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Chapter 6 IPv4 Addresses – Part 3

Chapter 6 IPv4 Addresses – Part 3. CIS 81 Networking Fundamentals Rick Graziani Cabrillo College graziani@cabrillo.edu Last Updated: 4/13/2008. Topics. Calculating the number subnets/hosts needed VLSM (Variable Length Subnet Masks) Classful Subnetting IPv6 ICMP: Ping and Traceroute.

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Chapter 6 IPv4 Addresses – Part 3

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  1. Chapter 6IPv4 Addresses – Part 3 CIS 81 Networking Fundamentals Rick Graziani Cabrillo College graziani@cabrillo.edu Last Updated: 4/13/2008

  2. Topics • Calculating the number subnets/hosts needed • VLSM (Variable Length Subnet Masks) • Classful Subnetting • IPv6 • ICMP: Ping and Traceroute

  3. Calculating the number subnets/hosts needed

  4. Calculating the number subnets/hosts needed 172.16.1.0 255.255.255.0 Network Host • Network 172.16.1.0/24 • Need: • As many subnets as possible, 60 hosts per subnet

  5. Calculating the number subnets/hosts needed Number of hosts per subnet 172.16.1. 0 0 0 0 0 0 0 0 255.255.255. 0 0 0 0 0 0 0 0 • Network 172.16.1.0/24 • Need: • As many subnets as possible, 60 hosts per subnet 6 host bits Network Host

  6. Calculating the number subnets/hosts needed Number of subnets 172.16.1. 0 0 0 0 0 0 0 0 255.255.255. 1 1 0 0 0 0 0 0 255.255.255.192 • Network 172.16.1.0/24 • Need: • As many subnets as possible, 60 hosts per subnet • New Subnet Mask: 255.255.255.192 (/26) • Number of Hosts per subnet: 6 bits, 64-2 hosts, 62 hosts • Number of Subnets: 2 bits or 4 subnets 6 host bits Network Host

  7. Calculating the number subnets/hosts needed 172.16.1.0 255.255.255.0 Network Host • Network 172.16.1.0/24 • Need: • As many subnets as possible, 12 hosts per subnet

  8. Calculating the number subnets/hosts needed Number of hosts per subnet 172.16.1. 0 0 0 0 0 0 0 0 255.255.255. 0 0 0 0 0 0 0 0 • Network 172.16.1.0/24 • Need: • As many subnets as possible, 12 hosts per subnet 4 host bits Network Host

  9. Calculating the number subnets/hosts needed Number of hosts per subnet Number of subnets 172.16.1. 0 0 0 0 0 0 0 0 255.255.255. 1 11 1 0 0 0 0 255.255.255.240 • Network 172.16.1.0/24 • Need: • As many subnets as possible, 12 hosts per subnet • New Subnet Mask: 255.255.255.240 (/28) • Number of Hosts per subnet: 4 bits, 16-2 hosts, 14 hosts • Number of Subnets: 4 bits or 16 subnets 4 host bits Network Host

  10. Calculating the number subnets/hosts needed 172.16.1.0 255.255.255.0 Network Host • Network 172.16.1.0/24 • Need: • Need 6 subnets, as many hosts per subnet as possible

  11. Calculating the number subnets/hosts needed Number of subnets 172.16.1. 0 0 0 0 0 0 0 0 255.255.255. 0 0 0 0 0 0 0 0 • Network 172.16.1.0/24 • Need: • Need 6 subnets, as many hosts per subnet as possible 3 subnet bits Network Host

  12. Calculating the number subnets/hosts needed Number of hosts per subnet Number of subnets 172.16.1. 0 0 0 0 0 0 0 0 255.255.255. 1 1 10 0 0 0 0 255.255.255.224 • Network 172.16.1.0/24 • Need: • Need 6 subnets, as many hosts per subnet as possible • New Subnet Mask: 255.255.255.224 (/27) • Number of Hosts per subnet: 5 bits, 32-2 hosts, 30 hosts • Number of Subnets: 3 bits or 8 subnets 3 subnet bits Network Host

  13. VLSM (Variable Length Subnet Masks)

  14. VLSM • If you know how to subnet, you can do VLSM. • Example: 10.0.0.0/8 • Subnet in /16 subnets: • 10.0.0.0/16 • 10.1.0.0/16 • 10.2.0.0/16 • 10.3.0.0/16 • Etc. • Subnet one of the subnets (10.1.0.0/16) • 10.1.0.0/24 • 10.1.1.0/24 • 10.1.2.0/24 • 10.1.3.0/24 • etc

  15. Host can only be a member of the subnet. Host can NOT be a member of the network that was subnetted. VLSM YES! 10.2.1.55/24 10.2.1.55/16 NO! All other /16 subnets are still available for use as /16 networks or to be subnetted.

