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  • This chapter examines in detail the structure of IPv4 addresses and their application to the construction and testing of IP networks and subnetworks.
  • SubNet Mask AND Host Addr = Network (240 AND 148 = 144)
  • The allocation of these addresses inside the networks should be planned and documented.
  • There are benefits to using a layered model to describe network protocols and operations.
  • IPv6 features
  • Consider an internetwork that requires three subnets.
  • Consider this example with five LANs and a WAN for a total of 6 networks.
  • This scenario has the following requirements: AtlantaHQ 58 host addresses PerthHQ 26 host addresses SydneyHQ 10 host addresses CorpusHQ 10 host addresses WAN links 2 host addresses (each)
  • Given address block is 192.168.15.0/24.

Chapter6 Chapter6 Presentation Transcript

  • Ch 6 - Chapter 6 Addressing the Network – IPv4
  • Objectives
    • Explain the structure of IP addressing and demonstrate the ability to convert between 8-bit binary and decimal numbers
    • Given an IPv4 address, classify by type and describe how it is used in the network
    • Explain how addresses are assigned to networks by ISPs and within networks by administrators
    • Determine the network portion of the host address and explain the role of the subnet mask in dividing networks
    • Given IPv4 addressing information and design criteria, calculate the appropriate addressing components
    • Use common testing utilities to verify and test network connectivity and operational status of the IP protocol stack on a host
    Ch 6 -
  • IPv4 Addressing Structure
    • IPv4 is the current form of addressing used on the Internet
    • Uses the dotted decimal structure to represent the 32-bit IP address
    Ch 6 -
  • IP Address
    • Each device on a network must be uniquely defined
      • assigned a 32-bit address
      • used to identify the source and destination addresses
    • The 32-bit address is written in a dotted decimal format
      • each byte (or octet) is represented in decimal and separated by a dot
    • Contains the network and host portions
      • some portion of the higher-order bits represents the network address
      • the number of bits in the host portion determines the number of hosts within the network
    Ch 6 - network host
  • Decimal Numbering System
    • In the decimal numbering system, the radix (or base) is 10
      • has ten digits 0, 1, 2, 3, 4, 5, 6, 7, 8 and 9
    • 245 = (2 x 100) + (4 x 10) + (5 x 1)
    Ch 6 - 10 2 10 1 10 0 100 10 1 2 4 5 200 + 40 + 5 245
  • Binary Numbering System
    • In the binary numbering system, the radix (or base) is 2
      • has two digits 0 and 1
    • **11110101 = (1x128)+(1x64)+(1x32)+(1x16)+(0x8)+(1x4)+(0x2)+(1x1) = 245
    • Each octet has a minimum value of 0 and a maximum value of 255
    Ch 6 -
  • Binary Number Characteristics
    • The decimal value of any binary number is odd if the binary value of the least significant bit (LSB) is 1
    • The decimal value of any binary number is even if the binary value of the least significant bit (LSB) is 0
    Ch 6 - X = 0 or 1 128 64 32 16 8 4 2 1 X X X X X X X 0 even LSB 128 64 32 16 8 4 2 1 X X X X X X X 1 odd LSB
  • Binary to Decimal Conversion
    • Divide the 32 bits into 4 octets
    • Convert each octet to decimal
    • Add a “dot” between each decimal
    Ch 6 -
  • Decimal to Binary Conversion
    • Start by determining if the decimal number is equal to or greater than the largest decimal value represented by the most significant bit (MSB)
    Ch 6 -
  • Dotted Decimal to Binary Conversion
    • Separate and convert each decimal number separately
    • Arrange each octet into the 32-bit address
    Ch 6 -
  • Types of Address
    • Network address
      • a way to refer to the network as a whole
    • Broadcast address
      • a special address used to send packets to every hosts in the network that shares the same network portion of the address
    • Host address
      • each host in the network has a unique address
    Ch 6 -
  • Network Prefix
    • The prefix length is the number of bits in the address that gives the network (or subnetwork) portion
      • /25 is the prefix length that indicates the first 25 bits are the network address => Subnet Increment = 128
    Ch 6 -
  • 5 Shortcuts to Remember
    • /27=> 111 00000 – network portion , host portion
    • Subnet Increment => 0,32,64,96,128,160,192,224
    • Subnet Mask
    • 8 Subnet = 2 3 => 3 network bits
    • IP AND Mask = Subnet/Network
