1Internet Addresses (You should read Chapter 4 in Forouzan)IP Address is 32 Bits LongConceptually the address is the pair (NETID, HOSTID)Addresses are assigned by the internet company for assignment of names and numbersICANNICANN:Protocol Support Organization (PSO)Domain Name Supporting Organization (DNSO)Address Supporting Organization (ASO)Regional Internet RegistriesAmerican Registry for Internet Numbers (ARIN)http://www.arin.net/registration/fee_schedule.htmlwww.arin.netwww.icann.orgReference “ IP Fundamentals ” Chapter 1 and 2 by Maufer2Formats for IP addresses: (classful addressing)Class A0101101110Network (7 bits) Host (24 bits)Network (14 bits)Network (21 bits)Host (16 bits)Host (8 bits)Multicast address (28 bits)( There is a class E reserved for future use)Historically a class A address was assigned to networks with > 216 (65, 536) hostsClass B to networks with 28 (256) to 216 hostsClass C to networks with < 28 hostsClass BClass CClass D3Internet Addresses Cont.For Humans easier to deal with decimal so dotted decimal notation is used.Group 8 bits.8 bits.8 bits.8 bits and use decimal numbersExample 10000000 00001010 00000010 00011110 => 128.10.2.30Class Lowest Address Highest Address A 1.0.0.0 126.0.0.0 B 128.1.0.0 191.254.00 C 192. 0.1.0 223.255.254.0 D 224.0.0.0 239.255.255.255Some addresses are reservedExample 127.0.0.0 is reserved for loop back4IP version 4 uses 32 bit address 2 4.3 billion addresses32≈and 6.7 billion live on earth at presentClassless inter-domain routing (CIDR) discussed later slowed down addressexhaustion.Scaling Issues: 1. Eventual exhaustion of the IPV4 address space. 2. Ability to route traffic between ever increasing number of networks that comprise the internet.5IP addresses cont.Class A all 0’s network number is used to represent the “ default” route ( 0.0.0.0)this is a routing table entry which means any destination not matching any othertable entry should be sent to the default route. (more later)Class A all 1’s network number is loopback. 127.0.0.1 usually means “ This samemachine” all 127.anything.anything.anything is loopback.There are a total of 27 -2 = 126 class A networks.There are 214 - 2 = 16, 382 class B networks (again all 0’s & all 1’s networkaddresses reserved)There are 221-2 = 2,097,150 class C networks.There are 228 = 268, 435, 456 class D multicast addresses.6Notation:Class A has 8 bit network prefix this is called a slash 8’s /8can write 127.0.0.0 as 127/8 or 127.0.0.0/8/ 8 prefixes ( class A)Classful addressing allows using only the first 1,2,3 or 4 bits to determine theclass. (I.E. if MSB = 0 => class A/ 8 address block has 231 out of 232 total IP addresses=> / 8 takes up 50% total IPV4 addresses / 16 prefixes ( class B) 230total addresses => 25% total IPV4 addresses / 24 prefixes ( class C ) 229out of 232 => 12.5% total IPV4 addresses Class D with 1110 most significant bits used for multicastClass E with 1111 most significant bits and are reserved for experimental use7In the Beginning- IP addresses assigned based on request, not need- 32 bit address was thought to be plenty- classful addresses easy to understand and implement but not efficient / 24 supports 254 hosts too small / 16 supports 65,534 too large8IP RoutingFor a host IP routing is simple:If destination is directly connected to host then IP datagram is sent directly tothe destination.otherwise host sends datagram to a default routerThe IP layer can be configured to act as a router in addition to acting as a hostA host never forwards datagrams from one of its interfaces to another, while arouter forwards datagramsIP Layer has a routing table in memory that it searches each time it receives aa datagram to sendEach entry in routing table contains: - Destination IP address - IP address of a next hop router or IP address of a directly connected network - Flags (specify if network or host address) - Specification of which network interface the datagram should go to for transmission9IP Routing Performs The Following Actions:1. Search routing table for entry that matches complete destination IP address2. Search table for match of destination network IP. This check must take into account a possible “ Subnet Mask ” ( Defined Later ).3. Search for default entry.4. If none of the above discard and send host unreachable or network unreachable error back.Note: Hop by hop nature of this process.10Classical Subnetting Reference “ IP Fundamentals ” Chapter 3 Extended-Network-PrefixNetwork - Prefix Host - NumberNetwork - Prefix Subnet - Number Host - NumberBefore :After :Subnetting attacks the expanded routing table problem by making the subnetstructure of a network invisible outside the organization’s private network.External Internet Does Not Need To Know Internal Subnet Structure11Example : 172. 27. 0.0. / 16Subnet 1R A R CSubnet 2R BR DInternetSubnet 5Subnet 4Subnet 3R BR AInternet seesI need 5 subnets so I use 3 bits in the subnet - number field12This means I haveSubnet Number Binary representationof least-significant two bytesAvailable host addresseswithin each subnet0 172.27.0.0 00000000.00000000 0.1- 31. 2541 172.27.32.0 00100000.00000000 32.1- 63.2542 172.27.64.0 01000000.00000000 64.1- 95.2543 172.27.96.0 01100000.00000000 96.1-127.2544 172.27.128.0 10000000.00000000 128.1-159.2545 172.27.160.0 10100000.00000000 160.1-191.2546 172.27.192.0 11000000.00000000 192.1-223.2547 172.27.224.0 11100000.00000000 224.1-255.254Need a method to know how many bits are used for subnet-number=> subnet mask In this example the subnet mask is 255.255.224.0 11111111.11111111.11100000.0000000013Subnet MaskAt boot time a machine gets its own IP address ( stored on disk
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