Chapter 6 IPv4 Addresses – Part 2 CIS 81 Networking Fundamentals Rick Graziani Cabrillo College Last Updated: 3/30/2008

2 This Presentation For a copy of this presentation and access to my web site for other CCNA, CCNP, and Wireless resources please me for a username and password.   Web Site:

3 Note This presentation is not in the order of the book or online curriculum. This presentation also contains information beyond the curriculum.

Host IP Addresses

(net) (SM) (broadcast) (net) (SM) (broadcast)

6 Host IP Addresses … (broadcast) Number of hosts: 2 12 – 2 = 4,096 – 2 = 4,094 hosts

7 Who assigns IP Network Addresses? Internet Assigned Numbers Authority (IANA) ( is the master holder of the IP addresses. Today, the remaining IPv4 address space has been allocated to various other registries to manage for particular purposes or for regional areas.  Regional Internet Registries (RIRs)

8 Regional Internet Registries (RIR) The 5 RIR’s are:  AfriNIC (African Network Information Centre) - Africa Region  APNIC (Asia Pacific Network Information Centre) - Asia/Pacific Region  ARIN (American Registry for Internet Numbers) - North America Region  LACNIC (Regional Latin-American and Caribbean IP Address Registry) - Latin America and some Caribbean Islands  RIPE NCC (Reseaux IP Europeans) - Europe, the Middle East, and Central Asia

9 ISP (Internet Service Providers) Tier 1 ISP:  Large national or international ISPs that are directly connected to the Internet backbone.  Customers of Tier 1 ISPs:  lower-tiered ISPs  large companies and organizations.  Offer reliability and speed  AOL, SPRINT, Global Crossing, AT&T, Level 3, Verizon, NTT, Quest, SAVVIS Most companies or organizations obtain their IPv4 address blocks from an ISP.

10 ISP (Internet Service Providers) Tier 2 ISP:  Acquire their Internet service from Tier 1 ISPs. Tier 2 ISPs generally focus on business customers.  Examples: Allstream, AboveNet, British Telecom, Cogent Communications, France Telecom, Teleglobe TeliaSonera International Carrier Time Warner Telecom, Tiscali International Network, XO Communications Most companies or organizations obtain their IPv4 address blocks from an ISP.

11 ISP (Internet Service Providers) Tier 3 ISP:  Purchase their Internet service from Tier 2 ISPs. The focus of these ISPs is the retail and home markets in a specific locale. Examples:  Local ISPs Most companies or organizations obtain their IPv4 address blocks from an ISP.

12 Special Unicast IPv4 Addresses Default Route Loopback Address  Special address that hosts use to direct traffic to themselves.  to Link-Local Addresses  to ( /16)  Can be automatically assigned to the local host by the operating system in environments where no IP configuration is available. TEST-NET Addresses  to ( /24)  Set aside for teaching and learning purposes.  These addresses can be used in documentation and network examples.

13 Private IP Addresses RFC 1918  to ( /8)  to ( /12)  to ( /16) The addresses will not be routed in the Internet  Need NAT/PAT (next) Should be blocked by your ISP Allows for any network to have up to 16,777,216 hosts (/8)

14 Introducing NAT and PAT NAT is designed to conserve IP addresses and enable networks to use private IP addresses on internal networks. These private, internal addresses are translated to routable, public addresses. IPv4 addresses are almost depleted. NAT/PAT has allowed IPv4 to be the predominant network protocol, keeping IPv6 at-bay (for now).

15 NAT Example The translation from Private source IP address to Public source IP address

16 NAT Example Translation back, from Public destination IP address to Private destination IP address

17 PAT Example NAT/PAT table maintains translation of: DA, SA, SP 12

18 PAT Example 43 NAT/PAT table maintains translation of: SA (DA), DA (SA), DP (SP)

The Subnet Mask and the AND Operation

20 Subnet Mask The subnet mask is used to separate the network portion from the host portion of the address. On a host, the subnet mask tells the host what network it belongs to. Why does a host need to know what network it belongs to? Host: “I’m a host on the /24 network.”