  16. VLSM – Using the chart • This chart can be used to help determine subnet addresses. • This can any octet. • We’ll keep it simple and make it the fourth octet. • Network: 172.16.1.0/24 • What if we needed 10 subnets with a minimum of 12 hosts? • What would the Mask be? • What would the addresses of each subnet be? • What would the range of hosts be for each subnet?

  17. VLSM – Using the chart • Network: 172.16.1.0/24 • What if we needed 5 subnets? • What would the Mask be? • 255.255.255.240 (/28) • What would the addresses of each subnet be? • 172.16.1.0/28 • 172.16.1.32/28 • 172.16.1.64/28 • 172.16.1.96/28 • 172.16.1.128/28 • 172.16.1.160/28 • 172.16.1.192/28 • 172.16.1.224/28 • What would the range of valid hosts for each subnet? • 172.16.1.0/26: 172.16.1.1-172.16.1.31 • 172.16.1.32/26: 172.16.1.33-172.16.1.62 • 172.16.1.64/26: 172.16.1.65-172.16.1.94 • 172.16.1.96/26: 172.16.1.97-172.16.1.126 • Etc.

  18. 16 /30 subnets VLSM – Using the chart Still have 7 /27 subnets • What if we needed several (four) /30 subnets for our serial links? • Take one of the /27 subnets and subnet it again into /30 subnets. 16 /30 subnets

  19. Classful Subnetting

  20. Classful IP Addressing • In the early days of the Internet, IP addresses were allocated to organizations based on request rather than actual need. • When an organization received an IP network address, that address was associated with a “Class”, A, B, or C. • This is known as Classful IP Addressing • The first octet of the address determined what class the network belonged to and which bits were the network bits and which bits were the host bits. • There were no subnet masks. • It was not until 1992 when the IETF introduced CIDR (Classless Interdomain Routing), making the address class meaning less. • This is known as Classless IP Addressing. • For now, all you need to know is that today’s networks are classless, except for some things like the structure of Cisco’s IP routing table and for those networks that still use Classful routing protocols. • You will learn more about this is CIS 82, CIS 83 and CIS 185.

  21. IPv4 Address Classes

  22. Address Classes 1st octet 2nd octet 3rd octet 4th octet Class A Network Host Host Host Class B Network Network Host Host Class C Network Network Network Host N = Network number assigned by ARIN (American Registry for Internet Numbers) H = Host number assigned by administrator

  23. Network Host Host Host 8 bits 8 bits 8 bits Default Mask: 255.0.0.0 (/8) Class A addresses First octet is between 0 – 127, begins with 0 With 24 bits available for hosts, there a 224 possible addresses. That’s 16,777,216 nodes! Number between 0 - 127 • There are 126 class A addresses. • 0 and 127 have special meaning and are not used. • 16,777,214 host addresses, one for network address and one for broadcast address. • Only large organizations such as the military, government agencies, universities, and large corporations have class A addresses. • For example ISPs have 24.0.0.0 and 63.0.0.0 • Class A addresses account for 2,147,483,648 of the possible IPv4 addresses. • That’s 50 % of the total unicast address space, if classful was still used in the Internet!

  24. 8 bits 8 bits Default Mask: 255.255.0.0 (/16) Class B addresses First octet is between 128 – 191, begins with 10 Network Network Host Host With 16 bits available for hosts, there a 216 possible addresses. That’s 65,536 nodes! Number between 128 - 191 • There are 16,384 (214) class B networks. • 65,534 host addresses, one for network address and one for broadcast address. • Class B addresses represent 25% of the total IPv4 unicast address space. • Class B addresses are assigned to large organizations including corporations (such as Cisco, government agencies, and school districts).