    Ch 6 - Increment 128 64 32 16 8 4 2 1 Subnet Bits 1 2 3 4 5 6 7 8 Mask 128 192 224 240 248 252 254 255 Subnet Bits 1 2 3 4 5 6 7 8
  • Calculating Network , Hosts and Broadcast Addresses
    • A network address contains all zeros in the host portion
    • The first useable host address has a 0 for each host bit except the last bit, which is a 1, in the host portion
    • The last useable host address has a 1 for each host bit except the
    Ch 6 -
    • last bit, which is a 0, in the host portion
    • The broadcast address contains all ones in the host portion
  • IP Address Example ( Popular Exam Question )
    • Last octet is 148 (10010100)
      • 1001 is part of the network portion (28=8+8+8+4)
      • 0100 is the host portion
    Ch 6 -
  • Unicast Transmission
    • The process of sending a packet from one host to another host
      • normal host-to-host communication
    • Unicast packets use the host address of the destination device as the destination address and can be routed through an internetwork
    Ch 6 -
  • Broadcast Transmission
    • The process of sending a packet from one host to all hosts in the network
      • packet uses a special broadcast address as the destination address
    • Used for locating special services/devices for which the address is not known or when the host needs to provide information to all hosts on the network
    Ch 6 -
      • mapping upper-layer addresses to lower-layer addresses
      • requesting an address
      • exchanging routing information by routing protocols
  • Broadcast Transmission (cont’d)
    • Directed broadcast
      • is sent to all hosts on a specific network , usually a non-local network
      • although routers do not forward directed broadcasts, they may be configured to do so
    • Limited broadcast
      • is used for communication that is limited to hosts on the local network
      • packets used a destination address of 255.255.255.255 (all ones)
      • packets addressed to the limited broadcast address will only appear on the local network
    Ch 6 -
  • Multicast Transmission
    • The process of sending a packet from one host to a selected group of hosts
      • designed to conserve bandwidth
    • A special block of addresses from 224.0.0.0 to 239.255.255.255 is used for multicast groups addressing
    Ch 6 -
    • Hosts that wish to receive particular multicast data are called multicast clients
      • video and audio distribution
      • routing information exchange by routing protocols
      • software distribution
      • news feeds
  • Reserved IPv4 Address
    • IPv4 address range is from 0.0.0.0 to 255.255.255.255
      • not all these addresses can be used for host addresses in unicast transmission
    • Multicast and experimental addresses are reserved for special purposes
    Ch 6 -
  • Public and Private Addresses
    • Public addresses
      • designated for use in networks that are accessible on the Internet
    • Private addresses
      • blocks of addresses that are used in private networks that require no or limited Internet access
    Ch 6 -
  • Private Addresses
    • Three blocks of IP address space for private networks
    • (online assessment question)
      • 10.0.0.0 to 10.255.255.255 (10.0.0.0/8)
      • 172.16.0.0 to 172.31.255.255 (172.16.0.0/12)
      • 192.168.0.0 to 192.168.255.255 (192.168.0.0/16)
    • Routers do not have routes to forward private address to the appropriate private networks
    • Routers can use a service, called network address translation (NAT), to translate private addresses to public addresses
      • NAT allows the hosts in a private network to “borrow” a public address for communicating to outside networks
    Ch 6 -
  • Special IPv4 Addresses
    • Network and broadcast addresses
      • the first, network, and last, broadcast, addresses cannot be assigned to hosts within each network
    • Default route ( 0.0.0.0 /8)
      • used as a “catch all” route when a more specific route is NOT available
    • Loopback address( 127.0.0.1 )
      • a special address that hosts use to direct traffic to themselves
      • entire address block, 127.0.0.0 to 127.255.255.255, is reserved
    • Link-local addresses (Routers will not forward packets with link-local addresses)
      • 169.254.0.0 to 169.254.255.255 (169.254.0.0/16)
      • addresses are assigned to the local host by the operating system in environments where no IP configuration is available
      • used in a small peer-to-peer network or for a host that could not automatically obtain an address from a DHCP server
