Addressing in TCP/IP LESSON 6 (September 22, 1995) Daniel Z. Tabor Jr. New Jersey Institute of Technology Lesson 6 - (1 of 37) Outline: Addressing in TCP/IP • A Need for Identification • Internet Address Classification • Network and Host ID Ranges • Addresses Specify Network Connections • Network and Broadcast Addresses • Multicast Addresses • Weaknesses in IP Addresses • Common Representation of Addresses • Loopback Addresses • Obtaining an IP Address • Contacting the NIC • Network Byte Ordering • Mapping Names to IP Addresses Lesson 6 - (2 of 37) A Need for Identification: • There is a need to establish: – A globally accepted method of identifying computers. – To provide a universal communication service. Lesson 6 - (3 of 37) A Need for Identification: • TCP/IP universal host identifiers - are standard compact binary addresses used for efficient computation in routing and identification. – Scheme is analogous to physical network addressing where: • Each host on the internet is assigned an integer address (IP address) of 32-bits. • That address is represented in “dotted-decimal” notation. Lesson 6 - (4 of 37) A Need for Identification: – Each address is a conceptual pair of (netid, hostid) • netid: identifies a network • hostid: identifies a host on that network. Lesson 6 - (5 of 37) Internet Address Classification: • IP Addresses (version 4) – Five classes (A,B,C,D,E) – They are distinguished by their first 5 bits. – Addresses are 32-bits. • Later versions of the Internet Protocol may have more classes and use a different number of bits to represent an address. – IPv6 (proposed) uses 64-bits. Lesson 6 - (6 of 37) Internet Address Classification: • Class E - (11110) - Reserved for future use. • Class D - (1110) - Multicast addressing. – Currently being used with applications that use selective broadcasting in communication: • Video-conferencing. • MBONE • Audio-conferencing. Lesson 6 - (7 of 37) Internet Address Classification: • The three highest-order bits are used to determine the three Primary Classes: • Class A - (0) - used for a handful of networks which have more than 65,536 (216) hosts attached to each. – Netid = 7 bits – Hostid = 24 bits – Ex. (10.0.0.1) - ARPANET Lesson 6 - (8 of 37) Internet Address Classification: • Class B - (10) - used for intermediate size networks that have between 256 (28) and 65,536 (216) hosts attached to each. – Netid = 14 bits – Hostid = 16 bits – Ex. (128.235.251.11) - Hertz.njit.edu Lesson 6 - (9 of 37) Internet Address Classification: • Class C - (110) smallest configuration for hosts. Allows for less than 256 (28) hosts attached to each. – Netid = 21 bits – Hostid = 8 bits – Ex. (195.213.49.3) - Local area networks • Addresses are designed to allow extraction of either id quickly which makes gateway routing more efficient. Lesson 6 - (10 of 37) IPv4 Address Types: Class A 0 1 2 3 4 netid 0 Class B 1 0 Class C 1 1 0 Class D 1 1 1 0 Class E 1 1 1 0 8 16 24 31 hostid netid hostid netid hostid multicast address reserved for future use 1 Lesson 6 - (11 of 37) Network and Host ID Ranges: Address Class A Class B Class C Class D Network Range Host Range 0.0.0.0 - 127.0.0.0 0.0.0 - 255.255.255 128.0.0.0 - 191.255.0.0 0.0 - 255.255 192.0.0.0 - 223.255.255.0 0 - 255 224.0.0.0 - 239.255.255.255 N/A Lesson 6 - (12 of 37) Addresses Specify Network Connections: • Gateways connect two or more physical networks. Each connection requires its own IP address. • Conventional computers that have two or more physical connections are called multi-homed hosts and require multiple IP addresses. • IP addresses specify both a network and a host on that network (not an individual machine, but its connection to the network). Lesson 6 - (13 of 37) Network and Broadcast Addresses: • Hostid = 0 (128.235.0.0) : names/addresses the network as a whole. (Ex. NJIT network) • Hostid = All 1’s (128.235.255.255) : directed broadcast address which refers to every host on that network. (Ex. Hertz.njit.edu) • Netid & Hostid = All 1’s (255.255.255.255) : limited broadcast address provides broadcast address independent of assigned Netid. Lesson 6 - (14 of 37) Network and Broadcast Addresses: • Directed broadcast addresses require knowledge of the network address, limited broadcast addresses do not. • Limited broadcast addresses provide a broadcast address for local networks, independent of the assigned Netid. Lesson 6 - (15 of 37) Network and Broadcast Addresses: Notations • 1’s => ‘All’ • 0’s => ‘This’ • Netid = 0 => ‘This network’ Lesson 6 - (16 of 37) Multicast Addresses: • Multicast addresses - provide multi-point delivery of packets. • Also known as selective broadcasting, multicast addressing is a subset of normal broadcasting. • Multicast addresses can be hardware or software addresses. • See Lesson 17 (Multicast IP and the MBONE) for further information. Lesson 6 - (17 of 37) Weaknesses in IP Addresses: • If a host moves to a different network, it must change it’s IP address. • If the number of hosts grows more than 255 (Class C): – The addressing scheme must be changed to a Class B. – Extremely time consuming administration changes must also be made to enable the address change. Lesson 6 - (18 of 37) Weaknesses in IP Addresses: • Routing: – Multiple IP addresses for a single host may be routed entirely different from each other. – The route chosen depends upon the address chosen (in some cases). – Knowing only one IP address for a single host may sometimes NOT be enough. Lesson 6 - (19 of 37) Weaknesses in IP Addresses: • Availability: – The number of available IP addresses is rapidly reducing, forcing temporary extensions of the IP addressing