1 / 45

Chapter 6 VLSM and CIDR

Chapter 6 VLSM and CIDR. CIS 82 Routing Protocols and Concepts Rick Graziani Cabrillo College graziani@cabrillo.edu Last Updated: 2/24/2009. Note. My web site is www.cabrillo.edu/~rgraziani.

bly
Download Presentation

Chapter 6 VLSM and CIDR

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Chapter 6 VLSM and CIDR CIS 82 Routing Protocols and Concepts Rick Graziani Cabrillo College graziani@cabrillo.edu Last Updated: 2/24/2009

  2. Note • My web site is www.cabrillo.edu/~rgraziani. • For access to these PowerPoint presentations and other materials, please email me at graziani@cabrillo.edu. • Additional information is in the Notes section of this PowerPoint.

  3. For further information • This presentation is an overview of what is covered in the curriculum/book. • For further explanation and details, please read the chapter/curriculum. • Book: • Routing Protocols and Concepts • By Rick Graziani and Allan Johnson • ISBN: 1-58713-206-0 • ISBN-13: 978-58713-206-3

  4. Topics • Classful and Classless Addressing • Classful IP Addressing • Classful Routing Protocols • Classless IP Addressing • Classless Routing Protocols • VLSM • VLSM in Action • VLSM and IP Addresses • CIDR • Route Summarization • Calculating Route Summarization

  5. Classful and Classless Addressing Classful IP Addressing Classful Routing Protocols Classless IP Addressing Classless Routing Protocols

  6. Classful and Classless Routing Protocols • Routing protocols: • classful or classless. • This is a result of the evolution from classful to classless IPv4 addressing. • As networks began to use classless addressing, classless routing protocols had to be modified or developed to include the subnet mask in the routing update.

  7. Classful IP Addressing • As of January 2007, there were over 433 million hosts on the Internet. • IPv4 32-bit address space would now be exhausted if it were not for? • VLSM - 1993 (RFC 1519) • CIDR - 1993 (RFC 1519) • Network Address Translation (NAT) - 1994 (RFC 1631) • Private addressing- 1996 (RFC 1918)

  8. High-Order Bits? • Only these three choices - No medium sized networks . • How did they actually come up with these ranges? • How can a device such as a router quickly determine the subnet mask of the IP address? • By examining the first few bits of the address.

  9. Classful Routing Protocol Classful Routing Protocols • Is the subnet mask included in the routing update? • No • How does the router determine the mask? • Value of the first octet (first 3 bits of the address) or Interface Mask

  10. Classful Routing Protocol R2 applies s0/0/0’s /24 subnet mask (same major network) R1 sends a subnet address out s0/0/0 (same major network)

  11. Classful Routing Protocol R2 sends a summarized route out s0/0/1 (different major network) R3 applies the default /16 subnet mask (different major network)

  12. Moving TowardClassless Addressing • By 1992, IETF had serious concerns about: • The exponential growth of the Internet and Internet routing tables. • Eventual exhaustion of 32-bit IPv4 address space. • 1993, IETF introduced classless interdomain routing (CIDR) (RFC 1517). • More efficient use of IPv4 address space • Prefix aggregation, which reduced the size of routing tables