      • a host must not send an IPv4 link-local destination address to any router for forwarding and should set the TTL for these packets to 1
    Ch 6 -
  • Special IPv4 Addresses (cont’d)
    • TEST-NET address (Routers will not forward packets with TEST-NET addresses)
      • address block 192.0.2.0 to 192.0.2.255 is reserved for teaching and learning purposes
    Ch 6 -
  • IP Address Classes
    • Class A address
      • designed to support very large networks with more than 16 million hosts
      • first octet has a value of 1 to 126
      • used a fixed /8 prefix with the first octet to indicate the network address
      • remaining three octets are used for host addresses
    • Class B address
      • designed to support the needs of moderate to large size networks with more than 65,000 hosts
      • first octet has a value of 128 to 191
      • first and second octets represent the network
    • Class C address ( 192 to 223 )
      • intended to provide addresses for small networks with a maximum of 254 hosts
    Ch 6 -
  • IP Address Classes (cont’d)
      • first octet has a value of 192 to 223
      • first three octets represent the network
    Ch 6 -
  • Address Planning and Documentation
    • Preventing duplication of address
      • each host in an internetwork must have a unique address
      • could assign a same address to more than one hosts
    • Providing and controlling access
      • access to resources , such as servers, can be controlled using Layer 3 address
      • blocking access to a random address assignment for a server is difficult and client may not locate this resource
    • Monitoring security and performance
      • examine network traffic looking for addresses that are generating or receiving excessive packets
    Ch 6 -
  • Using Private Addresses
    • Will there be more devices connected to the network than public addresses allocated by the ISP?
    • Will the devices need to be accessed from outside the local network?
    • If the devices that may be assigned private addresses require to access the Internet, is this network capable of providing a NAT service?
    Ch 6 -
  • Static Addressing for End Devices
    • A network administrator must manually configure the network information for a host
    • Static assignment of address can provide increased control of network resources
      • time consuming to enter the information on each host
    Ch 6 -
      • necessary to maintain an accurate list of address for each device to prevent address duplication
  • Dynamic Addressing for End Devices
    • Preferred method of assigning IP addresses to hosts on large networks using DHCP
      • address is leased for a period of time
      • reduces the burden of support staff
      • eliminates entry errors
    Ch 6 -
  • Assigning Addresses to Other Devices
    • Addresses for servers and peripherals eg: Printer
      • should have a static address
      • servers and peripherals are concentration points for network traffic
    • Addresses for hosts that are accessible from Internet
      • the addresses for these devices should be static
      • must have a public space address associated with it
    • Addresses for intermediary devices, eg: Router, Switch
      • intermediary devices are also a concentration point for network traffic
      • may be used as hosts to configure, monitor, or troubleshoot network operation
      • addresses are assigned manually to these devices
    Ch 6 -
  • Assigning Addresses to Other Devices (cont’d)
    • Routers and firewalls
      • each interface is assigned an address manually
      • these devices are used for packet filtering
    Ch 6 -
  • IP Address Allocation
    • Internet Assigned Numbers Authority ( IANA )
      • master holder of the IP address
      • IP multicast and IPv6 are obtained directly from IANA
    • Regional Internet Registries (RIR)
      • remaining IPv4 address space is managed by RIR since mid 1990s
    Ch 6 -
  • Internet Service Providers ( ISP s) (Eg: Starhub, Singtel)
    • Role
      • supply a small number of useable IPv4 addresses (6 or 14) to their customers as part of their services
    • Services
      • DNS services, e-mail services and website
    • Tiers
      • Tier 1 ISPs provide reliability and speed with multiple connections to the Internet backbone
      • Tier 2 ISPs generally focus on business customers
      • Tier 3 ISPs focus on the retail and home market in a specific locale
    Ch 6 -
  • ISP Tiers Ch 6 -
  • IPv6 Overview
    • Improved packet handling
    • Increased scalability and longevity
    • QoS mechanisms
    • Integrated security
    Ch 6 -
  • IPv6 Capabilities