21 Subnet Mask Why does a host need to know what network it belongs to? So, it knows whether to encapsulate the IP packet into an Ethernet frame with:  The Destination MAC Address of the default gateway  Must know the default gateway’s IP address  The Destination MAC Address of the host with the Destination IP address of the packet Later when we discuss Ethernet Host: “I’m a host on the /24 network.”

22 Subnet Mask Devices such as hosts use the bit-wise AND operation on the:  Host IP address  Subnet mask AND operation:  1 AND 1 = 1  0 AND anything = 0 Host IP: Mask: Net Add: NetworkHost

23 Subnet Mask AND operation:  1 AND 1 = 1  0 AND anything = 0 Host IP: Mask: Net Add: NetworkHost

24 Subnet Mask AND operation:  1 AND 1 = 1  0 AND anything = 0 Host IP: Mask: Net Add: NetworkHost

25 Subnet Masks: Non-Natural Boundaries Subnet masks do not have to end on natural octet boundaries … (broadcast) Number of hosts: 2 12 – 2 = 4,096 – 2 = 4,094 hosts

Subnetting: First Look

27 Subnets and Subnet Masks Formalized in 1985, the subnet mask breaks a single network in to smaller pieces. Allows network administrators to divide their network into small networks or subnets. Advantages will be discussed later.

28 What is subnetting? Subnetting is the process of borrowing bits from the HOST bits, in order to divide the larger network into small subnets. Subnetting does NOT give you more hosts, but actually costs you hosts. You lose two host IP Addresses for each subnet, one for the subnet IP address and one for the subnet broadcast IP address. You lose the last subnet and all of it’s hosts’ IP addresses as the broadcast for that subnet is the same as the broadcast for the network. In older technology, you would have lost the first subnet, as the subnet IP address is the same as the network IP address. (This subnet can be used in most networks.) Network Host Network SubnetHost

29 Analogy Before subnetting: In any network (or subnet) we can not use all the IP addresses for host addresses. We lose two addresses for every network or subnet. 1. Network Address - One address is reserved to that of the network. For Example: /16 2. Broadcast Address – One address is reserved to address all hosts in that network or subnet. For Example: This gives us a total of 65,534 usable hosts 98 Apples (100 – 2)

30 Analogy It is the same as taking a barrel of 100 apples and dividing it into 10 barrels of 10 apples each barrels x 10 apples = 100 apples 98 Apples (100 – 2)

31 However, in subnetting we will see that we lose two apples per subnet:  one for the network address  one for the broadcast address (less 2) barrels x 8 apples = 80 apples 2 = 1 network address + 1 broadcast address 98 Apples (100 – 2) (less 2)

32 In legacy networks, we also lost:  The first basket (subnet)  The network address of the first subnet is the network address of the entire network  The last basket (subnet)  The broadcast address for the last subnet is the same as for the entire network. (less 2) barrels x 8 apples = 64 apples 2 = 1 network address + 1 broadcast address 98 Apples (100 – 2) (less 2) X X

33 Subnet Example Network SubnetHost Network address with /16 Base Network Mask Using Subnets: Subnet Mask or / Etc Subnets 2 8 Subnets Addresses Subnet addresses: All 0’s in host portion

34 Subnet Example Network SubnetHosts Etc Each subnet has 254 hosts, 2 8 – Broadcast Network address with /16 Base Network Mask Using Subnets: Subnet Mask or /

35 With NO subnetting: NetworkFirst HostLast Host Broadcast ,534 host addresses, one for network address and one for broadcast address. Host IP Address:  A host of the /16 network Host IP Address:  A host of the /24 network

36 With subnetting: Network First Host Last Host Broadcast … Host IP Address:  A host of the /24 network

37 With subnetting: Network First Host Last Host Broadcast Hosts … ,024 Total address = 256 subnets * (256 hosts – 2) = 256 * 254 = 65,024 NOTE: It is common for some network administrator to not use the last subnet.