  13. CLASS A ISPs no longer restricted to three classes. Can now allocate a large range of network addresses based on customer requirements CLASS B 11111111.00000000.00000000.00000000 /8 (255.0.0.0) 16,777,216 host addresses 11111111.10000000.00000000.00000000 /9 (255.128.0.0) 8,388,608 host addresses 11111111.11000000.00000000.00000000 /10 (255.192.0.0) 4,194,304 host addresses 11111111.11100000.00000000.00000000 /11 (255.224.0.0) 2,097,152 host addresses 11111111.11110000.00000000.00000000 /12 (255.240.0.0) 1,048,576 host addresses 11111111.11111000.00000000.00000000 /13 (255.248.0.0) 524,288 host addresses 11111111.11111100.00000000.00000000 /14 (255.252.0.0) 262,144 host addresses 11111111.11111110.00000000.00000000 /15 (255.254.0.0) 131,072 host addresses 11111111.11111111.00000000.00000000 /16 (255.255.0.0) 65,536 host addresses 11111111.11111111.10000000.00000000 /17 (255.255.128.0) 32,768 host addresses 11111111.11111111.11000000.00000000 /18 (255.255.192.0) 16,384 host addresses 11111111.11111111.11100000.00000000 /19 (255.255.224.0) 8,192 host addresses 11111111.11111111.11110000.00000000 /20 (255.255.240.0) 4,096 host addresses 11111111.11111111.11111000.00000000 /21 (255.255.248.0) 2,048 host addresses 11111111.11111111.11111100.00000000 /22 (255.255.252.0) 1,024 host addresses 11111111.11111111.11111110.00000000 /23 (255.255.254.0) 512 host addresses 11111111.11111111.11111111.00000000 /24 (255.255.255.0) 256 host addresses 11111111.11111111.11111111.10000000 /25 (255.255.255.128) 128 host addresses 11111111.11111111.11111111.11000000 /26 (255.255.255.192) 64 host addresses 11111111.11111111.11111111.11100000 /27 (255.255.255.224) 32 host addresses 11111111.11111111.11111111.11110000 /28 (255.255.255.240) 16 host addresses 11111111.11111111.11111111.11111000 /29 (255.255.255.248) 8 host addresses 11111111.11111111.11111111.11111100 /30 (255.255.255.252) 4 host addresses 11111111.11111111.11111111.11111110 /31 (255.255.255.254) 2 host addresses 11111111.11111111.11111111.11111111 /32 (255.255.255.255) “Host Route” CLASS C

  14. CIDR and Route Summarization • CIDR = Route summarization • A supernet summarizes multiple network addresses with a mask less than the classful mask.

  15. CIDR and Route Summarization • 192.168.0.0/23, 192.168.2.0/23, 192.168.4.0/22, and 192.168.8.0/21 are all subnets of 192.168.0.0/20

  16. CIDR and Route Summarization • Propagating VLSM and supernet routes requires a classless routing protocol, because the subnet mask can no longer be determined by the value of the first octet.

  17. Classless Routing Protocol • Classless routing protocols include the subnet mask with the network address in their routing updates.

  18. Classless Routing Protocol • 172.16.0.0/16, 172.17.0.0/16, 172.18.0.0/16, and 172.19.0.0/16 summarized as 172.16.0.0/14. • What is this called? (Subnet mask is less than the classful default mask.) • Supernet • /14 (255.252.0.0) subnet mask is included in the routing update. /14

  19. VLSM VLSM in Action VLSM and IP Addresses

  20. VLSM • The network 10.0.0.0/8 has been subnetted using the subnet mask of /16, which gives the potential of 256 subnets: 10.0.0.0/16 10.1.0.0/16 10.2.0.0/16 . . . 10.255.0.0/16

  21. VLSM • Any of these /16 subnets can be subnetted further. • For example the 10.1.0.0/16 subnet is subnetted again using the /24 mask.

  22. 10.1.0.0/16 subnet is subnetted again using the /24 mask • 10.2.0.0/16 subnet is also subnetted again with a /24 mask. • 10.3.0.0/16 subnet is subnetted again with the /28 mask. • 10.4.0.0/16 subnet is subnetted again with the /20 mask.

  23. A 10.1.4.10/24 • Individual host addresses are assigned from the addresses of “sub-subnets.” • What would be a valid Host IP address for Host A?

  24. VLSM: A different way to look at it • Subnet 10.0.0.0/8 into /16 subnets. • Subnet 10.1.0.0/16 into /24 subnets.

  25. VLSM: A different way to look at it • Subnet 10.2.0.0/16 into /24 subnets. • Subnets ranging from 10.2.0.0/24 to 10.2.255.0/24

  26. VLSM: A different way to look at it • Subnet 10.3.0.0/16 is further subnetted with a /28 mask • 14 host addresses per subnet. • Subnets ranging from 10.3.0.0/28 to 10.3.255.240/28.

  27. VLSM: A different way to look at it • Subnet 10.4.0.0/16 subnetted with a /20 mask • 4094 host addresses per subnet • subnets ranging from 10.4.0.0/20 to 10.4.240.0/20

  28. VLSM These subnets could be subnetted further! All other /16 subnets are still available for use as /16 networks or to be subnetted.

  29. Hosts are assigned an IP address and mask from a specific subnet. VLSM What are the valid host IP Addresses? 10.2.1.55/24 10.2.5.55/24 All other /16 subnets are still available for use as /16 networks or to be subnetted. 10.255.0.5/16 10.4.0.55/20

  30. Host can only be a member of the subnet. Host can NOT be a member of the network that was subnetted. VLSM Are these valid host IP Addresses? YES! 10.2.1.55/24 10.2.0.55/16 NO! All other /16 subnets are still available for use as /16 networks or to be subnetted.