  25. 8 bits Default Mask: 255.255.255.0 (/24) Class C addresses First octet is between 192 – 223, begins with 110 Network Network Network Host With 8 bits available for hosts, there a 28 possible addresses. That’s 256 nodes! Number between 192 - 223 • There are 2,097,152 possible class C networks. • 254 host addresses, one for network address and one for broadcast address. • Class C addresses represent 12.5% of the total IPv4 unicast address space.

  26. IPv4 Address Classes • No medium size host networks • In the early days of the Internet, IP addresses were allocated to organizations based on request rather than actual need.

  27. Network based on first octet • The network portion of the IP address was dependent upon the first octet. • There was no “Base Network Mask” provided by the ISP. • The network mask was inherent in the address itself.

  28. IPv4 Address Classes Class D Addresses • A Class D address begins with binary 1110 in the first octet. • First octet range 224 to 239. • Class D address can be used to represent a group of hosts called a host group, or multicast group. Class E AddressesFirst octet of an IP address begins with 1111 • Class E addresses are reserved for experimental purposes and should not be used for addressing hosts or multicast groups. 

  29. Fill in the information… 1. 192.168.1.3 Class _____ Default Mask:______________ Network: _________________ Broadcast: ________________ Hosts: _________________ through ___________________ 2. 1.12.100.31 Class ______ Default Mask:______________ Network: _________________ Broadcast: ________________ Hosts: _________________ through _____________________ 3. 172.30.77.5 Class ______ Default Mask:______________ Network: _________________ Broadcast: ________________ Hosts: _________________ through _____________________

  30. Fill in the information… 1. 192.168.1.3 Class C Default Mask: 255.255.255.0 Network: 192.168.1.0 Broadcast: 192.168.1.255 Hosts: 192.168.1.1 through 192.168.1.254 2. 1.12.100.31 Class A Default Mask: 255.0.0.0 Network: 1.0.0.0 Broadcast: 1.255.255.255 Hosts: 1.0.0.1 through 1.255.255.254 3. 172.30.77.5 Class B Default Mask: 255.255.0.0 Network: 172.30.0.0 Broadcast: 172.30.255.255 Hosts: 172.30.0.1. through 172.30.255.254

  31. Class separates network from host bits • The Class determines the Base Network Mask! 1. 192.168.1.3 Class C Default Mask: 255.255.255.0 Network: 192.168.1.0 2. 1.12.100.31 Class A Default Mask: 255.0.0.0 Network: 1.0.0.0 3. 172.30.77.5 Class B Default Mask: 255.255.0.0 Network: 172.30.0.0

  32. Know the classes! First First Network Host ClassBitsOctetBitsBits A 0 0 – 127 8 24 B 10 128 - 191 16 16 C 110 192 - 223 24 8 D 1110 224 – 239 E 1111 240 - 255

  33. IP addressing crisis • Address Depletion • Internet Routing Table Explosion

  34. IPv4 Addressing Subnet Mask • One solution to the IP address shortage was thought to be the subnet mask. • Formalized in 1985 (RFC 950), the subnet mask breaks a single class A, B or C network in to smaller pieces. • This does allow a network administrator to divide their network into subnets. • Routers still associated an network address with the first octet of the IP address.

  35. All Zeros and All Ones Subnets Using the All Ones Subnet • There is no command to enable or disable the use of the all-ones subnet, it is enabled by default. Router(config)#ip subnet-zero • The use of the all-ones subnet has always been explicitly allowed and the use of subnet zero is explicitly allowed since Cisco IOS version 12.0. RFC 1878 states, "This practice (of excluding all-zeros and all-ones subnets) is obsolete! Modern software will be able to utilize all definable networks." Today, the use of subnet zero and the all-ones subnet is generally accepted and most vendors support their use, though, on certain networks, particularly the ones using legacy software, the use of subnet zero and the all-ones subnet can lead to problems. CCO: Subnet Zero and the All-Ones Subnethttp://www.cisco.com/en/US/tech/tk648/tk361/technologies_tech_note09186a0080093f18.shtml

  36. Long Term Solution: IPv6 (coming) • IPv6, or IPng (IP – the Next Generation) uses a 128-bit address space, yielding 340,282,366,920,938,463,463,374,607,431,768,211,456 possible addresses. • IPv6 has been slow to arrive • IPv6 requires new software; IT staffs must be retrained • IPv6 will most likely coexist with IPv4 for years to come. • Some experts believe IPv4 will remain for more than 10 years.