38 With subnetting: Network First Host Last Host Broadcast Major Network Address: Major Network Mask: Major Network Broadcast Address: Subnet Mask: First Subnet: Subnet Address: Subnet Broadcast Address: Last Subnet: Subnet Address: Subnet Broadcast Address:

Subnetting: Step-by-step

40 Determining Network and Subnet Information Use the Classless Subnetting Worksheet (Excel Spreadsheet) to do the following: Given any IP address and major network mask we can determine:  Major Network Address  First host address of the network  Last host address of the network  Broadcast address of the network  Number of usable hosts in the network If the network is subnetted and we know the subnet mask we can determine:  Subnet (network) Address  First host address of the subnet  Last host address of the subnet  Broadcast address of the subnet  Number of usable hosts in the subnet  Number of usable subnets in this network

41 See these spreadsheets on my website Worksheet: Classless Subnetting Worksheet (Excel spreadsheet) Nutshell: Classless Subnetting in a Nutshell (Excel spreadsheet)

42 Part 1: Determine Major Network Information

43 Convert IP Address/Network Mask to Binary First, let’s determine the Major Network Information. This is the information for the entire network, whether or not there are subnets. Using the Major Network Mask, determine the major network Address, the broadcast address for the entire network, and the number of hosts for the entire network. The Major Network Mask (or Base Mask, Subnet Mask) is provided by the ISP. Convert these addresses to binary. Host IP Address: Major Network Mask: (/16)

44 Determine Network Address Determine the Network Address by using the AND operation. Perform a bit-wise AND operation on the IP Address and the Subnet Mask Note: 1 AND 1 results in a 1, 0 AND anything results in a 0 Express the result in Dotted Decimal Notation The result is the Major Network Address of this for this host IP Address is

45 Determine Network Address A simple way of doing the AND operation: 1. In the Network mask locate where the 1’s end and the 0’s begin and draw a line. (I call this the “Major Network Divide” or “MD” on the worksheet.) 2. Now copy all of the bits above the 1 bits in the Network mask, to the Network address. 3. For the rest of the bits in the Network address (the bits below the 0’s in the Network mask) write all 0’s. Network PortionHost Portion Copy the bits from the Host IP Address to the Major Network Address Write all 0’s below the 0’s in the Major Network Mask MD

46 Network: Determine First Host, Last Host, Broadcast Addresses Remember that the network mask separates the network portion of the address from the host portion. Major Network Mask: or /16 The network address has all 0’s in the host portion of the address The broadcast address has all 1’s in the host portion of the address The first host is all 0’s and a 1 in the host portion of the address. The last host is all 1’s and a 0 in the host portion of the address. Network PortionHost Portion

47 Network: Determine First Host, Last Host, Broadcast Addresses The network address has all 0’s in the host portion of the address The broadcast address has all 1’s in the host portion of the address The first host is all 0’s and a 1 in the host portion of the address. The last host is all 1’s and a 0 in the host portion of the address. Network PortionHost Portion

48 Network: Determine the number of usable hosts By counting the number of host bits we can determine the total number of usable hosts for this network (before subnetting). Host bits: 16 Total number of hosts: 2 16 = 65,536 65,536 – 2 = 65,534 (Can’t use the all 0’s address, network address, or the all 1’s address, broadcast address.) Host Portion = 16 bits Network Portion

49 Part 2: Determine Subnet Information

50 Convert IP Address/Subnet Mask to Binary Now we will determine the Subnet Network Information. (Assuming we are subnetted.) This is the information only for that subnet. Using the Subnet Mask, determine the Subnet Address, the broadcast address for the entire network, and the number of hosts for the subnet. The Subnet Mask is determined by the network administrator, depending upon the number of subnets and the number of hosts per subnet that are needed. Convert these addresses to binary. Host IP Address: Subnet Mask: (/26)

