Today s Lecture I CLASSFUL IPv4 ADDRESSES DATAGRAM FORWARDING Internet Protocols IPv4 Addresses II Address Classes III Special Case Addresses IV Forwarding Basics CSC ECE 573 V Forwarding Decisions Fall 2005 VI Next Hop vs Destination Addresses N C State University copyright 2005 Douglas S Reeves 2 How Do Addresses Get Assigned 1 ICANN Internet Corp for Assigned Numbers and Names establishes policy for address and name allocation Allocates top level address space to regional registries IPv4 ADDRESSES 2 Regional registries allocate address space to ISPs companies and other organizations APNIC Asia Pacific ARIN North America RIPE Europe LACNIC Latin America and Caribbean 3 Sys admins assign individual host addresses copyright 2005 Douglas S Reeves IP Allocation Goals RFC 2050 4 How Do I Get to www ietf org 1 Conservation fair distribution of globally unique Internet address space no stockpiling 2 Routability distribution in a hierarchical manner makes routing easier User specifies destination of www ietf org DNS translates this to good bad 132 151 6 21 3 Public registries document address space allocation and assignment Router forwarding tables determine the path is some hops omitted 24 93 64 53 66 15 132 33 66 185 152 29 66 185 139 129 66 185 145 6 152 63 43 178 152 63 41 138 152 63 39 254 152 63 39 97 157 130 44 142 132 151 6 21 copyright 2005 Douglas S Reeves 5 copyright 2005 Douglas S Reeves 6 1 IPv4 Addresses Dotted Decimal Notation 32 bits long globally unique A convenient way to describe and remember IPv4 addresses Each interface has an IP address Example a router 32 bit address network A R IP1 IP5 8 bits Example Example a multi homed host IP1 8 bits 8 bits 10011000 00000001 00110110 00110000 Dotted decimal representation H 8 bits 152 1 54 48 IP2 network B copyright 2005 Douglas S Reeves copyright 2005 Douglas S Reeves 7 8 Classful Addresses Addresses are organized in a two level hierarchy 1 the network part leftmost most significant 2 the host part rightmost least significant IPv4 ADDRESS CLASSES x bits Network ID 32 x bits Host ID More networks larger network part means fewer hosts per network smaller host part and vice versa copyright 2005 Douglas S Reeves Classful Address Formats Class A 1 7 B 1 4 10 Network ID Host ID 2 1 Classes A addresses 0 0 0 0 127 255 255 255 8 110 Network ID Host ID B addresses 128 0 0 0 191 255 255 255 C addresses 192 0 0 0 223 255 225 225 2 8 1110 Multicast Address 5 E the first few bits of the address indicate this size 16 4 D The size number of bits in the network part is not fixed 24 3 C Classful Address Ranges 0 Network ID Host ID 2 10 D addresses 224 0 0 0 239 255 255 255 E addresses 240 0 0 0 255 255 255 2 7 11110 reserved copyright 2005 Douglas S Reeves 11 copyright 2005 Douglas S Reeves 12 2 Classful Network Sizes Class Example Why is class B address range 128 0 0 0 191 255 255 255 Potential Number Potential Number of of Networks Hosts Per Network Lowest possible address network and host parts class B A 27 128 224 16M B 214 16K 216 64K C 221 2M 28 256 10 000000 00000000 00000000 00000000 128 0 0 0 Highest possible address network and host parts class B 10 111111 11111111 11111111 11111111 128 copyright 2005 Douglas S Reeves 255 255 copyright 2005 Douglas S Reeves 13 Good or Bad 255 14 How Much of the Address Space is in Use 1 Good simple easy to understand 2 Bad limited address space 232 4G addresses not enough 3 Bad limited network size choices 3 ex what if a class C net needs to grow beyond 255 hosts 3 Bad moving to a new network requires changing IP addresses and may require updating DNS records copyright 2005 Douglas S Reeves copyright 2005 Douglas S Reeves 15 16 Network Addresses SPECIAL CASE IP ADDRESSES An IP address with host ID part 0 and network ID part all 0 s or all 1 s refers to the entire network network 128 10 0 0 interface 128 10 2 3 H interface 192 5 48 98 network 192 5 48 0 copyright 2005 Douglas S Reeves 18 3 Directed Broadcast Addresses Limited Broadcast Addresses An IP destination address with Host ID part all 1 s means all hosts attached to the specified network An IP destination address all 1 s means all hosts part of the same network as me Ex Packet sent to address 128 10 255 255 from host H5 will reach H1 H4 Ex Packet sent to 255 255 255 255 from host H3 reaches H1 H4 network 128 10 0 0 network 128 10 0 0 128 10 2 3 128 10 2 3 H1 128 10 2 5 H2 128 10 2 27 128 10 2 13 H3 H1 H4 128 10 2 5 H2 128 10 2 27 128 10 2 13 H3 H4 192 5 48 3 192 5 48 3 network 192 5 48 0 network 192 5 48 0 192 5 48 46 192 5 48 46 H5 H5 copyright 2005 Douglas S Reeves copyright 2005 Douglas S Reeves 19 Another Special Case 20 The Loopback Address An IP source address with network ID part all 0 s means from this network An IP destination address with network ID part all 1 s means this computer i e the one sending the packet Only allowed at startup during bootstrapping allows a machine to communicate temporarily before it learns its own IP address Used in testing network applications without sending data over a network ex ping 127 0 0 1 should always get a reply thereafter it must not use network 0 a datagram with destination address 127 x x x should never appear on any network copyright 2005 Douglas S Reeves Summary of Special Addresses For Address of Type If Network part is Anything other than all 0 s or all 1 s Destination Anything other than all 0 s or all 1 s And Host part is All 0 s 22 RFC 3330 Special Use IPv4 Addresses Then this means The address of the whole network All 1 s Broadcast address for the specified network All 1 s All 1 s Broadcast address for same network as originating host Source All 0 s Anything other than all 0 s or all 1 s host which doesn t yet know what network it is attached to Destination 127 Class A all 1 s Anything This computer source of the packet copyright 2005 Douglas S Reeves 23 Destination copyright 2005 Douglas S Reeves 21 0 0 0 0 0 255 255 255 This Network RFC1700 10 0 0 0 10 255 255 255 Private Use Networks RFC1918 24 0 0 0 24 255 255 255 Cable Television Networks 169 254 0 0 169 254 255 255 Link Local 172 16 0 0 172 23 255 255 Private Use Networks …