  31. VLSM 1 255.255.255.240 or /28

  32. VLSM 2 /30 – Gives 4 addresses - 2 usable host addresses

  33. VLSM 2 – Possible /30 options Conflicts Existing /27 Networks 1286432168421 .64 0 1 0 0 0 0 0 0 .96 0 1 1 0 0 0 0 0 .128 1 0 0 0 0 0 0 0 --------------------------------------- .113 0 1 1 1 0 0 0 1 .145 1 0 0 1 0 0 0 1 .193 1 1 00 0 0 0 1 Conflict Conflict /30 Choices Answer

  34. VLSM 2 – Our new VSLM Subnet Existing /27 Networks 1286432168421 .64 0 1 0 0 0 0 0 0 .96 0 1 1 0 0 0 0 0 .128 1 0 0 0 0 0 0 0 ---------------------------------------------- .192 1 1 00 0 0 0 0 (Net) .193 1 1 00 0 0 0 1 (1st hst) .194 1 1 00 0 0 1 0 (2nd hst) .195 1 1 00 0 0 1 1 (Bcast) .192 Network

  35. VLSM 2 – Other VLSM Subnets Existing /27 Networks .192 Network 1286432168421 .64 0 1 0 0 0 0 0 0 .96 0 1 1 0 0 0 0 0 .128 1 0 0 0 0 0 0 0 --------------------------------------- .192 1 1 00 0 0 0 0 .196 1 1 00 0 1 0 0 .200 1 1 00 1 0 0 0 .204 1 1 00 1 1 0 0 .208 1 1 01 0 0 0 0 .212 1 1 01 0 1 0 0 .216 1 1 01 1 0 0 0 .220 1 1 01 1 1 0 0 Other /30 Networks

  36. CIDR Route Summarization Calculating Route Summarization

  37. CIDR CIDR Report: www.cidr-report.org • CIDR allows routing protocols to summarize multiple networks, a block of addresses, as a single route. • An example is 172.16.1.0/24.

  38. Route Summarization • Route summarization (route aggregation) - Process of advertising a contiguous set of addresses as a single address with a less-specific, shorter subnet mask. • Remember that CIDR is a form of route summarization and is synonymous with the term…? • Supernetting.

  39. Route Summarization • CIDR ignores the limitation of classful boundaries and allows summarization with masks that are less than that of the default classful mask. • What type of routing protocols can propagate (distribute) supernets? • Classless routing protocols • Why? • Classless routing protocols include both the network address and the mask in the routing update. • Why can’t a classful routing protocol propagate supernets? • Classful routing protocols cannot include supernets in their routing updates because they cannot apply a mask less than the default classful mask.

  40. Route Summarization • For example, RIPv1 will summarize 172.30.0.0/24 subnets (172,30.1.0/24, 172.30.2.0/24 and 172.30.3.0/24) as 172.30.0.0. • R3 applies the /8 mask (classful routing protocol)

  41. Route Summarization • Why is this static route a supernet? • The /13 mask is less than the default Class B /16.

  42. More specific match? Different example from book. 172.16.0.0/16 172.16.10.0/24 S0/0/0 S0/0/1 • Could a router have both a specific route entry and a summary route entry covering the same network. • Yes • What if a packet with the destination IP address 172.16.10.10 entered this router? Where would it be forwarded and why? • The packet has a more specific (longer) match with 172.16.10.0/24, so S0/0/1 would be used to forward this packet. • A minimum of 24 bits match between the IP address and the route. • What is a packets with the destination IP address 172.16.20.10 entered this router? Where would it be forwarded and why? • The packet only has a match with the less specific172.16.10.0/24, so S0/0/1 would be used to forward this packet • A minimum of 16 bits match between the IP address and the route.

  43. Calculating Route Summarization • Calculating route summaries and supernets is identical to the process that you already learned in Chapter 2.

  44. Topics • Classful and Classless Addressing • Classful IP Addressing • Classful Routing Protocols • Classless IP Addressing • Classless Routing Protocols • VLSM • VLSM in Action • VLSM and IP Addresses • CIDR • Route Summarization • Calculating Route Summarization

  45. Chapter 6 VLSM and CIDR CIS 82 Routing Protocols and Concepts Rick Graziani Cabrillo College graziani@cabrillo.edu Last Updated: 2/24/2008

More Related