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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 4 subnets? • 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 4 subnets? • What would the Mask be? • 255.255.255.192 (/26) • What would the addresses of each subnet be? • 172.16.1.0/26 • 172.16.1.64/26 • 172.16.1.128/26 • 172.16.1.192/26 • What would the range of hosts be for each subnet? • 172.16.1.0/26: 172.16.1.1-172.16.1.62 • 172.16.1.64/26: 172.16.1.65-172.16.1.126 • 172.16.1.128/26: 172.16.1.129-172.16.1.191 • 172.16.1.192/26: 172.16.1.193-172.16.1.254

  18. 16 /30 subnets VLSM – Using the chart Still have 3 /26 subnets • What if we needed several (four) /30 subnets for our serial links? • Take one of the /26 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. Background • That short-term solution was Network Address Translation (NAT) and RFC 1918. • There are two fundamental drivers behind the growing recognition of the need for IPv6. (NAT stifles innovation in these areas.) • New applications using core concepts such as: • mobile IP • service quality guarantees • end-to-end security • peer-to-peer networking. • Rapid modernization of heavily populated countries such as India and China. • A compelling statistic is that the number of remaining unallocated IPv4 addresses is almost the same as the population of China: about 1.3 billion.

  43. IPv6 • IPv6 replaces the 32-bit IPv4 address with a 128-bit address, making 340 trillion trillion trillion IP addresses available. 340,282,366,920,938,463,463,374,607,431,768,211,456 addresses • Represented by breaking them up into eight 16-bit segments. • Each segment is written in hexadecimal between 0x0000 and 0xFFFF, separated by colons. • An example of a written IPv6 address is 3ffe:1944:0100:000a:0000:00bc:2500:0d0b

  44. 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.

  45. Global Unicast Addresses • The host portion of the address is called the Interface ID. • The reason for this name is that a host can have more than one IPv6 interface, and so the address more correctly identifies an interface on a host than a host itself. • But that subtlety only goes so far: • A single interface can have: • multiple IPv6 addresses, and • an IPv4 address in addition.

  46. Global Unicast Addresses • Subnet Identifier is part of the network portion of the address rather than the host portion. • A big benefit is that the Interface ID can be a consistent size for all IPv6 addresses. • And making the Subnet ID a part of the network portion creates a clear separation of functions: • The network portion provides the location of a device down to the specific data link and • the host portion provides the identity of the device on the data link.

  47. Global Unicast Addresses • With very few exceptions: • Interface ID is 64 bits • Subnet ID field is 16 bits • provides for 65,536 separate subnets • The IANA and the Regional Internet Registries (RIRs) assign IPv6 prefixes—normally /32 or /35 in length—to the Local Internet Registries (LIRs). • The LIRs, which are usually large Internet Service Providers, then allocate longer prefixes to their customers. In the majority of cases, the prefixes assigned by the LIRs are /48.

  48. Background • IPv4 will exist for some time, as the transition begins to IPv6. • Other new protocols have been developed in support of IPv6: • Routing protocols (OSPFv3) so routers can learn about IPv6 network addresses. • ICMPv6

  49. ICMP: Ping and Trace

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