Chapter 6 Notes

Chapter 6 Addressing the Network – IPv4  The Anatomy of an IPv4 Address ➢ IPv4 Addresses  At network layer, packets of the comm. Need to be identified with source & dest. Addresses of the 2 end systems  Each packet has a 32-bit source address & 32-bit dest. Address in Layer 3 header.  IPv4 addresses represented using dotted decimal system • Each octet separated by a dot  Network – a group of hosts that have identical bit patterns in the network address portion of their addresses  Number of bits used in the host portion determines # of hosts we can have within the network ➢ Decimal to Binary  Most Significant Bit – highest bit value in binary (leftmost bit)  Addressing for Different Purposes ➢ Types of Addresses in an IPv4 Network  Network address – the address by which we refer to the network • The lowest address is reserved for the network address  Broadcast address – a special address used to send data to all hosts in the network • Uses highest address in the network range • Used to send packets to every host in the network that shares the same network portion of the address  Host address – the addresses assigned to the end devices in the network • Each host has a unique address  Network Prefixes • The number of bits in the address that gives us the network portion ➢ Types of Communication  Unicast – the process of sending a packet from one host to an individual host • client/server and peer-to-peer  Broadcast – sending a packet from one host to all hosts on the network • Generally restricted to local network • Host receives as it would a unicast packet • Used for location of special services/devices for which the address is not known • Host requests = queries • Local network restriction based on config. of router • 2 Types of broadcast ♦ Directed broadcast ➢ Sent to all hosts on a specific network ♦ Limited Broadcast ➢ Used for communication that is limited to the hosts on the local network

Multicast – sending a packet from one host to a selected group of hosts • Local network or routed through internetwork • Conserve bandwidth • One packet sent to multiple hosts • Multicast Clients – hosts that wish to receive particular multicast data, subscribe to ♦ Multicast group • When subscribed to, host processes packets addressed to this multicast address, as well as packets addressed to its uniquely allocated unicast address • Multicast address range subdivided into different types of addresses ♦ Reserved link local addresses ➢ IP address in the range from 169.254.1.0 to 169.254.254.255 ➢ Used to auto. Assign an IP address to a device in an IP network when there is no other assignment method available (DHCP Server) ♦ Globally scoped addressees ➢ Unique addresses that are public domain addresses ♦ Administratively scoped addresses (limited scope addresses) ➢ Restricted to a local group or organization • 224.0.0.0 to 224.0.0.255 – reserved link local addresses ♦ Packets transmitted with a TTL value of 1 ♦ Router should never forward ♦ Typical usage is in routing protocols using multicast trans. to exchange routing info. ➢ Public and Private Addresses  Private • 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) • Hosts that do not require access to the Internet at large may make unrestricted use of Private networks • Router/firewall at perimeter of network blocks private packets from going to ISP  NAT (Network Address Translation) – translation of private addresses to public domain addresses  Public • Majority of IPv4 unicast host range ➢ Special Addresses  Network & Broadcast  Default Route – 0.0.0.0 • “catch all” route when more specific route is not avail. • Reserves 0.0.0.0 – 0.255.255.255 (0.0.0.0 /8) address block  Loopback – 127.0.0.1 • Special address that hosts use to direct traffic to themselves • Ping address to test config. of TCP/IP on local host 

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• 127.0.0.0 – 127.255.255.255 reserved Link-Local Addresses – 169.254.0.0 – 169.254.255.255 • Can be automatically assigned to the local host by the OS in environments where no IP config. is available ♦ Small P2P network for a host that could not automatically obtain address from DHCP server • Only suitable within same network • A host must not send a packet with an IPv4 link-local dest. Address to any router for forwarding ♦ Set TTL to 1

TEST-NET – 192.0.2.0 – 192.0.2.255 (192.0.2.0 /24) • Teaching and learning purposes • Network devices will accept these addresses in their configurations ➢ Legacy IPv4 Addressing  Class A Blocks (1-127) • Extremely large networks (>16 million hosts) • Fixed /8 prefix • Remaining 3 octets used for host address ♦ Only 128 possible Class A networks (0.0.0.0 /8 – 127.0.0.0 /8)  Class B Blocks (128-191) • Moderate to large size networks (>65,000 hosts) • Used two high-order octets to indicate network address ♦ Other two specified host • Most significant two bits of the high-order octet were 10 ♦ Restricted from 128.0.0.0 /16 to 191.255.0.0 /16 • More efficiency than Class A  Class C Blocks (192-223) • Most commonly available • Maximum of 254 hosts • /24 prefix ♦ Used only last octet as host address ♦ First three – network address • Fixed value of 110 for the three most significant bits of high-order octet ♦ Restricted 192.0.0.0 /16 to 223.255.255.0 /16 • 2 million networks  Limits to the Class-based System • Classful allocation of address space often wasted many addresses, which exhausted the availability of IPv4 addressing • System abandoned in the late 1990s ♦ Computer still determines class & makes appropriate subnet mask assignment  Classless addressing • IPv4 addressing scheme that uses a subnet mask that does not follow classful addressing rules 