    • 128-bit hierarchical addressing
      • to expand addressing capabilities
    • Header format simplification (online assessment question)
      • to improve packet handling
    • Improved support for extensions and options
      • for increased scalability, longevity and improved packet handling
    • Flow labeling capabilities
      • QoS mechanism
    • Authentication and privacy capabilities
      • to integrate security
    Ch 6 -
  • Subnet Mask
    • The prefix and subnet mask are different ways of representing the same thing – the network portion of an IP address
    Ch 6 -
  • Subnet Mask Template Ch 6 - 128 64 32 16 8 4 2 1 Address bits 128 192 224 240 248 252 254 255 Possible Subnet Address 1 1 1 1 1 1 1 1
  • The AND Operation
    • A host address is logically AND ed with its subnet mask to determine the network address to which the host is associated
    • Routers use ANDing to determine an acceptable route for an incoming packet
      • the destination network address is compared to the routes from the routing table
    Ch 6 -
    • An originating host must determine if a packet should be sent directly to a host in a local network or be directed to the gateway
  • The ANDing Process
    • Convert host address to binary
    • Convert prefix to binary subnet mask
    • AND each bit of host address with corresponding bit of mask
    • Convert binary network address to decimal
    Ch 6 -
    • 1 AND 1 = 1
    • 0 AND 1 = 0
    • 1 AND 0 = 0
    • 0 AND 0 = 0
  • Basic Subnetting
    • Subnetting allows for creating multiple logical networks from a single address block
    • Subnets are created using one or more of the host bits as network bits
      • done by extending the mask to borrow some of the bits from the host portion to create additional network bits
    Ch 6 -
  • Calculating Subnets and Hosts
    • The number of subnets is calculated using 2 n , where n is the number of bits borrowed
      • 2 1 = 2 subnets
      • the more bits borrowed, the more subnets can be defined
    • The number of useable hosts per subnet is calculated using 2 h - 2 where h is the number of host bits left
      • 2 7 – 2 = 126 useable hosts per subnet
      • with each bit borrowed, fewer host addresses are available per subnet
    Ch 6 -
  • Subnetting Example 1
    • Need to borrow a minimum of 2 host bits to cater for 3 subnets
      • 2 2 = 4 subnets
    Ch 6 -
  • Subnetting Example 1 (cont’d)
    • 6 host bits are left in the last octet
    • 2 6 – 2 = 62 hosts per subnet
    Ch 6 -
  • Subnetting Example 2
    • Need to borrow a minimum of 3 host bits to cater for 6 subnets
      • 2 3 = 8 subnets
    Ch 6 -
  • Subnetting Example 2 (cont’d)
    • 5 host bits are left in the last octet
    • 2 5 – 2 = 30 hosts per subnet
    Ch 6 -
  • Fixed Length Subnet Mask (FLSM)
    • Using traditional subnetting or FLSM, each subnet is allocated the same number of host addresses
      • these fixed size address block would be efficient if all subnets have the same requirements for the number of hosts
    Ch 6 - 2 5 – 2 = 30 hosts per subnet
  • Variable Length Subnet Mask ( VLSM )
    • VLSM was designed to maximize addressing efficiency
      • each WAN link requires 2 host addresses
    • Breaks up a subnet into a smaller subnet
    Ch 6 -
  • Using FLSM
    • Standard subnetting would lock each subnet into blocks of 62 hosts
      • 2 6 – 2 = 62 hosts to meet the highest number of hosts required
    Ch 6 -
  • Using FLSM (cont’d)
    • The network has a given address block of 192.168.15.0/24
    • Need 6 host bits to support the largest user requirement
    • The unused addresses are especially evident when the LAN routers support 10 users only
    • Each WAN link has 60 unused address
    Ch 6 -
  • Using VLSM – Step 1
    • Calculate a subnet from the original 192.168.15.0/24 block to accommodate the largest LAN, i.e. 58 hosts
    • Keep 6 host bits to cater for the 58 hosts
      • 2 6 – 2 = 62 useable host addresses
      • mask for last octet 11000000
    • 2 bits are borrowed to create 4 possible subnets
      • 192.168.15.0/26 (subnet 0)
      • 192.168.15.64/26 (subnet 1)
      • 192.168.15.128/26 (subnet 2)
      • 192.168.15.192/26 (subnet 3)
    • Assign subnet 0 (192.168.15.0/26) to this LAN
      • 3 subnets left unused
    Ch 6 -
  • Using VLSM – Step 2
    • Consider the LAN with the next fewer hosts, i.e. 26 hosts
    • Require 5 host bits to accommodate 26 hosts
      • 2 5 – 2 = 30 useable host addresses
      • mask for the last octet is 11100000
    • Use the next available address of 192.168.15.64/26 to create an address block for this subnet