51 Determine Subnet Address Determine the Network Address by using the AND operation. Perform a bit-wise AND operation on the IP Address and the Subnet Mask Note: 1 AND 1 results in a 1, 0 AND anything results in a 0 Express the result in Dotted Decimal Notation The result is the Major Network Address of this for this host IP Address is

52 Determine Subnet Address A simple way of doing the AND operation: 1. In the Subnet mask locate where the 1’s end and the 0’s begin and draw a line. (I call this the “Subnet Divide” or “SD” on the worksheet.) 2. Now copy all of the bits above the 1 bits in the Subnet mask, to the Network address. 3. For the rest of the bits in the Subnet address (the bits below the 0’s in the Network mask) write all 0’s. Network/Subnet PortionHost Portion Copy the bits from the Host IP Address to the Major Network Address Write all 0’s below the 0’s in the Major Network Mask SD

53 Subnet: Determine First Host, Last Host, Broadcast Addresses Remember that the network mask separates the network portion of the address from the host portion. Subnet Mask: or /26 The network address has all 0’s in the host portion of the address The broadcast address has all 1’s in the host portion of the address The first host is all 0’s and a 1 in the host portion of the address. The last host is all 1’s and a 0 in the host portion of the address. Network Portion Host Portion Subnet Portion

54 Subnet: Determine First Host, Last Host, Broadcast Addresses The subnet address has all 0’s in the host portion of the subnet address The broadcast address has all 1’s in the host portion of the subnet address The first host is all 0’s and a 1 in the host portion of the subnet address. The last host is all 1’s and a 0 in the host portion of the subnet address. Network Portion Host Portion Subnet Portion

55 Subnet: Determine the number of usable hosts By counting the number of host bits we can determine the total number of usable hosts for this subnet. Host bits: 6 Total number of hosts: 2 6 = – 2 = 62 (Can’t use the all 0’s address, network address, or the all 1’s address, broadcast address.) Network Portion Host Portion SD Subnet Portion

56 Subnet: Determine the number of usable subnets By counting the number of subnet bits we can determine the total number of usable hosts for this subnet. Subnet bits: 10 Total number of hosts: 2 10 = 1,024 1,024 – (0, 1, or 2) = ? 1,024 – 1 = 1,023 usable subnets The number of usable subnets depends upon whether or not we can use the first and/or last subnets. In today’s networks, both the first and last subnets are generally usable. In this example, the network administrator has determined the last subnet is not to be used. Network Portion Host Portion Subnet Portion SDMD

57 Overall Visual The subnet address has all 0’s in the host portion of the subnet address The broadcast address has all 1’s in the host portion of the subnet address The first host is all 0’s and a 1 in the host portion of the subnet address. The last host is all 1’s and a 0 in the host portion of the subnet address.

58 Overall Visual The following information must be provided: IP Address (host or network) Major Network Mask If subnetted: Subnet Mask Number of usable subnets (less 0, 1, or 2)

59 Notes Quick check First host: 1 more than network/subnet address Last host: 1 less than broadcast Does the host IP address fall in the range of network host addresses? Of subnet host addresses? How do hosts view the network? Hosts receive a host IP address and mask. Hosts only see themselves as part of their subnet (or network if not subnetted). They don’t know or care if they are in a network or subnet. Almost all networks are a subnet of some larger network.

60 See these spreadsheets on my website Worksheet: Classless Subnetting Worksheet (Excel spreadsheet) Nutshell: Classless Subnetting in a Nutshell (Excel spreadsheet)

61 Tips Use worksheets Don’t do short-cuts unless you understand the process we just discussed and you know what you are doing. Only use a subnet calculator to check your answers.  You must know how to subnet, then you can use the calculator.  Interviews, exams, and certification exams do not allow subnet calculators. Practice, practice, practice!

Chapter 6 IPv4 Addresses – Part 2 CIS 81 Networking Fundamentals Rick Graziani Cabrillo College Last Updated: 3/30/2008