The Internet Protocol IP John Kristoff jtk depaul edu 1 312 362 5878 DePaul University Chicago IL 60604 TDC 375 Winter 2002 John Kristoff DePaul University 1 Will layer 2 networking suffice TDC 375 Winter 2002 John Kristoff DePaul University 1 Layer 3 usually provides Internetworking for data link technologies Globally unique addresses Scalable routing A common communications format Packet fragmentation capability A hardware independent interface Packet independence TDC 375 Winter 2002 John Kristoff DePaul University 1 An IP Router or gateway Usually a special purpose dedicated device Connects heterogenous networks Directs packets toward ultimate destination Dynamic routing algorithms often used They make automatic forwarding decisions They can forward based on various metrics Official pronounciation is really rooter Layer 3 switch router layer 3 switch TDC 375 Winter 2002 John Kristoff DePaul University 1 IP Routing Scope Dynamic routing Protocol for route exchange and computation Static routing Autonomous system interior exterior Manually configured routes Destination address driven TDC 375 Winter 2002 John Kristoff DePaul University 1 Internet protocol IP Standardized in RFC 791 Connectionless Unreliable Fairly simple The Internet Glue TDC 375 Winter 2002 John Kristoff DePaul University 1 IP addresses Virtual not bound to hardware 32 bit fixed size Unique address for each IP interface Global authories assign a prefix network Local administrators assign the suffix host Usually written as dotted decimal notation e g 140 192 1 6 TDC 375 Winter 2002 John Kristoff DePaul University 1 IP address types Unicast one to one Multicast one to many Receivers join listen to multicast group address Broadcast one to all Source address should always be unicast Special case of a multicast usually best avoided Anycast one to one of many Preferably one to nearest defined for IPv6 TDC 375 Winter 2002 John Kristoff DePaul University 1 IP address notation TDC 375 Winter 2002 John Kristoff DePaul University 1 Special IP addresses TDC 375 Winter 2002 John Kristoff DePaul University 1 Classful IP addressing TDC 375 Winter 2002 John Kristoff DePaul University 1 Classful address sizes TDC 375 Winter 2002 John Kristoff DePaul University 1 Example IP network TDC 375 Winter 2002 John Kristoff DePaul University 1 Example IP router addressing TDC 375 Winter 2002 John Kristoff DePaul University 1 Limitations of classful addressing Internet growth Route table size Address depletion Misappropriation of addresses Lack of support for different sized networks Class B too big class C too small TDC 375 Winter 2002 John Kristoff DePaul University 1 IP addressing solutions Subnetting Supernetting Classless interdomain routing CIDR Variable length subnet masks VLSM TDC 375 Winter 2002 John Kristoff DePaul University 1 Subnetting TDC 375 Winter 2002 John Kristoff DePaul University 1 Subnet mask The bit length of the prefix network Prefix network is no longer classful Dotted decimal or notation 140 192 1 6 s subnet mask is 255 255 255 128 or 140 192 1 6 25 You may want to convert to binary for clarity A 25 or 255 255 255 128 subnet mask is 11111111 11111111 11111111 10000000 TDC 375 Winter 2002 John Kristoff DePaul University 1 Example Using subnet masks Given 140 192 50 8 20 what is the subnet mask in dotted decimal notation directed broadcast address in dotted decimal total number of hosts that can be addressed TDC 375 Winter 2002 John Kristoff DePaul University 1 Supernetting Combine smaller blocks into larger aggregate If class B too big class C too small Maybe do this Combine 199 63 0 0 24 to 199 63 15 0 24 Equals 199 63 0 0 20 TDC 375 Winter 2002 John Kristoff DePaul University 1 Example Using Supernets Given that ISP has 128 15 0 0 16 If a customer needs to address 300 hosts how might the ISP assign them address space What is the address space assigned in the example above in slash notation How many if any maximum free IP addresses will the customer have at their disposal Can you think of any reason why the customer might have less than that maximum TDC 375 Winter 2002 John Kristoff DePaul University 1 CIDR Use supernetting for routing tables Routes advertised as smaller CIDR blocks So instead of advertising Advertise 199 5 6 0 24 199 5 6 1 24 199 5 6 2 24 and 199 5 6 1 24 separately 199 5 6 0 22 one time Internet CIDR report http www employees org tbates cidr report html TDC 375 Winter 2002 John Kristoff DePaul University 1 Example Using CIDR Given that an ISP announces netblocks 64 5 0 0 20 64 5 16 0 20 192 0 2 0 25 and 192 0 2 192 26 and 192 0 2 128 26 What is the smallest number of CIDR announcements that this ISP can make If these routes are received from another provider can you think of any reason why they might not be able to be CIDR ized TDC 375 Winter 2002 John Kristoff DePaul University 1 VLSM Multiple subnet sizes in a single AS Allows efficient use of address space Can be used to build internal hierarchy External view of AS does not change An organization may have 140 192 0 0 16 But internally may use 140 192 0 0 17 140 192 128 0 24 140 192 129 0 24 and so on TDC 375 Winter 2002 John Kristoff DePaul University 1 Example Using VLSM Given an address space of 140 192 0 0 16 to work with assign netblocks and addresses based on the following network 6 satellite sites and 1 main office center About 7000 hosts exist on entire network today Main site uses approximately 50 of addresses Satellites vary from 200 to 700 total addresses Overall growth for organization is 500 hosts year TDC 375 Winter 2002 John Kristoff DePaul University 1 Obtaining IP addresses IANA has global authority for assignment Regional registries delegate ARIN RIPE APNIC ISPs assign addresses to end end users RFC 1918 defines private address netblocks NOT globally unique Must not appear on the public Internet 10 0 0 0 8 172 16 0 0 12 192 168 0 0 16 TDC 375 Winter 2002 John Kristoff DePaul University 1 IP datagram layout TDC 375 Winter 2002 John Kristoff DePaul University 1 Inside an IPv4 datagram Version field Header length Binary 0100 equals what in decimal Length of the IP header in 32 bit words Will usually be equal 5 in decimal Type of Service now DiffServ field An indication of quality class of service Rarely used but if so usually within single AS TDC 375 Winter 2002 John Kristoff DePaul University 1 Inside an IPv4 datagram cont Total length Identification Total IP datagram length in octets Maximum value is 65535 but rarely 1500