments or users. And all you would need to advertise to outwardly would be 172.16.0.0/16, all the subnetworks are "summarized" as this address.

Visit this site http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a00800a67f5.shtml for more on IP addressing.

Cheers,

Josef.

PS - rate if it helps ;-)

[pretendermanu]

Thank you for your reply. I have been reeding info on that site and i am starting to see the light (pattern).