scheme, until a more scaleable scheme can be put in place. – If a stable replacement for the current IP addressing scheme is not in place within 5-10 years, all IP addresses will be completely exhausted. (IPv6) Lesson 6 - (20 of 37) Common Representation of Addresses: • Dotted Decimal Notation - a common way of representing an IP address by using four decimal integers separated by decimal points to ease in reading. • Each integer represents the value of the binary numbers contained within that octet of the address. • Example: 10000000 00001010 00000010 00011110 = 128.10.2.30 Lesson 6 - (21 of 37) Loopback Addresses: • Class A address 127.0.0.0 – Reserved for loopback on any local machine to test the communication system and for interprocess communication (IPC) on that machine. – Network 127 addresses should never appear on any network, be routed or propagated beyond the network interface card (NIC). – Commonly used as local IP addresses when configuring PCs for pseudo-SLIP connectivity. Lesson 6 - (22 of 37) Summary of Addresses: all 0s all 0s This host host all 1s net 127 Host on this net Limited broadcast (local net) all 1s anything (often 1) Directed broadcast for net Loopback Lesson 6 - (23 of 37) Obtaining an IP Address: • Network Information Center (NIC) is the central authority which ensures that all Internet addresses are unique. It does so by managing the approval and assignment of all IP network addresses. • When requesting an IP address, you should choose a type which fits the current and anticipated future sizes of your company. Lesson 6 - (24 of 37) Obtaining an IP Address: • Sample size networks and appropriate address classes: – Local Area Networks: Class C – Campus-wide Networks: Class B – Large Companies: Class B – International Networks: Class A Lesson 6 - (25 of 37) Image source: Internetworking with TCP/IP vol I (1995 Prentice Hall, Douglas Comer) Lesson 6 - (26 of 37) Obtaining an IP Address: • Applying for IP addresses is only needed if your network is going to be connected to the Internet on a permanent basis. • Currently there is a long waiting list for companies and organizations to obtain IP addresses. • The NIC may soon charge for IP addresses because of the increased demand and lack of available addresses. Lesson 6 - (27 of 37) Obtaining an IP Address: • When should an organization apply for an IP address? – Any organization that connects to the Internet has no option, they must obtain a registered number. – If an organization communicates with it’s subsidiaries using the Internet, it too must request a registered number. Lesson 6 - (28 of 37) Obtaining an IP Address: • Advantages and Disadvantages of Registering: – Advantage: • Ensuring that your address and naming conventions are protected (njit.edu). – Disadvantage: • When you connect to the Internet, your use of a registered address is recorded in the Assigned Numbers RFC along with a contact names of administrators and policy personnel.. Lesson 6 - (29 of 37) Obtaining an IP Address: • Choosing a network number without official registration: – Avoid Class A addresses. – Do not copy examples given in a configuration handbook or textbook. – Avoid well-known addresses that are published. – Use high-end Class B or C addresses at random. Lesson 6 - (30 of 37) Contacting the Network Information Center: • Contacting the NIC: – Snail Mail: Government Systems Inc, Attn: Network Information Center 14200 Park Meadow Drive Suite 200 Chantilly, VA 22021 Lesson 6 - (31 of 37) Contacting the Network Information Center (continued): – Voice: • 1-703-802-4535 • 1-800-365-DNIC – Fax: • 1-703-802-8376 – E-Mail: • NIC@NIC.DDN.MIL Lesson 6 - (32 of 37) Network Byte Ordering: • Little Endian - lowest memory address contains low-order byte of integer. • Big Endian - lowest memory address holds the high-order byte of the integer. • Direct copying may change the value of data from machine to machine. • TCP/IP protocols define Network Standard Byte Order - most signification byte first (Big Endian) Lesson 6 - (33 of 37) Mapping Names to IP Addresses: • Most users do not directly use IP addresses when using network services, they use Domain Names which map to IP addresses. • When connecting to a server at NJIT, you use the domain name (hertz.njit.edu) and not it’s IP address (128.235.251.11). • Domain names are not IP addresses, but mapped to them for readability by the Domain Naming System (Lesson 13). Lesson 6 - (34 of 37) ETHERNET 128.10.0.0 128.10.2.3 128.10.2.8 MERLIN GUENEVERE (multi-homed (Ethernet host) host) 192.5.48.3 GLATISANT (router) 192.4.48.7 128.10.2.70 TOKEN RING 192.5.48.0 128.10.2.26 LANCELOT (Ethernet host) TALIESYN (router) 192.5.48.6 10.0.0.37 192.5.48.1 ARTHUR (token ring host) To ARPANET Image source: Internetworking with TCP/IP vol I (1995 Prentice Hall, Douglas Comer) Lesson 6 - (35 of 37) Questions Addressing in TCP/IP • What range of addresses should never appear on a network? • If billions of different IP addresses can be created from 32-bits, why is there a shortage? • If we can identify computers using hardware addresses, why use IP addresses? • What are the differences between the IP addressing scheme and the U.S. telephone numbering scheme? Lesson 6 - (36 of 37) • Why have a network standard byte order? Reference Materials Addressing in TCP/IP • IP Address to Latitude/Longitude (http://cello.cs.uiuc.edu/cgi-bin/slamm/ip2ll/) • Network Information Center (NIC) (http://ds.internic.net/) • DNS Resources Directory (http://www.dns.net/dnsrd/) • Internetworking w/ TCP/IP Vol I, Douglas Comer. • Internet Standards - RFCs (ftp://nic.merit.edu/documents/std/) Lesson 6 - (37 of 37)