    • One more bit is borrowed from the above subnet
      • 192.168.15.64/27
    • This subnet, 192.168.15.64/27, creates two more subnets
      • 192.168.15.01000000/27 (subnet 0)  192.168.15.64/27
      • 192.168.15.01100000/27 (subnet 1)  192.168.15.96/27
    • Assign the 192.168.15.64/27 to this LAN
      • 1 subnet left unused
    Ch 6 -
  • Using VLSM – Step 3
    • Consider the LAN with the next fewer hosts, i.e. 10 hosts
    • Require 4 host bits to accommodate 10 hosts
      • 2 4 – 2 = 14 useable host addresses
      • mask for the last octet is 11110000
    • Use the next available address of 192.168.15.96/27 to create an address block for this subnet
    • One more bit is borrowed from the above subnet
      • 192.168.15.96/28
    • This subnet, 192.168.15.96/28, creates two more subnets
      • 192.168.15.01100000/28 (subnet 0)  192.168.15.96/28
      • 192.168.15.01110000/28 (subnet 1)  192.168.15.112/28
    • Assign both these subnets to the LANs with the same number of hosts
      • no subnet left
    Ch 6 -
  • Using VLSM – Step 4
    • Point-to-point WAN links require two host addresses
    • Require two host bits to provide two host addresses
      • 2 2 – 2 = 2 useable host addresses
      • mask for the last octet is 11111100
    • Use the next available address of 192.168.15.128/26 to create an address block for this subnet
    • Four more bits are borrowed from the above subnet
      • 192.168.15.128/30
    • This subnet, 192.168.15.128/30, creates 16 more subnets
      • 192.168.15.10000000/30 (subnet 0)  192.168.15.128/30
      • 192.168.15.10000100/30 (subnet 1)  192.168.15.132/30
      • 192.168.15.10001000/30 (subnet 2)  192.168.15.136/30
      • 192.168.15.10001100/30 (subnet 3)  192.168.15.140/30
    Ch 6 -
  • Using VLSM – Step 5
    • Calculate the address range and broadcast address for each subnet
    • Document the host requirements, subnet addresses, address range, broadcast addresses and network prefix
    Ch 6 -
  • Using VLSM – Network Diagram Ch 6 -
  • Testing Connectivity
    • Ping is a utility for testing IP connectivity between hosts
      • sends out requests for responses from a specified host address
      • provides a display output with a summary of the responses including the success rate and average round-trip time
      • uses Internet Control Message Protocol ( ICMP ), a Layer 3 protocol (Network)
    • Source device sends an ICMP echo request datagram to the destination device
      • destination device responds with an ICMP echo reply if it receives the echo request
      • ping measures the time taken for the reply
    Ch 6 - echo request echo reply source destination
  • Testing Local TCP/IP Stack Ch 6 -
  • Testing Connectivity to Local Gateway
    • Test the host’s connectivity to the router interface
    • Verify the correct address is configured as the default gateway
    Ch 6 -
    • Security applied to the router interface may prevent it from responding to echo requests
  • Testing Connectivity to Remote LAN
    • The ping command can also be used to verify the availability or reachability of a remote device
    • Lack of ping response could be due to security restrictions and not because of non-operational elements of the network
    Ch 6 -
  • Testing The Path
    • Traceroute , or tracert , is a utility to observe the path between two hosts
    • The trace generates a list of hops that were successfully reached along the path
      • if the data reaches the destination, the trace lists the interface on every router in the path
      • if the data fails at some hop along the way, the trace lists the address of the last router that responded
    • An asterisk (*) is used to indicate a lost packet
    • Traceroute makes use of the TTL field
      • the initial value in the TTL field in the first message is set to 1, allowing a single hop to the first router
      • traceroute then progressively increments the TTL field for each message until the destination is reached
    Ch 6 -
  • ICMP
    • IP uses the services of ICMP to send messages in the event of certain errors
      • ICMP messages provide feedback about issues related to the processing of IP packets under certain conditions
      • ICMP messages are not intended to make IP reliable
    • ICMP provides control and error messages
      • host confirmation – echo request and echo reply
      • unreachable destination or service
      • time exceeded
      • route redirection
      • source quench
    • ICMP messages are often not allowed for security reasons
    Ch 6 -