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TOPIC: Combining two supernet class c /22 networks into one /21

Combining two supernet class c /22 networks into one /21 6 years 9 months ago #33877

Hello, sammysmall here... I am a student and felt I had an understanding of subnetting and Supernetting, yet this question (part of an assignment) seems to not make sense.

Indicorp Inc. is connecting to the Internet through an Internet Service Provider (ISP). Indicorp Inc.'s public IP subnets are 203.197.16.0/22 and 203.197.20.0/22. The ISP insists that Indicorp Inc. advertise its IP subnets as a single subnet of 203.197.16.0/21. Why did the ISP suggest this?

As I understand this we have quantity 2 class C supernetted internetworks
Network: 203.197.16.0/22 11001011.11000101.000100 00.00000000 (Class C)
and Network: 203.197.20.0/22 11001011.11000101.000101 00.00000000 (Class C)
Both have available host capability of 1022
203.197.16.0/21. has a host capability of 2046

are we gaining aything here? Or what is the point to this question?
any breadcrumbs to lead me out of this forest is appreciated.
sammysmall
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Re: Combining two supernet class c /22 networks into one /21 6 years 9 months ago #33879

  • krik
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The ISP insists that Indicorp Inc. advertise its IP subnets as a single subnet of 203.197.16.0/21. Why did the ISP suggest this?
The ISP is just asking this to reduce its routing table. Internet routing tables would count +/- 315000 prefixes without summarization, thanks to summarization it counts "only" +/- 195000 prefixes. (see CIDR statistics here), all the ISP are required to try to keep them as small as possible.
Christophe Lemaire
www.exp-networks.be/blog/
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Re: Combining two supernet class c /22 networks into one /21 6 years 8 months ago #33946

krik,
Thank you for spending the time to discuss this! It is much appreciated! Your answer helps clarify real world issues that are not in the textbook!
Thank You again!
sammysmall (Rick)
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