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Provides increased flexibility when dividing ranges of IP addresses into separate networks • System we currently use • Address blocks appropriate to the # of hosts are assigned to companies without regard to the unicast class  Assigning Addresses  Allocation of network layer address space within network needs to be well designed  Admins should not randomly select addresses used / address assignment within be random  Allocation of addresses should be planed for purpose of: • Preventing duplication of addresses • Providing and controlling access • Monitoring security and performance ➢ Monitoring Security and Performance  Examine network traffic looking for addresses generating / receiving excessive packets  Identify device on the network that has a problematic address ➢ Assigning Addresses within a Network  Different types of hosts • End devices for users • Servers and peripherals • Hosts that are accessible from the Internet • Intermediary devices  Each diff. dev. Types should be allocated to a logical block of addresses within the address range of the network ➢ Static or Dynamic Addressing for End User Devices  Static • Network admin must manually configure the network information for a host ♦ Entering host IP address, subnet mask, default gateway • Useful for printers, servers and other devices that need to be accessible to clients on network • Can provide increased control of network resources • Time-consuming  Dynamic • Using Dynamic Host Configuration Protocol (DHCP) • Automatic assignment of IP address, subnet mask, default gateway & other info. • Requires a block of addresses (address pool) be defined to be assigned to DHCP clients • Preferred method • Addresses not permanent, “leased” for period of time ♦ When host is powered down, address is released into pool for reuse ➢ Assigning Addresses to Other Devices  Addresses for hosts that are Accessible from Internet

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Usually servers Address should be static Each server must have a public space address associated with it ♦ Variations in the address of one dev. Will make dev. Inaccessible from the Internet • Private networks – ♦ Router / firewall at perimeter of the network must be configured to translate the internal address into a public address  Addresses for Intermediary Devices • Almost all traffic within or between networks passes through some form of intermediary device ♦ Network devices provide great location for network management, monitoring & security • Most int. devices Layer 3 • Hubs, switches & wireless access pts do not require IPv4 add. to operate as int. dev. ♦ Need addresses assigned if accessed as hosts • should be in a different range within the network block than user device addresses  Routers and Firewalls • IPv4 address assigned to each interface • Concentration point of traffic entering & leaving network • Major role in security ♦ Filtering packets based on source &/ dest. IPv4 addresses  Devices IP Address Ranges ➢ ISPs  ISP Tiers – ISPs are designated by a hierarchy based on level of connectivity to Internet Backbone  Internet Backbone – a high-speed line or serios of connections that forms a major pathway within a network • Tier 1 ISPs ♦ Directly connect to Internet Backbone ♦ Highly reliable connections & services ♦ Primary advantages for customers: reliability & speed • Tier 2 ISPs ♦ Acquire internet service from Tier 1 ISPs ♦ Focus on business customers ♦ Serve Tier 3 ISPs ♦ Have IT resources to operate own services – DNS, e-mail servers, web servers ♦ Slower & lower reliability than Tier 1 • Tier 3 ISPs ♦ Internet from Tier 2 ISPs ♦ Retail & home markets ➢ IPv6  Expanded addressing capabilities

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• Improved packet handling • Increased scalability and longevity • QoS mechanisms • Integrated security IPv6 Offers: • 128-bit hierarchical addressing ♦ Expand addressing capabilities ♦ Expressed as 8 hexadecimal values, separated by colons • Header format simplification ♦ Improve packet handling • Improved support for extensions & options ♦ Increased scalability/longevity & improved packet handling • Flow labeling capability ♦ As QoS mechanisms • Authentication and privacy capabilities ♦ Integrate security New Protocol suite • New messaging protocol (ICMPv6) • New routing protocols

 Is It On My Network? ➢ The Subnet Mask – Defining the Network and Host Portions  32-bit pattern  Represented by • Binary 1 in each network position bit • Binary 0 in each host position bit  Prefix and subnet mask are different ways of representing the same thing – network portion  If submask is represented by 255 • All equivalent bits in that octet of address are network bits  If submask is represented by 0 • All equiv. bits in that octet of address are host bits ➢ ANDing – between host address & subnet mask gives network address  Reasons to use AND • Routers use ANDing to determine an acceptable route for an incoming packet • Originating host must determine if a packet should be sent directly to a host in the local network or be directed to the gateway ➢ Subnetting  Calculating Subnets • 2^n; n = number of bits borrowed  Number of Hosts • 2^n – 2; n = number of bits left for hosts  Dividing Networks into Right Sizes • Determine the Number and Size of the Networks

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Consider size required based on common groupings of hosts Address planning in a network diagram ♦ Allows us to see the networks and make a more accurate count • Plan carefully to ensure address blocks assigned to subnet do not overlap ➢ Subnetting a Subnet  6.5.3.1