  37. Short Term Solutions: IPv4 Enhancements Discussed in CIS 83 and CIS 185 • CIDR (Classless Inter-Domain Routing) – RFCs 1517, 1518, 1519, 1520 • VLSM (Variable Length Subnet Mask) – RFC 1009 • Private Addressing - RFC 1918 • NAT/PAT (Network Address Translation / Port Address Translation) – RFC • More later when we discuss TCP

  38. ISPs no longer restricted to three classes. Can now allocate a large range of network addresses based on customer requirements 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”

  39. Active BGP entries – March, 2006 http://bgp.potaroo.net/

  40. ISP/NAP Hierarchy - “The Internet: Still hierarchical after all these years.” Jeff Doyle (Tries to be anyways!)

  41. IPv6

  42. Why Do We Need a Larger Address Space? • Internet population • Approximately 973 million users in November 2005 • Emerging population and geopolitical and address space • Mobile users • PDA, pen-tablet, notepad, and so on • Approximately 20 million in 2004 • Mobile phones • Already 1 billion mobile phones delivered by the industry • Transportation • 1 billion automobiles forecast for 2008 • Internet access in planes – Example: Lufthansa • Consumer devices • Sony mandated that all its products be IPv6-enabled by 2005 • Billions of home and industrial appliances

  43. IP Address Allocation History 1981, IPv4 Protocol was published. 1985, 1/16 of IPv4 address space in use. 2001, 2/3 of IPv4 address space in use.

  44. Larger Address Space IPv4 • 32 bits or 4 bytes long 4,200,000,000 possible addressable nodes IPv6 • 128 bits or 16 bytes: four times the bits of IPv4 3.4 * 1038 possible addressable nodes 340,282,366,920,938,463,374,607,432,768,211,456 5 * 1028 addresses per person 50,000,000,000,000,000,000,000,000,000

  45. Larger Address Space Enables Address Aggregation • Aggregation of prefixes announced in the global routing table • Efficient and scalable routing

  46. IPv6 • Address assignment features: Using DHCP and Stateless Autoconfiguration. • Built-in Support for Mobility: IPv6 supports mobility such that IPv6 hosts can move around the Internetwork, retain their IPv6 address and without losing current application sessions. • Aggregation: IPv6’s huge address space makes for much easier aggregation of blocks of addresses in the Internet, making routing in the Internet more efficient. • No need for NAT/PAT: The huge public IPv6 address space removes the need for NAT/PAT, which avoids some NAT-induced application problems and makes for more efficient routing. • No Broadcasts: IPv6 does not use layer 3 broadcast addresses, instead relying on multicasts to reach multiple hosts. • Transition tools: IPv6 has many rich tools to help with the transition from IPv4 to IPv6.

  47. Three types of IPv6 Addresses The three types of IPv6 address follow: • Unicast • Global Unicast • Link Local Unicast • Unique Local Unicast • Multicast • Anycast • Unlike IPv4, there is no IPv6 broadcast address. • There is, however, an "all nodes" multicast address, which serves essentially the same purpose as a broadcast address.

  48. Unicast Addresses • A unicast address is an address that identifies a single device. • A global unicast address is a unicast address that is globally unique. • Has global scope. • Globally unique and can therefore be routed globally with no modification.

  49. Global Unicast Addresses Replaced with • Note: This format, specified in RFC 3587, obsoletes and simplifies an earlier format that divided the IPv6 unicast address into Top Level Aggregator (TLA), Next-Level Aggregator (NLA), and other fields. However, you should be aware that this obsolescence is relatively recent and you are likely to encounter some books and documents that show the old IPv6 address format.

  50. Unicast Addresses • The host portion of the address is called the Interface ID. • Host can have more than one IPv6 interface • Address more correctly identifies an interface on a host than a host itself. • A single interface can have multiple IPv6 addresses, and can have an IPv4 address in addition.

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