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Lecture CCNA Exploration 4.0 (Kỳ 2) - Chapter 6: VLSM and CIDR

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This chapter compare and contrast classful and classless IP addressing, review VLSM and explain the benefits of classless IP addressing, describe the role of the Classless Inter-Domain Routing (CIDR) standard in making efficient use of scarce IPv4 addresses.

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Nội dung Text: Lecture CCNA Exploration 4.0 (Kỳ 2) - Chapter 6: VLSM and CIDR

  1. Chapter 6: VLSM and CIDR CCNA Exploration version 4.0
  2. Objectives • Compare and contrast classful and classless IP addressing. • Review VLSM and explain the benefits of classless IP addressing. • Describe the role of the Classless Inter-Domain Routing (CIDR) standard in making efficient use of scarce IPv4 addresses Học viện mạng Bách Khoa - Website: www.bkacad.com 2
  3. Introduction • Prior to 1981, IP addresses used only the first 8 bits to specify the network portion of the address • In 1981, RFC 791 modified the IPv4 32-bit address to allow for three different classes • IP address space was depleting rapidly – The Internet Engineering Task Force (IETF) introduced Classless Inter-Domain Routing (CIDR) – CIDR uses Variable Length Subnet Masking (VLSM) to help conserve address space. 1. VLSM is simply subnetting a subnet 2. Subnets can be further subnetted in multiple levels 3. In addition to subnetting, it became possible to summarize a large collection of classful networks into an aggregate route, or supernet. Học viện mạng Bách Khoa - Website: www.bkacad.com 3
  4. Classful and Classless Addressing Học viện mạng Bách Khoa - Website: www.bkacad.com 4
  5. Classful IP Addressing • As of January 2007, there are over 433 million hosts on internet Học viện mạng Bách Khoa - Website: www.bkacad.com 5
  6. Classful IP Addressing • Initiatives to conserve IPv4 address space include: 1. VLSM & CIDR notation (1993, RFC 1519) 2. Network Address Translation (1994, RFC 1631) 3. Private Addressing (1996, RFC 1918) Học viện mạng Bách Khoa - Website: www.bkacad.com 6
  7. Classful IP Addressing Học viện mạng Bách Khoa - Website: www.bkacad.com 7
  8. Classful IP Addressing • Classes of IP addresses are identified by the decimal number of the 1st octet – Class A address begin with a 0 bit • Range of class A addresses 0.0.0.0 to 127.255.255.255 – Class B address begin with a 1 bit and a 0 bit • Range of class B addresses 128.0.0.0 to 191.255.255.255 – Class C addresses begin with two 1 bits & a 0 bit • Range of class C addresses 192.0.0.0 to 223.255.255.255 Học viện mạng Bách Khoa - Website: www.bkacad.com 8
  9. Classful IP Addressing • The IPv4 Classful Addressing Structure (RFC 790) • An IP address has 2 parts: – The network portion: the left side of an IP address – The host portion: the right side of an IP address Học viện mạng Bách Khoa - Website: www.bkacad.com 9
  10. Classful IP Addressing Học viện mạng Bách Khoa - Website: www.bkacad.com 10
  11. Classful Routing Protocol Học viện mạng Bách Khoa - Website: www.bkacad.com 11
  12. Classful Routing Protocol • Recall that classful routing protocols (i.e. RIPv1) do not send subnet masks in their routing updates – Router receives the routing update could determine the subnet mask simply by examining the value of the first octet in the network address, or by applying its ingress interface mask for subnetted routes. – The reason is that the Subnet mask is directly related to the network address Học viện mạng Bách Khoa - Website: www.bkacad.com 12
  13. Classful Routing Protocol • Convergence ? R1 R2 Học viện mạng Bách Khoa - Website: www.bkacad.com 13
  14. Extra: The problems of IP v4 1. Exhaustion of the Class B network address space. One fundamental cause of this problem is the lack of a network class of a size that is appropriate for mid-sized organization. • Class C is too small, whereas Class B is too large for most organizations but was the best fit available for use with subnetting. 2. Growth of routing tables in Internet routers beyond the ability of current software, hardware, and people to effectively manage. 3. Eventual exhaustion of the 32-bit IPv4 address space. Học viện mạng Bách Khoa - Website: www.bkacad.com 14
  15. Extra: The problems of IP v4 • The design and deployment of CIDR was intended to solve these problems by providing a mechanism to slow the growth of global routing tables and to reduce the rate of consumption of IPv4 address space. • It did not and does not attempt to solve the third problem. • http://tools.ietf.org/rfc/rfc4632.txt Học viện mạng Bách Khoa - Website: www.bkacad.com 15
  16. Classless IP Addressing • Classless Inter-domain Routing (CIDR – RFC 1517). Allows for: – More efficient use of IPv4 address space – Prefix aggregation, which reduced the size of routing tables (route summarization ) • Requires subnet mask to be included in routing update because address class is meaningless Học viện mạng Bách Khoa - Website: www.bkacad.com 16
  17. CIDR and Route Summarization • CIDR uses Variable Length Subnet Masks (VLSM) to allocate IP addresses to subnets according to individual need rather than by class. Học viện mạng Bách Khoa - Website: www.bkacad.com 17
  18. CIDR and Route Summarization • CIDR allowed for prefix aggregation, which you already know as route summarization. • A supernet summarizes multiple network addresses with a mask less than the classful mask. • 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. Học viện mạng Bách Khoa - Website: www.bkacad.com 18
  19. CIDR and Route Summarization Học viện mạng Bách Khoa - Website: www.bkacad.com 19
  20. Classless Routing Protocol • Characteristics of classless routing protocols: –Routing updates include the subnet mask –Supports VLSM –Supports Route Summarization Học viện mạng Bách Khoa - Website: www.bkacad.com 20
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