lesson 6 - (1 of 37) addressing in tcp/ip lesson 6 (september 22, 1995) daniel z. tabor jr. new...

Lesson 6 - (1 of 37)

Addressing in TCP/IPAddressing in TCP/IP

LESSON 6(September 22, 1995)

Daniel Z. Tabor Jr.

New Jersey Institute of Technology


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


A Need for Identification:

• There is a need to establish:– A globally accepted method of identifying

computers.– To provide a universal communication service.



• 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.



– Each address is a conceptual pair of (netid, hostid)• netid: identifies a network• hostid: identifies a host on that

network.


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.



• 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.



• 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



• 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

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• 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.

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0 1

1

4 2 3 8 24 16 31

0

1

1

1

1 1

1 1 1 1

0

0

0

0

netid

netid

netid

hostid

hostid

hostid

multicast address

reserved for future use

Class A

Class B

Class C

Class D

Class E

IPv4 Address Types:

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Network and Host IDRanges:

Address Network Range Host Range

Class A 0.0.0.0 - 127.0.0.0 0.0.0 - 255.255.255Class B 128.0.0.0 - 191.255.0.0 0.0 - 255.255Class C 192.0.0.0 - 223.255.255.0 0 - 255Class D 224.0.0.0 - 239.255.255.255 N/A

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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).

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Network and BroadcastAddresses:

• 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.

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Network and BroadcastAddresses:

• 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.

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Network and BroadcastAddresses: Notations

• 1’s => ‘All’• 0’s => ‘This’• Netid = 0 => ‘This network’

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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 MBONEMulticast IP and the MBONE) for further information.

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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.

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• 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.

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• 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)

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Common Representationof 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

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Loopback Addresses:

• Class A address 127.0.0.0– Reserved for loopback on any local machine to

test the communication system and for inter-process 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.

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all 0s

all 0s

all 1s

all 1s

host

net

127 anything (often 1)

This host

Host on this net

Limited broadcast(local net)

Directed broadcastfor net

Loopback

Summary of Addresses:

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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.

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• 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

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Image source: Internetworking with TCP/IP vol I (1995 Prentice Hall, Douglas Comer)

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• 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.

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• 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.

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• 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..

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• 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.

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Contacting the NetworkInformation Center:

• Contacting the NIC:– Snail Mail:

Government Systems Inc,

Attn: Network Information Center

14200 Park Meadow Drive

Suite 200

Chantilly, VA 22021

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Contacting the NetworkInformation Center (continued):

– Voice:• 1-703-802-4535• 1-800-365-DNIC

– Fax:• 1-703-802-8376

– E-Mail:• [email protected]

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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)

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Mapping Names toIP 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 Domain Naming System System (Lesson 13).

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ETHERNET 128.10.0.0

MERLIN(multi-homed

host)

GUENEVERE(Ethernet

host)

LANCELOT(Ethernet

host)

128.10.2.3 128.10.2.8 128.10.2.26

192.5.48.3

128.10.2.70

192.4.48.7 192.5.48.6 10.0.0.37TOKEN

RING192.5.48.0

ARTHUR (token ring host)

GLATISANT(router)

TALIESYN(router)

192.5.48.1

To ARPANET

Image source: Internetworking with

TCP/IP vol I (1995 Prentice Hall,

Douglas Comer)

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QuestionsAddressing 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?

• Why have a network standard byte order?

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Reference MaterialsAddressing 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 - (1 of 37) addressing in tcp/ip lesson 6 (september 22, 1995) daniel z. tabor jr. new...

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