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Chapter 6 VLSM and CIDR

Chapter 6 VLSM and CIDR. TECI 185 Routing Protocols and Concepts Jack Yon Western Colorado Community College jyon@mesastate.edu Last Updated: 3/24/2009. Topics. Classful and Classless Addressing Classful IP Addressing Classful Routing Protocols Classless IP Addressing

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Chapter 6 VLSM and CIDR

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  1. Chapter 6 VLSM and CIDR TECI 185 Routing Protocols and Concepts Jack Yon Western Colorado Community College jyon@mesastate.edu Last Updated: 3/24/2009

  2. 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

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

  4. 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.

  5. 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)

  6. 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.

  7. 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

  8. 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)

  9. 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)

  10. 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

  11. 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

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

  13. 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

  14. 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.

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

  16. 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

  17. VLSM VLSM in Action VLSM and IP Addresses

  18. 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

  19. 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.

  20. 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.

  21. 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?

  22. 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.

  23. 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

  24. 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.

  25. 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

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

  27. 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

  28. 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.

  29. VLSM 1 255.255.255.240 or /28

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

  31. 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

  32. 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

  33. 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

  34. CIDR Route Summarization Calculating Route Summarization

  35. 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.

  36. 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.

  37. 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.

  38. 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)

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

  40. 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.

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

  42. 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

  43. Chapter 6 VLSM and CIDR TECI 185 Routing Protocols and Concepts Jack Yon Western Colorado Community College jyon@mesastate.edu Last Updated: 3/24/2008

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